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1.
Adrien W. Schmid Diego Chiappe V��r��ne Pignat Valerie Grimminger Ivan Hang Marc Moniatte Hilal A. Lashuel 《The Journal of biological chemistry》2009,284(19):13128-13142
Tissue transglutaminase (tTG) has been implicated in the pathogenesis of
Parkinson disease (PD). However, exactly how tTG modulates the structural and
functional properties of α-synuclein (α-syn) and contributes to
the pathogenesis of PD remains unknown. Using site-directed mutagenesis
combined with detailed biophysical and mass spectrometry analyses, we sought
to identify the exact residues involved in tTG-catalyzed cross-linking of
wild-type α-syn and α-syn mutants associated with PD. To better
understand the structural consequences of each cross-linking reaction, we
determined the effect of tTG-catalyzed cross-linking on the oligomerization,
fibrillization, and membrane binding of α-syn in vitro. Our
findings show that tTG-catalyzed cross-linking of monomeric α-syn
involves multiple cross-links (specifically 2-3). We subjected tTG-catalyzed
cross-linked monomeric α-syn composed of either wild-type or Gln →
Asn mutants to sequential proteolysis by multiple enzymes and peptide mapping
by mass spectrometry. Using this approach, we identified the glutamine and
lysine residues involved in tTG-catalyzed intramolecular cross-linking of
α-syn. These studies demonstrate for the first time that
Gln79 and Gln109 serve as the primary tTG reactive
sites. Mutating both residues to asparagine abolishes tTG-catalyzed
cross-linking of α-syn and tTG-induced inhibition of α-syn
fibrillization in vitro. To further elucidate the sequence and
structural basis underlying these effects, we identified the lysine residues
that form isopeptide bonds with Gln79 and Gln109. This
study provides mechanistic insight into the sequence and structural basis of
the inhibitory effects of tTG on α-syn fibrillogenesis in vivo,
and it sheds light on the potential role of tTG cross-linking on modulating
the physiological and pathogenic properties of α-syn.Parkinson disease
(PD)2 is a progressive
movement disorder that is caused by the loss of dopaminergic neurons in the
substantia nigra, the part of the brain responsible for controlling movement.
Clinically, PD is manifested in symptoms that include tremors, rigidity, and
difficulty in initiating movement (bradykinesia). Pathologically, PD is
characterized by the presence of intraneuronal, cytoplasmic inclusions known
as Lewy bodies (LB), which are composed primarily of the protein
“α-synuclein” (α-syn)
(1) and are seen in the
post-mortem brains of PD patients with the sporadic or familial forms of the
disease (2). α-Syn is a
presynaptic protein of 140 residues with a “natively” unfolded
structure (3). Three missense
point mutations in α-syn (A30P, E46K, and A53T) are associated with the
early-onset, dominant, inherited form of PD
(4,
5). Moreover, duplication or
triplication of the α-syn gene has been linked to the familial
form of PD, suggesting that an increase in α-syn expression is
sufficient to cause PD. Together, these findings suggest that α-syn
plays a central role in the pathogenesis of PD.The molecular and cellular determinants that govern α-syn
oligomerization and fibrillogenesis in vivo remain poorly understood.
In vitro aggregation studies have shown that the mutations associated
with PD (A30P, E46K, and A53T) accelerate α-syn oligomerization, but
only E46K and A53T α-syn show higher propensity to fibrillize than
wild-type (WT) α-syn
(6-8).
This suggests that oligomerization, rather than fibrillization, is linked to
early-onset familial PD (9).
Our understanding of the molecular composition and biochemical state of
α-syn in LBs has provided important clues about protein-protein
interactions and post-translational modifications that may play a role in
modulating oligomerization, fibrillogenesis, and LB formation of the protein.
In addition to ubiquitination
(10), phosphorylation
(11,
12), nitration
(13,
14), and C-terminal truncation
(15,
16), analysis of post-mortem
brain tissues from PD and Lewy bodies in dementia patients has confirmed the
colocalization of tissue transglutaminase (tTG)-catalyzed cross-linked
α-syn monomers and higher molecular aggregates in LBs within
dopaminergic neurons (17,
18). Tissue transglutaminase
catalyzes a calcium-dependent transamidating reaction involving glutamine and
lysine residues, which results in the formation of a covalent cross-link via
ε-(γ-glutamyl) lysine bonds
(Fig. 2F). To date,
seven different isoforms of tTGs have been reported, of which only tTG2 seems
to be expressed in the human brain
(19), whereas tTG1 and tTG3
are more abundantly found in stratified squamous epithelia
(20). Subsequent
immuno-histochemical, colocalization, and immunoprecipitation studies have
shown that the levels of tTG and cross-linked α-syn species are
increased in the substantia nigra of PD brains
(17). These findings, combined
with the known role of tTG in cross-linking and stabilizing bimolecular
assemblies, led to the hypothesis that tTG plays an important role in the
initiation and propagation of α-syn fibril formation and that it
contributes to fibril stability in LBs. This hypothesis was initially
supported by in vitro studies demonstrating that tTG catalyzes the
polymerization of the α-syn-derived non-amyloid component (NAC) peptide
via intermolecular covalent cross-linking of residues Gln79 and
Lys80 (21) and by
other studies suggesting that tTG promotes the fibrillization of amyloidogenic
proteins implicated in the pathogenesis of other neurodegenerative diseases
such as Alzheimer disease, supranuclear palsy, Huntington disease, and other
polyglutamine diseases
(22-24).
However, recent in vitro studies with full-length α-syn have
shown that tTG catalyzes intramolecular cross-linking of monomeric α-syn
and inhibits, rather than promotes, its fibrillization in vitro
(25,
26). The structural basis of
this inhibitory effect and the exact residues involved in tTG-mediated
cross-linking of α-syn, as well as structural and functional
consequences of these modifications, remain poorly understood.Open in a separate windowFIGURE 2.tTG-catalyzed cross-linking of α-syn involves one to three
intramolecular cross-links. A-C, MALDI-TOF/TOF analysis of native
(—) and cross-linked (- - -) α-syn, showing that most
tTG-catalyzed cross-linking products of WT or disease-associated mutant forms
of α-syn are intramolecularly linked (predominant peak with two
cross-links), and up to three intramolecular cross-links can occur (left
shoulder). The abbreviations M and m/cl are
used to designate native and cross-linked α-synuclein, respectively.
D and E, kinetic analysis of α-syn (A30P)
cross-linking monitored by MALDI-TOF and SDS-PAGE. F, schematic
depiction of the tTG-catalyzed chemical reaction (isodipeptide formation)
between glutamine and lysine residues.In this study, we have identified the primary glutamine and lysine residues
involved in tTG-catalyzed, intramolecularly cross-linked monomeric α-syn
and investigated how cross-linking these residues affects the oligomerization,
fibrillization, and membrane binding of α-syn in vitro. Using
single-site mutagenesis and mass spectrometry applied to exhaustive
proteolytic digests of native and cross-linked monomeric α-syn, we
identified Gln109 and Gln79 as the major tTG substrates.
We demonstrate that the altered electrophoretic mobility of the
intramolecularly cross-linked α-syn in SDS-PAGE occurs as a result of
tTG-catalyzed cross-linking of Gln109 to lysine residues in the N
terminus of α-syn, which leads to the formation of more compact
monomers. Consistent with previous studies, we show that intramolecularly
cross-linked α-syn forms off-pathway oligomers that are distinct from
those formed by the wild-type protein and that do not convert to fibrils
within the time scale of our experiments (3-5 days). We also show that
membrane-bound α-syn is a substrate of tTG and that intramolecular
cross-linking does not interfere with the ability of monomeric α-syn to
adopt an α-helical conformation upon binding to synthetic membranes.
These studies provide novel mechanistic insight into the sequence and
structural basis of events that allow tTG to inhibit α-syn
fibrillogenesis, and they shed light on the potential role of tTG-catalyzed
cross-linking in modulating the physiological and pathogenic properties of
α-syn. 相似文献
2.
3.
Intracellular β-Carbonic Anhydrase of the Unicellular Green
Alga Coccomyxa
: Cloning of the cDNA and Characterization of the Functional
Enzyme Overexpressed in Escherichia coli
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Thomas Hiltonen Harry Bj?rkbacka Cecilia Forsman Adrian K. Clarke G?ran Samuelsson 《Plant physiology》1998,117(4):1341-1349
Carbonic anhydrase (CA) (EC 4.2.1.1) enzymes catalyze the reversible hydration of CO2, a reaction that is important in many physiological processes. We have cloned and sequenced a full-length cDNA encoding an intracellular β-CA from the unicellular green alga Coccomyxa. Nucleotide sequence data show that the isolated cDNA contains an open reading frame encoding a polypeptide of 227 amino acids. The predicted polypeptide is similar to β-type CAs from Escherichia coli and higher plants, with an identity of 26% to 30%. The Coccomyxa cDNA was overexpressed in E. coli, and the enzyme was purified and biochemically characterized. The mature protein is a homotetramer with an estimated molecular mass of 100 kD. The CO2-hydration activity of the Coccomyxa enzyme is comparable with that of the pea homolog. However, the activity of Coccomyxa CA is largely insensitive to oxidative conditions, in contrast to similar enzymes from most higher plants. Fractionation studies further showed that Coccomyxa CA is extrachloroplastic. 相似文献
4.
Six species of Gastrocopta have been identified from the Pilbara region, Western Australia, by means of comparative analyses of shell and mtDNA variation. Three of these species, Gastrocopta hedleyi, Gastrocopta larapinta and Gastrocopta servilis, have been recorded in the Pilbara for the first time. Gastrocopta sp. CW1 is probably new to science and might be endemic to the region. By contrast, Gastrocopta hedleyi, Gastrocopta larapinta and Gastrocopta mussoni are shown to be widespread. 相似文献
5.
The tiger beetle fauna of the Balkan Peninsula is one of the richest in Europe and includes 19 species or 41% of the European tiger beetle fauna. Assembled by their biogeographical origins, the Balkan tiger beetle species fall into 14 different groups that include, Mediterranean, Middle Oriental, Central Asiatic, Euro-Siberian, South and East European, Pannonian-Sarmatian, West Palaearctic, Turano-European and Afrotropico Indo-Mediterranean species. The Mediterranean Sclerophyl and the Pontian Steppe are the Balkan biogeographical provinces with the highest species richness, while the Balkan Highlands has the lowest Cicindelidae diversity. Most species are restricted to single habitat types in lowland areas of the Balkan Peninsula and only Calomera aulica aulica and Calomera littoralis nemoralis occur in respectively 3 and 4 different types of habitat. About 60% of all Balkan Cicindelidae species are found in habitats potentially endangered by human activity. 相似文献
6.
7.
Nelli Mnatsakanyan Arathianand M. Krishnakumar Toshiharu Suzuki Joachim Weber 《The Journal of biological chemistry》2009,284(17):11336-11345
ATP synthase uses a unique rotational mechanism to convert chemical energy
into mechanical energy and back into chemical energy. The helix-turn-helix
motif, termed “DELSEED-loop,” in the C-terminal domain of the
β subunit was suggested to be involved in coupling between catalysis and
rotation. Here, the role of the DELSEED-loop was investigated by functional
analysis of mutants of Bacillus PS3 ATP synthase that had 3–7
amino acids within the loop deleted. All mutants were able to catalyze ATP
hydrolysis, some at rates several times higher than the wild-type enzyme. In
most cases ATP hydrolysis in membrane vesicles generated a transmembrane
proton gradient, indicating that hydrolysis occurred via the normal rotational
mechanism. Except for two mutants that showed low activity and low abundance
in the membrane preparations, the deletion mutants were able to catalyze ATP
synthesis. In general, the mutants seemed less well coupled than the wild-type
enzyme, to a varying degree. Arrhenius analysis demonstrated that in the
mutants fewer bonds had to be rearranged during the rate-limiting catalytic
step; the extent of this effect was dependent on the size of the deletion. The
results support the idea of a significant involvement of the DELSEED-loop in
mechanochemical coupling in ATP synthase. In addition, for two deletion
mutants it was possible to prepare an
α3β3γ subcomplex and measure nucleotide
binding to the catalytic sites. Interestingly, both mutants showed a severely
reduced affinity for MgATP at the high affinity site.F1F0-ATP synthase catalyzes the final step of
oxidative phosphorylation and photophosphorylation, the synthesis of ATP from
ADP and inorganic phosphate. F1F0-ATP synthase consists
of the membrane-embedded F0 subcomplex, with, in most bacteria, a
subunit composition of ab2c10, and the peripheral
F1 subcomplex, with a subunit composition of
α3β3γδε. The energy
necessary for ATP synthesis is derived from an electrochemical transmembrane
proton (or, in some organisms, a sodium ion) gradient. Proton flow down the
gradient through F0 is coupled to ATP synthesis on F1 by
a unique rotary mechanism. The protons flow through (half) channels at the
interface of the a and c subunits, which drives rotation of the ring of c
subunits. The c10 ring, together with F1 subunits
γ and ε, forms the rotor. Rotation of γ leads to
conformational changes in the catalytic nucleotide binding sites on the β
subunits, where ADP and Pi are bound. The conformational changes
result in the formation and release of ATP. Thus, ATP synthase converts
electrochemical energy, the proton gradient, into mechanical energy in the
form of subunit rotation and back into chemical energy as ATP. In bacteria,
under certain physiological conditions, the process runs in reverse. ATP is
hydrolyzed to generate a transmembrane proton gradient, which the bacterium
requires for such functions as nutrient import and locomotion (for reviews,
see Refs.
1–6).F1 (or F1-ATPase) has three catalytic nucleotide
binding sites located on the β subunits at the interface to the adjacent
α subunit. The catalytic sites have pronounced differences in their
nucleotide binding affinity. During rotational catalysis, the sites switch
their affinities in a synchronized manner; the position of γ determines
which catalytic site is the high affinity site
(Kd1 in the nanomolar range), which site is the
medium affinity site (Kd2 ≈ 1
μm), and which site is the low affinity site
(Kd3 ≈ 30–100 μm; see
Refs. 7 and
8). In the original crystal
structure of bovine mitochondrial F1
(9), one of the three catalytic
sites, was filled with the ATP analog
AMP-PNP,2 a second was
filled with ADP (plus azide) (see Ref.
10), and the third site was
empty. Hence, the β subunits are referred to as βTP,
βDP, and βE. The occupied β subunits,
βTP and βDP, were in a closed conformation,
and the empty βE subunit was in an open conformation. The main
difference between these two conformations is found in the C-terminal domain.
Here, the “DELSEED-loop,” a helix-turn-helix structure containing
the conserved DELSEED motif, is in an “up” position when the
catalytic site on the respective β subunit is filled with nucleotide and
in a “down” position when the site is empty
(Fig. 1A). When all
three catalytic sites are occupied by nucleotide, the previously open
βE subunit assumes an intermediate, half-closed
(βHC) conformation. It cannot close completely because of
steric clashes with γ
(11).Open in a separate windowFIGURE 1.The βDELSEED-loop. A, interaction of the
βTP and βE subunits with theγ
subunit.β subunits are shown in yellow andγ in
blue. The DELSEED-loop (shown in orange, with the DELSEED
motif itself in green)of βTP interacts with the
C-terminal helixγ and the short helix that runs nearly perpendicular to
the rotation axis. The DELSEED-loop of βE makes contact with
the convex portion of γ, formed mainly by the N-terminal helix. A
nucleotide molecule (shown in stick representation) occupies the catalytic
site of βTP, and the subunit is in the closed conformation.
The catalytic site on βE is empty, and the subunit is in the
open conformation. This figure is based on Protein Data Bank file 1e79
(32). B, deletions in
the βDELSEED-loop. The loop was “mutated” in silico
to represent the PS3 ATP synthase. The 3–4-residue segments that are
removed in the deletion mutants are color-coded as follows:
380LQDI383, pink;
384IAIL387, green;
388GMDE391, yellow;
392LSD394, cyan;
395EDKL398, orange;
399VVHR402, blue. Residues that are the most
involved in contacts with γ are labeled. All figures were generated
using the program PyMOL (DeLano Scientific, San Carlos, CA).The DELSEED-loop of each of the three β subunits makes contact with
the γ subunit. In some cases, these contacts consist of hydrogen bonds
or salt bridges between the negatively charged residues of the DELSEED motif
and positively charged residues on γ. The interactions of the
DELSEED-loop with γ, its movement during catalysis, the conservation of
the DELSEED motif (see 12–14).
Thus, the finding that an AALSAAA mutant in the
α3β3γ complex of ATP synthase from the
thermophilic Bacillus PS3, where several hydrogen bonds/salt bridges
to γ are removed simultaneously, could drive rotation of γ with
the same torque as the wild-type enzyme
(14) came as a surprise. On
the other hand, it seems possible that it is the bulk of the DELSEED-loop,
more so than individual interactions, that drives rotation of γ.
According to a model favored by several authors
(6,
15,
16) (see also Refs.
17–19),
binding of ATP (or, more precisely, MgATP) to the low affinity catalytic site
on βE and the subsequent closure of this site, accompanied by
its conversion into the high affinity site, are responsible for driving the
large (80–90°) rotation substep during ATP hydrolysis, with the
DELSEED-loop acting as a “pushrod.” A recent molecular dynamics
(20) study supports this model
and implicates mainly the region around several hydrophobic residues upstream
of the DELSEED motif (specifically βI386 and
βL387)3 as being
responsible for making contact with γ during the large rotation
substep.
TABLE 1
Conservation of residues in the DELSEED-loop Amino acids found in selected species in the turn region of the DELSEED-loop. Listed are all positions subjected to deletions in the present study. Residue numbers refer to the PS3 enzyme. Consensus annotation: p, polar residue; s, small residue; h, hydrophobic residue; –, negatively charged residue; +, positively charged residue.Open in a separate windowIn the present study, we investigated the function of the DELSEED-loop using an approach less focused on individual residues, by deleting stretches of 3–7 amino acids between positions β380 and β402 of ATP synthase from the thermophilic Bacillus PS3. We analyzed the functional properties of the deletion mutants after expression in Escherichia coli. The mutants showed ATPase activities, which were in some cases surprisingly high, severalfold higher than the activity of the wild-type control. On the other hand, in all cases where ATP synthesis could be measured, the rates where below or equal to those of the wild-type enzyme. In Arrhenius plots, the hydrolysis rates of the mutants were less temperature-dependent than those of wild-type ATP synthase. In those cases where nucleotide binding to the catalytic sites could be tested, the deletion mutants had a much reduced affinity for MgATP at high affinity site 1. The functional role of the DELSEED-loop will be discussed in light of the new information. 相似文献8.
9.
The three key players in the exocytotic release of neurotransmitters from
synaptic vesicles are the SNARE (soluble N-ethylmaleimide-sensitive
factor attachment protein receptor) proteins synaptobrevin 2, syntaxin 1a, and
SNAP-25. Their assembly into a tight four-helix bundle complex is thought to
pull the two membranes into close proximity. It is debated, however, whether
the energy generated suffices for membrane fusion. Here, we have determined
the thermodynamic properties of the individual SNARE assembly steps by
isothermal titration calorimetry. We found extremely large favorable enthalpy
changes counterbalanced by positive entropy changes, reflecting the major
conformational changes upon assembly. To circumvent the fact that ternary
complex formation is essentially irreversible, we used a stabilized
syntaxin-SNAP-25 heterodimer to study synaptobrevin binding. This strategy
revealed that the N-terminal synaptobrevin coil binds reversibly with
nanomolar affinity. This suggests that individual, membrane-bridging SNARE
complexes can provide much less pulling force than previously claimed.The molecular machinery that drives the Ca2+-dependent release
of neurotransmitters from synaptic vesicles is studied intensively. Three key
players in the underlying exocytotic fusion of the vesicle with the plasma
membrane are the proteins synaptobrevin 2/VAMP2 (vesicle-associated membrane
protein), syntaxin 1a, and
SNAP-253 (for review,
see Refs.
1-7).
They belong to the so-called SNARE protein family, the members of which are
involved in all vesicle fusion steps in the endocytic and secretory pathway.
In general, SNARE proteins are relatively small, tail-anchored membrane
proteins. Their key characteristic is the so-called SNARE motif, an extended
stretch of heptad repeats that is usually connected to a single transmembrane
domain by a short linker. Syntaxin and synaptobrevin each contain a single
SNARE motif, whereas SNAP-25 contains two SNARE motifs connected by a
palmitoylated linker region serving as a membrane anchor. The SNARE motifs of
the three proteins assemble into a very tight four-helix bundle between
opposing membranes; during this process the plasma membrane proteins syntaxin
and SNAP-25 provide the binding site for the vesicular synaptobrevin.
Formation of this complex is accompanied by extensive structural
rearrangements
(8-10).
Based on these findings, it was put forward that the formation of the SNARE
bundle provides the energy that drives membrane fusion. As the bundle is
oriented in parallel, it is thought that formation of this complex starts from
the membrane-proximal N termini and proceeds toward the C-terminal membrane
anchors, effectively pulling the membranes together (the “zipper”
model) (11). Although the
zipper scenario is intuitive, it has been difficult to demonstrate
directly.A decade ago it was shown that the three neuronal SNARE proteins are
sufficient to fuse artificial vesicles
(12). However, this
reductionist approach yields rather slow fusion rates
(12-14).
Over the years various different end products of SNARE catalysis (complete
fusion, hemifusion, and only tethered membranes) have been reported
(15-19).
These unsatisfactory results have fueled the debate over whether the assembly
process indeed provides enough impetus to fuse bilayers. Not surprisingly, an
alternative scenario has been put forward in which repulsive forces between
membranes bring the SNARE assembly to a grinding halt. According to this idea,
other factors like the Ca2+ sensor synaptotagmin or the small
soluble protein complexin are needed to induce membrane merging
(20-22).In simple terms, to find out whether the SNARE complex assembly is enough
for membrane fusion, only the amount of energy released during complex
formation and the amount of energy needed for membrane fusion need to be
compared. However, the physics of membrane fusion are very complicated, and it
is even more challenging to understand how proteins modulate the process. The
free energy for bilayer fusion in an aqueous environment is not very high, but
fusion is thought to require a large activation energy of about 40
kBT, as two charged membranes have to be brought into close
apposition. According to a theoretical model, the apposing membranes then need
to be modified into a stalk-like configuration. Before fusion occurs, the
process is thought to pass through a hemifusion intermediate in which only the
outer monolayers are merged (for review, see Refs.
23 and
24). The role of fusion
proteins is thought to lower the energy barrier for membrane fusion, but
understanding how they modulate the lipid membrane and how their
conformational changes are translated into a mechanical force is still in its
infancy. It is not clear, for instance, whether SNARE-catalyzed fusion indeed
proceeds through a stalk-like structure or just locally alters the membranes,
a mechanism that might need much less activation energy.As the folding and unfolding transitions of the ternary SNARE complex
exhibit a marked hysteresis
(25), the question of how much
energy is released during complex formation has been difficult to answer as
well. To avoid the quasi-irreversibility of the process, the problem has been
elegantly tackled by atomic force microscopy by two different research groups
(26-28).
In these experiments individual complexes affixed to solid supports were
ruptured, yielding energy values of 43 and 33 kBT. In another
approach, which used a surface-force apparatus (SFA), a comparable energy of
35 kBT has recently been determined
(29). Strikingly, these values
appear to correspond closely with the activation energy needed to fuse two
membranes, substantiating the view that SNAREs are nano-fusion machineries.
However, one should be cautious about the conclusion that these sophisticated
procedures in fact yield the genuine SNARE assembly energy. For example, with
the SFA approach, the number of complexes had to be deduced rather indirectly
to estimate the free energy. Moreover, these approaches offered only indirect
information about the reaction pathway.In this study we set out to determine the SNARE assembly energy more
directly by using isothermal titration calorimetry (ITC) complemented by
kinetic measurements. ITC is a powerful technique for studying the
thermodynamics of macromolecular interactions by directly measuring the heat
changes associated with complex formation, which at constant pressure is equal
to the enthalpy change (ΔH). The titration approach also yields
the stoichiometry (n), the entropy change (ΔS), and
the association constant (KA) of the reaction. We studied
the consecutive reaction steps individually to gain deeper insights into the
rugged energy landscape of complex formation. To study synaptobrevin binding
in isolation, we used a stabilized syntaxin-SNAP-25 heterodimer, which has
been shown to greatly accelerate liposome fusion rates
(30). This strategy revealed
that the N-terminal coil of synaptobrevin binds reversibly, making it feasible
to access the free energy of SNARE assembly. Overall, our results suggest that
individual SNARE complexes might provide much less pulling energy than
previously claimed. 相似文献
10.
Vítor Yamashiro Rocha Soares Jailthon Carlos da Silva Kleverton Ribeiro da Silva Maria do Socorro Pires e Cruz Marcos Pérsio Dantas Santos Paulo Eduardo Martins Ribolla Diego Peres Alonso Luiz Felipe Leomil Coelho Dorcas Lamounier Costa Carlos Henrique Nery Costa 《Memórias do Instituto Oswaldo Cruz》2014,109(3):379-383
An analysis of the dietary content of haematophagous insects can provide important
information about the transmission networks of certain zoonoses. The present study
evaluated the potential of polymerase chain reaction-restriction fragment length
polymorphism (PCR-RFLP) analysis of the mitochondrial cytochrome B (cytb)
gene to differentiate between vertebrate species that were identified as
possible sources of sandfly meals. The complete cytb gene sequences
of 11 vertebrate species available in the National Center for Biotechnology
Information database were digested with Aci I, Alu
I, Hae III and Rsa I restriction
enzymes in silico using Restriction Mapper software. The
cytb gene fragment (358 bp) was amplified from tissue samples of
vertebrate species and the dietary contents of sandflies and digested with
restriction enzymes. Vertebrate species presented a restriction fragment profile that
differed from that of other species, with the exception of Canis familiaris
and Cerdocyon thous. The 358 bp fragment was identified
in 76 sandflies. Of these, 10 were evaluated using the restriction enzymes and the
food sources were predicted for four: Homo sapiens (1), Bos
taurus (1) and Equus caballus (2). Thus, the PCR-RFLP
technique could be a potential method for identifying the food sources of arthropods.
However, some points must be clarified regarding the applicability of the method,
such as the extent of DNA degradation through intestinal digestion, the potential for
multiple sources of blood meals and the need for greater knowledge regarding
intraspecific variations in mtDNA. 相似文献
11.
The DSM-IV major depression "bereavement exclusion" (BE), which recognizes that depressive symptoms are sometimes normal in recently bereaved individuals, is proposed for elimination in DSM-5. Evidence cited for the BE's invalidity comes from two 2007 reviews purporting to show that bereavement-related depression is similar to other depression across various validators, and a 2010 review of subsequent research. We examined whether the 2007 and 2010 reviews and subsequent relevant literature support the BE's invalidity. Findings were: a) studies included in the 2007 reviews sampled bereavement-related depression groups most of whom were not BE-excluded, making them irrelevant for evaluating BE validity; b) three subsequent studies cited by the 2010 review as supporting BE elimination did examine BE-excluded cases but were in fact inconclusive; and c) two more recent articles comparing recurrence of BE-excluded and other major depressive disorder cases both support the BE's validity. We conclude that the claimed evidence for the BE's invalidity does not exist. The evidence in fact supports the BE's validity and its retention in DSM-5 to prevent false positive diagnoses. We suggest some improvements to increase validity and mitigate risk of false negatives. 相似文献
12.
Ajit K. Satapathy Donald J. Crampton Benjamin B. Beauchamp Charles C. Richardson 《The Journal of biological chemistry》2009,284(21):14286-14295
The multifunctional protein encoded by gene 4 of bacteriophage T7 (gp4)
provides both helicase and primase activity at the replication fork. T7 DNA
helicase preferentially utilizes dTTP to unwind duplex DNA in vitro
but also hydrolyzes other nucleotides, some of which do not support helicase
activity. Very little is known regarding the architecture of the nucleotide
binding site in determining nucleotide specificity. Crystal structures of the
T7 helicase domain with bound dATP or dTTP identified Arg-363 and Arg-504 as
potential determinants of the specificity for dATP and dTTP. Arg-363 is in
close proximity to the sugar of the bound dATP, whereas Arg-504 makes a
hydrogen bridge with the base of bound dTTP. T7 helicase has a serine at
position 319, whereas bacterial helicases that use rATP have a threonine in
the comparable position. Therefore, in the present study we have examined the
role of these residues (Arg-363, Arg-504, and Ser-319) in determining
nucleotide specificity. Our results show that Arg-363 is responsible for dATP,
dCTP, and dGTP hydrolysis, whereas Arg-504 and Ser-319 confer dTTP
specificity. Helicase-R504A hydrolyzes dCTP far better than wild-type
helicase, and the hydrolysis of dCTP fuels unwinding of DNA. Substitution of
threonine for serine 319 reduces the rate of hydrolysis of dTTP without
affecting the rate of dATP hydrolysis. We propose that different nucleotides
bind to the nucleotide binding site of T7 helicase by an induced fit
mechanism. We also present evidence that T7 helicase uses the energy derived
from the hydrolysis of dATP in addition to dTTP for mediating DNA
unwinding.Helicases are molecular machines that translocate unidirectionally along
single-stranded nucleic acids using the energy derived from nucleotide
hydrolysis
(1–3).
The gene 4 protein encoded by bacteriophage T7 consists of a helicase domain
and a primase domain, located in the C-terminal and N-terminal halves of the
protein, respectively (4). The
T7 helicase functions as a hexamer and has been used as a model to study
ring-shaped replicative helicases. In the presence of dTTP, T7 helicase binds
to single-stranded DNA
(ssDNA)3 as a hexamer
and translocates 5′ to 3′ along the DNA strand using the energy of
hydrolysis of dTTP
(5–7).
T7 helicase hydrolyzes a variety of ribo and deoxyribonucleotides; however,
dTTP hydrolysis is optimally coupled to DNA unwinding
(5).Most hexameric helicases use rATP to fuel translocation and unwind DNA
(3). T7 helicase does hydrolyze
rATP but with a 20-fold higher Km as compared with dTTP
(5,
8). It has been suggested that
T7 helicase actually uses rATP in vivo where the concentration of
rATP is 20-fold that of dTTP in the Escherichia coli cell
(8). However, hydrolysis of
rATP, even at optimal concentrations, is poorly coupled to translocation and
unwinding of DNA (9). Other
ribonucleotides (rCTP, rGTP, and rUTP) are either not hydrolyzed or the poor
hydrolysis observed is not coupled to DNA unwinding
(8). Furthermore, Patel et
al. (10) found that the
form of T7 helicase found in vivo, an equimolar mixture of the
full-length gp4 and a truncated form lacking the zinc binding domain of the
primase, prefers dTTP and dATP. Therefore, in the present study we have
restricted our examination of nucleotides to the deoxyribonucleotides.The nucleotide binding site of the replicative DNA helicases, such as T7
gene 4 protein, bind nucleotides at the subunit interface
(Fig. 1) located between two
RecA-like subdomains that bind ATP
(11,
12). The location of the
nucleotide binding site at the subunit interface provides multiple
interactions of residues with the bound NTP. A number of cis- and
trans-acting amino acids stabilize the bound nucleotide in the
nucleotide binding site and also provide for communication between subunits
(13–15).
Earlier reports revealed that the arginine finger (Arg-522) in T7 helicase is
positioned to interact with the γ-phosphate of the bound nucleotide in
the adjacent subunit (12,
16). However, His-465
(phosphate sensor), Glu-343 (catalytic base), and Asp-424 (Walker motif B)
interacts with the γ-phosphate of the bound nucleotide in the same
subunit (12,
17,
18). The arginine finger and
the phosphate sensor have been proposed to couple NTP hydrolysis to DNA
unwinding. Substitution of Glu-343, the catalytic base, eliminates dTTP
hydrolysis (19), and
substitution of Asp-424 with Asn leads to a severe reduction in dTTP
hydrolysis (20). The conserved
Lys-318 in Walker motif A interacts with the β-phosphate of the bound
nucleotide and plays an important role in dTTP hydrolysis
(21).Open in a separate windowFIGURE 1.Crystal structure of T7 helicase. A, crystal structure of
the hexameric helicase C-terminal domain of gp4
(17). The structure reveals a
ring-shaped molecule with a central core through which ssDNA passes. The
inset shows the interface between two subunits of the helicase with
adenosine 5′-{β,γ-imidol}-triphosphate in the nucleotide
binding site. B, the nucleotide binding site of a monomer of the gp4
with the crucial amino acid residues reported earlier and in the present study
is shown in sticks. The crystal structures of the T7 gene 4 helicase
domain (12) with bound dTTP
(C) and dATP (D). The structures shown are the nucleotide
binding site of T7 helicase as viewed in Pymol by analyzing the PDB files 1cr1
and 1cr2 (12). Arg-504 and
Tyr-535 sandwiches the base of the bound dNTP. Additionally, Arg-504 forms a
hydrogen bridge with dTTP. Arg-363 interacts specifically with the 3-OH group
of bound dATP. AMPPNP, adenosine
5′-(β,γ-imino)triphosphate.Considering the wealth of information on the above residues that are
involved in the hydrolysis of dTTP and the coupling of hydrolysis to
unwinding, it is intriguing that little information is available on nucleotide
specificity. Several crystal structures of T7 helicase in complex with a
nucleotide triphosphate are available. However, most of structures were
crystallized with a non-hydrolyzable analogue of dTTP or the nucleotide was
diffused into the crystal. The crystal structure of the T7 helicase domain
bound with dTTP or dATP was reported by Sawaya et al.
(12). These structures
assisted us in identifying two basic residues (Arg-363 and Arg-504) in close
proximity to the sugar and base of the bound nucleotide whose orientation
suggested that these residues could be involved in nucleotide selection.
Arg-504 together with Tyr-535 sandwich the base of the bound nucleotide at the
subunit interface of the hexameric helicase
(Fig. 1). Arg-504 and Tyr-535
are structurally well conserved in various helicases
(12). However, Arg-504 could
make a hydrogen bridge with the OH group of thymidine, thus suggesting a role
in dTTP specificity. On the other hand, Arg-363 is in close proximity
(∼3.4 Å) to the sugar 3′-OH of bound dATP, whereas in the
dTTP-bound structure this residue is displaced by 7.12 Å
(Fig. 1) from the equivalent
position. Consequently Arg-363 could play a role in dATP binding. The crystal
structures do not provide any information on different interaction of residues
with the phosphates of dATP and dTTP. However, alignment of the residues in
the P-loops of different hexameric helicases reveals that the serine adjacent
to the invariant lysine at position 319 (Ser-319) is conserved in
bacteriophages, whereas bacterial helicases have a conserved threonine in the
equivalent position (supplemental Fig. 1). Bacterial helicases use rATP in the
DNA unwinding reactions. whereas T7 helicase preferentially uses dTTP, and
bacteriophage T4 gene 41 uses rGTP or rATP
(22).Although considerable information is available on the role of residues in
nucleotide binding and dTTP hydrolysis, very little is known on the
determinants of nucleotide specificity. In the present study we made an
attempt to address the role of a few selected residues (Arg-363, Arg-504, and
Ser-319) in determining nucleotide specificity, especially dTTP and dATP, both
of which are hydrolyzed and mediate DNA unwinding. We show that under
physiological conditions T7 helicase uses the energy derived from the
hydrolysis of dATP in addition to dTTP for mediating DNA unwinding. 相似文献
13.
14.
15.
The European bone-skippers (Diptera: Piophilidae: Thyreophorina), long considered extinct, have recently been the object of much interest by dipterists after their unexpected rediscovery. Considerable faunistic work has been done on these flies in recent years. However, some nomenclatural and taxonomic issues still require attention. A neotype is designated for Thyreophora anthropophaga Robineau-Desvoidy, 1830 (now in the genus Centrophlebomyia Hendel, 1903) to fix the identity of this nominal species. Centrophlebomyia anthropophaga is recognized as a valid species. It is described and illustrated in detail, and information on its preimaginal instars is provided for the first time. Four Palaearctic species of Centrophlebomyia are recognized and reviewed and a key is provided for their identification. Centrophlebomyia orientalis Hendel, 1907 from northern India, is removed from synonymy with Centrophlebomyia anthropophaga and recognized as a valid species of Centrophlebomyia, stat. r. The nominal genus Protothyreophora Ozerov, 1984 is considered a junior synonym of Centrophlebomyia, syn. n. 相似文献
16.
Victoria L Alonso Carla Ritagliati Pamela Cribb Esteban C Serra 《Memórias do Instituto Oswaldo Cruz》2014,109(8):1081-1085
We present here three expression plasmids for Trypanosoma cruzi
adapted to the Gateway® recombination cloning system. Two of
these plasmids were designed to express trypanosomal proteins fused to a double tag
for tandem affinity purification (TAPtag). The TAPtag and Gateway®
cassette were introduced into an episomal (pTEX) and an integrative (pTREX) plasmid.
Both plasmids were assayed by introducing green fluorescent protein (GFP) by
recombination and the integrity of the double-tagged protein was determined by
western blotting and immunofluorescence microscopy. The third Gateway adapted vector
assayed was the inducible pTcINDEX. When tested with GFP,
pTcINDEX-GW showed a good response to tetracycline, being less
leaky than its precursor (pTcINDEX). 相似文献
17.
Nik A. B. N. Mahmood Esther Biemans-Oldehinkel Bert Poolman 《The Journal of biological chemistry》2009,284(21):14368-14376
We have previously shown that the C-terminal cystathionine β-synthase
(CBS) domains of the nucleotide-binding domains of the ABC transporter OpuA,
in conjunction with an anionic membrane surface function, act as sensor of
internal ionic strength (Iin). Here, we show that a
surface-exposed cationic region in the CBS module domain is critical for ion
sensing. The consecutive substitution of up to five cationic residues led to a
gradual decrease of the ionic strength dependence of transport. In fact, a
5-fold mutant was essentially independent of salt in the range from 0 to 250
mm KCl (or NaCl), supplemented to medium of 30 mm
potassium phosphate. Importantly, the threshold temperature for transport was
lowered by 5–7 °C and the temperature coefficient
Q10 was lowered from 8 to ∼1.5 in the 5-fold mutant,
indicating that large conformational changes are accompanying the CBS-mediated
regulation of transport. Furthermore, by replacing the anionic C-terminal tail
residues that extend the CBS module with histidines, the transport of OpuA
became pH-dependent, presumably by additional charge interactions of the
histidine residues with the membrane. The pH dependence was not observed at
high ionic strength. Altogether the analyses of the CBS mutants support the
notion that the osmotic regulation of OpuA involves a simple biophysical
switching mechanism, in which nonspecific electrostatic interactions of a
protein module with the membrane are sufficient to lock the transporter in the
inactive state.In their natural habitats microorganisms are often exposed to changes in
the concentration of solutes in the environment
(1). A sudden increase in the
medium osmolality results in loss of water from the cell, loss of turgor, a
decrease in cell volume, and an increase in intracellular osmolyte
concentration. Osmoregulatory transporters such as OpuA in Lactococcus
lactis, ProP in Escherichia coli, and BetP in
Corynebacterium glutamicum diminish the consequences of the osmotic
stress by mediating the uptake of compatible solutes upon an increase in
extracellular osmolality
(2–4).
For the ATP-binding cassette
(ABC)5 transporter
OpuA, it has been shown that the system, reconstituted in proteoliposomes, is
activated by increased concentrations of lumenal ions (increased internal
ionic strength) (2,
5,
6). This activation is
instantaneous both in vivo and in vitro and only requires
threshold levels of ionic osmolytes. Moreover, the ionic threshold for
activation is highly dependent of the ionic lipid content (charge density) of
the membrane and requires the presence of so-called cystathionine
β-synthase (CBS) domains, suggesting that the ionic signal is transduced
to the transporter via critical interactions of the protein with membrane
lipids.The ABC transporter OpuA consists of two identical nucleotide-binding
domains (NBD) fused to CBS domains and two identical substrate-binding domains
fused to transmembrane domains. The NBD-CBS and substrate-binding
domain-transmembrane domain subunits are named OpuAA and OpuABC, respectively.
Two tandem CBS domains are linked to the C-terminal end of the NBD; each
domain (CBS1 and CBS2) has a β-α-β-β-α secondary
structure (5)
(Fig. 1A). The CBS
domains are widely distributed in most if not all species of life but their
function is largely unknown. Most of the CBS domains are found as tandem
repeats but data base searches have also revealed tetra-repeat units
(5). The crystal structures of
several tandem CBS domains have been elucidated
(7–9,
32), and in a number of cases
it has been shown that two tandem CBS domains form dimeric structures with a
total of four CBS domains per structural module (hereafter referred to as CBS
module). The crystal structures of the full-length MgtE Mg2+
transporter confirm the dimeric configuration and show that the CBS domains
undergo large conformational changes upon Mg2+ binding or release
(10,
11). In general, ABC
transporters are functional as dimers, which implies that two tandem CBS
domains are present in the OpuA complex. Preliminary experiments with
disulfides engineered at the interface of two tandem CBS domains in OpuA
suggest that large structural rearrangements (association-dissociation of the
interfaces) play a determining role in the ionic strength-regulated transport.
Finally, a subset of CBS-containing proteins has a C-terminal extension, which
in OpuA is highly anionic (sequence: ADIPDEDEVEEIEKEEENK) and modulates the
ion sensing activity (6).Open in a separate windowFIGURE 1.Domain structure of CBS module of OpuA. A, sequence of
tandem CBS domains. The predicted secondary structure is indicated
above the sequence. The residues modified in this study are
underlined. The amino acid sequence end-points of OpuAΔ61 and
OpuAΔ119 are indicated by vertical arrows. B, homology
model of tandem CBS domain of OpuA. The CBS domains were individually modeled
on the crystal structure of the tandem CBS protein Ta0289 from T.
acidophilum (PDB entry 1PVM), using Phyre. Ta0289 was used for the
initial modeling, because its primary sequence was more similar to the CBS
domains of OpuA than those of the other crystallized CBS proteins. The
individual domain models were then assembled with reference to the atomic
coordinates of the tandem CBS domains of IMPDH from Streptococcus
pyogenes (PDB entry 1ZFJ) to form the tandem CBS pair, using PyMOL
(DeLano). The positions of the (substituted) cationic residues are
indicated.In this study, we have engineered the surface-exposed cationic residues of
the CBS module and the C-terminal anionic tail of OpuA
(Fig. 1B). The ionic
strength and lipid dependence of the OpuA mutants were determined in
vivo and in vitro. We show that substitution of five cationic
residues for neutral amino acids is sufficient to inactivate the ionic
strength sensor and convert OpuA into a constitutively active transporter.
Moreover, by substituting six anionic plus four neutral residues of the
C-terminal anionic tail for histidines, the transport reaction becomes
strongly pH-dependent. 相似文献
18.
Here we describe and illustrate a new parasitoid wasp species, Lathrolestes gauldi
sp. n. from the lowland rainforest of eastern Ecuador and provide a key to the Neotropical species of the genus. This is the first record of the subfamily Ctenopelmatinae from Ecuador. 相似文献
19.
Yongmei Pu Susan H. Garfield Noemi Kedei Peter M. Blumberg 《The Journal of biological chemistry》2009,284(2):1302-1312
Classic and novel protein kinase C (PKC) isozymes contain two zinc finger
motifs, designated “C1a” and “C1b” domains, which
constitute the recognition modules for the second messenger diacylglycerol
(DAG) or the phorbol esters. However, the individual contributions of these
tandem C1 domains to PKC function and, reciprocally, the influence of protein
context on their function remain uncertain. In the present study, we prepared
PKCδ constructs in which the individual C1a and C1b domains were
deleted, swapped, or substituted for one another to explore these issues. As
isolated fragments, both the δC1a and δC1b domains potently bound
phorbol esters, but the binding of [3H]phorbol 12,13-dibutyrate
([3H]PDBu) by the δC1a domain depended much more on the
presence of phosphatidylserine than did that of the δC1b domain. In
intact PKCδ, the δC1b domain played the dominant role in
[3H]PDBu binding, membrane translocation, and down-regulation. A
contribution from the δC1a domain was nonetheless evident, as shown by
retention of [3H]PDBu binding at reduced affinity, by increased
[3H]PDBu affinity upon expression of a second δC1a domain
substituting for the δC1b domain, and by loss of persistent plasma
membrane translocation for PKCδ expressing only the δC1b domain,
but its contribution was less than predicted from the activity of the isolated
domain. Switching the position of the δC1b domain to the normal position
of the δC1a domain (or vice versa) had no apparent effect on the
response to phorbol esters, suggesting that the specific position of the C1
domain within PKCδ was not the primary determinant of its activity.One of the essential steps for protein kinase C
(PKC)2 activation is
its translocation from the cytosol to the membranes. For conventional
(α, βI, βII, and γ) and novel (δ, ε, η,
and θ) PKCs, this translocation is driven by interaction with the
lipophilic second messenger sn-1,2-diacylglycerol (DAG), generated
from phosphatidylinositol 4,5-bisphosphate upon the activation of
receptor-coupled phospholipase C or indirectly from phosphatidylcholine via
phospholipase D (1). A pair of
zinc finger structures in the regulatory domain of the PKCs, the
“C1” domains, are responsible for the recognition of the DAG
signal. The DAG-C1 domain-membrane interaction is coupled to a conformational
change in PKC, both causing the release of the pseudosubstrate domain from the
catalytic site to activate the enzyme and triggering the translocation to the
membrane (2). By regulating
access to substrates, PKC translocation complements the intrinsic enzymatic
specificity of PKC to determine its substrate profile.The C1 domain is a highly conserved cysteine-rich motif (∼50 amino
acids), which was first identified in PKC as the interaction site for DAG or
phorbol esters (3). It
possesses a globular structure with a hydrophilic binding cleft at one end
surrounded by hydrophobic residues. Binding of DAG or phorbol esters to the C1
domain caps the hydrophilic cleft and forms a continuous hydrophobic surface
favoring the interaction or penetration of the C1 domain into the membrane
(4). In addition to the novel
and classic PKCs, six other families of proteins have also been identified,
some of whose members possess DAG/phorbol ester-responsive C1 domains. These
are the protein kinase D (5),
the chimaerin (6), the munc-13
(7), the RasGRP (guanyl
nucleotide exchange factors for Ras and Rap1)
(8), the DAG kinase
(9), and the recently
characterized MRCK (myotonic dystrophy kinase-related
Cdc42-binding kinase) families
(10). Of these C1
domain-containing proteins, the PKCs have been studied most extensively and
are important therapeutic targets
(11). Among the drug
candidates in clinical trials that target PKC, a number such as bryostatin 1
and PEP005 are directed at the C1 domains of PKC rather than at its catalytic
site.Both the classic and novel PKCs contain in their N-terminal regulatory
region tandem C1 domains, C1a and C1b, which bind DAG/phorbol ester
(12). Multiple studies have
sought to define the respective roles of these two C1 domains in PKC
regulation, but the issue remains unclear. Initial in vitro binding
measurements with conventional PKCs suggested that 1 mol of phorbol ester
bound per mole of PKC
(13-15).
On the other hand, Stubbs et al., using a fluorescent phorbol ester
analog, reported that PKCα bound two ligands per PKC
(16). Further, site-directed
mutagenesis of the C1a and C1b domains of intact PKCα indicated that the
C1a and C1b domains played equivalent roles for membrane translocation in
response to phorbol 12-myristate 13-acetate (PMA) and (-)octylindolactam V
(17). Likewise, deletion
studies indicated that the C1a and C1b domains of PKCγ bound PDBu
equally with high potency (3,
18). Using a functional assay
with PKCα expression in yeast, Shieh et al.
(19) deleted individual C1
domains and reported that C1a and C1b were both functional and equivalent upon
stimulation by PMA, with either deletion causing a similar reduction in
potency of response, whereas for mezerein the response depended essentially on
the C1a domain, with much weaker response if only the C1b domain was present.
Using isolated C1 domains, Irie et al.
(20) suggested that the C1a
domain of PKCα but not those of PKCβ or PKCγ bound
[3H]PDBu preferentially; different ligands showed a generally
similar pattern but with different extents of selectivity. Using synthesized
dimeric bisphorbols, Newton''s group reported
(21) that, although both C1
domains of PKCβII are oriented for potential membrane interaction, only
one C1 domain bound ligand in a physiological context.In the case of novel PKCs, many studies have been performed on PKCδ
to study the equivalency of the twin C1 domains. The P11G point mutation of
the C1a domain, which caused a 300-fold loss of binding potency in the
isolated domain (22), had
little effect on the phorbol ester-dependent translocation of PKCδ in
NIH3T3 cells, whereas the same mutation of the C1b caused a 20-fold shift in
phorbol ester potency for inducing translocation, suggesting a major role of
the C1b domain for phorbol ester binding
(23). A secondary role for the
C1a domain was suggested, however, because mutation in the C1a domain as well
as the C1b domain caused a further 7-fold shift in potency. Using the same
mutations in the C1a and C1b domains, Bögi et al.
(24) found that the binding
selectivity for the C1a and C1b domains of PKCδ appeared to be
ligand-dependent. Whereas PMA and the indole alkaloids indolactam and
octylindolactam were selectively dependent on the C1b domain, selectivity was
not observed for mezerein, the 12-deoxyphorbol 13-monoesters prostratin and
12-deoxyphorbol 13-phenylacetate, and the macrocyclic lactone bryostatin 1
(24). In in vitro
studies using isolated C1a and C1b domains of PKCδ, Cho''s group
(25) described that the two C1
domains had opposite affinities for DAG and phorbol ester; i.e. the
C1a domain showed high affinity for DAG and the C1b domain showed high
affinity for phorbol ester. No such difference in selectivity was observed by
Irie et al. (20).PKC has emerged as a promising therapeutic target both for cancer and for
other conditions, such as diabetic retinopathy or macular degeneration
(26-30).
Kinase inhibitors represent one promising approach for targeting PKC, and
enzastaurin, an inhibitor with moderate selectivity for PKCβ relative to
other PKC isoforms (but still with activity on some other non-PKC kinases) is
currently in multiple clinical trials. An alternative strategy for drug
development has been to target the regulatory C1 domains of PKC. Strong proof
of principle for this approach is provided by multiple natural products,
e.g. bryostatin 1 and PEP005, which are likewise in clinical trials
and which are directed at the C1 domains. A potential advantage of this
approach is the lesser number of homologous targets, <30 DAG-sensitive C1
domains compared with over 500 kinases, as well as further opportunities for
specificity provided by the diversity of lipid environments, which form a
half-site for ligand binding to the C1 domain. Because different PKC isoforms
may induce antagonistic activities, inhibition of one isoform may be
functionally equivalent to activation of an antagonistic isoform
(31).Along with the benzolactams
(20,
32), the DAG lactones have
provided a powerful synthetic platform for manipulating ligand: C1 domain
interactions (31). For
example, the DAG lactone derivative 130C037 displayed marked selectivity among
the recombinant C1a and C1b domains of PKCα and PKCδ as well as
substantial selectivity for RasGRP relative to PKCα
(33). Likewise, we have shown
that a modified DAG lactone (dioxolanones) can afford an additional point of
contact in ligand binding to the C1b domain of PKCδ
(34). Such studies provide
clear examples that ligand-C1 domain interactions can be manipulated to yield
novel patterns of recognition. Further selectivity might be gained with
bivalent compounds, exploiting the spacing and individual characteristics of
the C1a and C1b domains (35).
A better understanding of the differential roles of the two C1 domains in PKC
regulation is critical for the rational development of such compounds. In this
study, by molecularly manipulating the C1a or C1b domains in intact
PKCδ, we find that both the C1a and C1b domains play important roles in
PKCδ regulation. The C1b domain is predominant for ligand binding and
for membrane translocation of the whole PKCδ molecule. The C1a domain of
intact PKCδ plays only a secondary role in ligand binding but stabilizes
the PKCδ molecule at the plasma membrane for downstream signaling. In
addition, we show that the effect of the individual C1 domains of PKCδ
does not critically depend on their position within the regulatory domain. 相似文献
20.
Duvalius (sg. Neoduvalius) gejzadunayi
sp. n. from Pećina u Dubokom potoku cave ( Donje Biševo village near Rožaje, Montenegro), the first known representative of this subgenus from the territory of Montenegro is described, illustrated and compared with the related species of the subgenus Neoduvalius Müller, 1913. This new species is characterised by depigmented, medium sized body, totally reduced eyes, deep and complete frontal furrows, 3–4 pairs of discal setae in third elytral stria, as well as by the shape of aedeagus. Data on the distribution and the ecology of this remarkable species, as well as a check-list of the subgenus Neoduvalius are also provided. Recently described genera Serboduvalius Ćurčić, S. B. Pavićević & Ćurčić, B.P.M., 2001, Rascioduvalius Ćurčić, S. B. Brajković, Mitić & Ćurčić, B.P.M., 2003, Javorella Ćurčić, S. B. Brajković, Ćurčić, B.P.M. & Mitić, 2003 and Curcicia Ćurčić, S. B. & Brajković, 2003 are regarded as junior synonyms of the genus Duvalius Delarouzée. 相似文献