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991.
Where the fish swim above the birds: configurations and challenges of wetland restoration in the Po Delta,Italy 下载免费PDF全文
Wetland and estuary restoration presents a number of complex challenges that are primarily social, cultural, economic, and governance‐related rather than ecological. Here we consider the case of wetland restoration in the Po Delta, Italy. Wetland restoration of the Po Delta is a goal of a broad range of actors in the region and this project is a response to local calls for action. We investigate why local stakeholders are unsatisfied with apparently successful restoration projects, and appraise the factors that favor both the fulfillment of environmental targets and establishment of cooperative relations. We suggest that historical legacies of land use in the Po Delta have influenced current governance practices in a complex and fragmented governance context. Also, patterns of wetland restoration and wetland management practices differ between wetland types, and their outcomes may be influenced by the number of stakeholders involved, funding, and ability to generate direct revenues from management. However, there seem to be no blueprint solutions to successful wetland management and wetland restoration, and results are uneven at the landscape scale and often depending on contingencies. Maintaining traditional practices that retain cultural importance may be seen as part of restoration by local people. As a landscape that is highly anthropogenic and in continuous motion, we argue that the Delta exemplifies some of the challenges that restoration will face in a world increasingly characterized by novel ecosystems. We suggest actions that could contribute to enhancing wetland restoration outcomes in the Po Delta. 相似文献
992.
Enzymatic recycling of ascorbic acid from dehydroascorbic acid by glutathione‐like peptides in the extracellular loops of aminergic G‐protein coupled receptors 下载免费PDF全文
Robert Root‐Bernstein Jenna Fewins Tyler Rhinesmith Ariana Koch Patrick F. Dillon 《Journal of molecular recognition : JMR》2016,29(7):296-302
The intracellular recycling of ascorbic acid from dehydroascorbic acid by the glutathione–glutathione reductase system has been well‐characterized. We propose that extracellular recycling of ascorbic acid is performed in a similar manner by cysteine‐rich, glutathione‐like regions of the first and second extracellular loops of some aminergic receptors including adrenergic, histaminergic, and dopaminergic receptors. Previous research in our laboratory demonstrated that ascorbic acid binds to these receptors at a site on their first or second extracellular loops, significantly enhancing ligand activity, and apparently recycling hundreds of times their own concentration of ascorbate in an enzymatic fashion. In this study, we have synthesized 25 peptides from the first and second extracellular loops of aminergic and insulin receptors and compared them directly to glutathione for their ability to prevent the oxidation of ascorbate and to regenerate ascorbate from dehydroascorbic acid. Peptide sequences that mimic glutathione in containing a cysteine and a glutamic acid‐like amino acid also mimic glutathione activity in effects and in kinetics. Some (but not all) peptide sequences that contain one or more methionines instead of cysteine can significantly retard the oxidation of ascorbic acid but do not recycle it from dehydroascorbate into ascorbate. Peptides lacking both cysteines and methionines uniformly failed to alter significantly ascorbate or dehydroascorbate oxidation or reduction. We believe that this is the first proof that receptors may carry out both ligand binding and enzymatic activity extracellularly. Our results suggest the existence of a previously unknown extracellular system for recycling ascorbate. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
993.
Vaisburg A Paquin I Bernstein N Frechette S Gaudette F Leit S Moradei O Raeppel S Zhou N Bouchain G Woo SH Jin Z Gillespie J Wang J Fournel M Yan PT Trachy-Bourget MC Robert MF Lu A Yuk J Rahil J Macleod AR Besterman JM Li Z Delorme D 《Bioorganic & medicinal chemistry letters》2007,17(24):6729-6733
A variety of N-(2-amino-phenyl)-4-(heteroarylmethyl)-benzamides were designed and synthesized. These compounds were shown to inhibit recombinant human HDAC1 with IC50 values in the sub-micromolar range. In human cancer cells growing in culture these compounds induced hyperacetylation of histones, induced the expression of the tumor suppressor protein p21WAF1/Cip1, and inhibited cellular proliferation. Certain compounds of this class also showed in vivo activity in various human tumor xenograft models in mice. 相似文献
994.
Exploring subdomain cooperativity in T4 lysozyme II: uncovering the C-terminal subdomain as a hidden intermediate in the kinetic folding pathway 下载免费PDF全文
Cellitti J Bernstein R Marqusee S 《Protein science : a publication of the Protein Society》2007,16(5):852-862
Intermediates along a protein's folding pathway can play an important role in its biology. Previous kinetics studies have revealed an early folding intermediate for T4 lysozyme, a small, well-characterized protein composed of an N-terminal and a C-terminal subdomain. Pulse-labeling hydrogen exchange studies suggest that residues from both subdomains contribute to the structure of this intermediate. On the other hand, equilibrium native state hydrogen experiments have revealed a high-energy, partially unfolded form of the protein that has an unstructured N-terminal subdomain and a structured C-terminal subdomain. To resolve this discrepancy between kinetics and equilibrium data, we performed detailed kinetics analyses of the folding and unfolding pathways of T4 lysozyme, as well as several point mutants and large-scale variants. The data support the argument for the presence of two distinct intermediates, one present on each side of the rate-limiting transition state barrier. The effects of circular permutation and site-specific mutations in the wild-type and circular permutant background, as well as a fragment containing just the C-terminal subdomain, support a model for the unfolding intermediate with an unfolded N-terminal and a folded C-terminal subdomain. Our results suggest that the partially unfolded form identified by native state hydrogen exchange resides on the folded side of the rate-limiting transition state and is, therefore, under most conditions, a "hidden" intermediate. 相似文献
995.
Contiguous patterns of c-kit and steel expression: analysis of mutations at the W and Sl loci. 总被引:13,自引:0,他引:13
B Motro D van der Kooy J Rossant A Reith A Bernstein 《Development (Cambridge, England)》1991,113(4):1207-1221
Mutations in either the dominant white-spotting (W) or Steel (Sl) loci of the mouse lead to coat color, primordial germ cell and hematopoietic defects. Consistent with the cell autonomous and microenvironmental nature of W and Sl mutations, respectively, it has recently been shown that W encodes the c-kit receptor tyrosine kinase while Sl encodes a ligand for this receptor. Previous in situ hybridization analysis has shown that both c-kit and steel are expressed in the embryo in anatomical sites known to be affected by W and Sl mutations and in various tissues in which no corresponding phenotype has been described. To investigate the possible involvement of the Kit transduction pathway in developmental processes, we compared the patterns of expression of c-kit and steel in wild-type embryos and in embryos homozygous for severe (lethal) and mild (viable) alleles at the W and Sl loci. In addition, we analyzed the patterns of expression of both genes in adult wild-type and mutant gonads and brain. Both c-kit and steel are contiguously expressed in a wide variety of anatomical locations in both the developing embryo and in the adult. In adult gonads, steel is expressed in the follicular cells of the ovary and in Sertoli cells of the testis, the layers that immediately surround the c-kit expressing germ cells. In adult brain, the complementary patterns are particularly striking in the olfactory bulb, cerebral cortex, hippocampus region and cerebellum. steel expression in brain is probably restricted to neurons in certain areas, while c-kit is expressed in neurons and in some glial cells. Severe mutations in the W or Sl loci result in dramatic reduction or absence of c-kit positive cells in lineages known to be affected by these mutations. In contrast, these mutations do not affect the number or histological organization of c-kit positive cells in the embryonic peripheral or central nervous systems, nor is the number or organization of c-kit positive cells detectably altered in Wv/Wv or Sld/Sld adult brain. Taken together, these results suggest that the Kit signaling pathway is not obligatory for the viability and/or migration of most c-kit expressing cells either because of functional redundancy with another signaling pathway or because the Kit pathway is involved in post-developmental processes of mature cells. 相似文献
996.
997.
Karen HS Wilson 《BMC evolutionary biology》2009,9(1):243-26
Background
Neurotrophins and their Trk and p75NTR receptors play an important role in the nervous system. To date, neurotrophins, Trk and p75NTR have only been found concomitantly in deuterostomes. In protostomes, homologues to either neurotrophin, Trk or p75NTR are reported but their phylogenetic relationship to deuterostome neurotrophin signaling components is unclear. Drosophila has neurotrophin homologues called Spätzles (Spz), some of which were recently renamed neurotrophins, but direct proof that these are deuterostome neurotrophin orthologues is lacking. Trks belong to the receptor tyrosine kinase (RTK) family and among RTKs, Trks and RORs are closest related. Flies lack Trks but have ROR and ROR-related proteins called NRKs playing a neurotrophic role. Mollusks have so far the most similar proteins to Trks (Lymnaea Trk and Aplysia Trkl) but the exact phylogenetic relationship of mollusk Trks to each other and to vertebrate Trks is unknown. p75NTR belongs to the tumor necrosis factor receptor (TNFR) superfamily. The divergence of the TNFR families in vertebrates has been suggested to parallel the emergence of the adaptive immune system. Only one TNFR representative, the Drosophila Wengen, has been found in protostomes. To clarify the evolution of neurotrophin signaling components in bilateria, this work analyzes the genome of the crustacean Daphnia pulex as well as new genetic data from protostomes.Results
The Daphnia genome encodes a neurotrophin, p75NTR and Trk orthologue together with Trkl, ROR, and NRK-RTKs. Drosophila Spz1, 2, 3, 5, 6 orthologues as well as two new groups of Spz proteins (Spz7 and 8) are also found in the Daphnia genome. Searching genbank and the genomes of Capitella, Helobdella and Lottia reveals neurotrophin signaling components in other protostomes.Conclusion
It appears that a neurotrophin, Trk and p75NTR existed at the protostome/deuterostome split. In protostomes, a "neurotrophin superfamily" includes Spzs and neurotrophins which respectively form two paralogous families. Trks and Trkl proteins also form closely related paralogous families within the protostomian RTKs, whereby Trkls are absent in deuterostomes. The finding of p75NTR in several protostomes suggests that death domain TNFR superfamily proteins appeared early in evolution. 相似文献998.
Recent studies have shown that cytoplasmic proteins are exported
efficiently in Escherichia coli only if they are attached to signal
peptides that are recognized by the signal recognition particle and are
thereby targeted to the SecYEG complex cotranslationally. The evidence
suggests that the entry of these proteins into the secretory pathway at an
early stage of translation is necessary to prevent them from folding into a
translocation-incompetent conformation. We found, however, that several
glycolytic enzymes attached to signal peptides that are recognized by the
signal recognition particle were exported inefficiently. Based on previous
studies of post-translational export, we hypothesized that the export block
was due to the presence of basic residues at the extreme N terminus of each
enzyme. Consistent with our hypothesis, we found that the introduction of
negatively charged residues into this segment increased the efficiency of
export. Export efficiency was sensitive to the number, position, and sequence
context of charged residues. The importance of charge for efficient export was
underscored by an in silico analysis that revealed a conserved
negative charge bias at the N terminus of the mature region of bacterial
presecretory proteins. Our results demonstrate that cotranslational targeting
of a protein to the E. coli SecYEG complex does not ensure its export
but that export also depends on a subsequent event (most likely the initiation
of translocation) that involves sequences both within and just beyond the
signal peptide.Since the “signal hypothesis” was proposed over 30 years ago
(1), it has become clear that
signal sequences are not simply generic hydrophobic peptides that earmark
proteins for secretion. In bacteria, the features of a signal peptide
determine the mechanism by which a given presecretory protein is targeted to
the SecYEG translocation complex in the inner membrane
(IM).2 Whereas most or
all signal peptides are recognized by the signal recognition particle (SRP) in
mammalian cells, only a small fraction of Escherichia coli signal
peptides are recognized by SRP. These signal peptides are typically extremely
hydrophobic (2,
3), but SRP apparently can also
recognize slightly less hydrophobic signal peptides that contain a highly
basic N terminus (4). SRP
recognizes signal peptides as they emerge from translating ribosomes and then
targets ribosome-nascent chain complexes to the IM cotranslationally
(5). The binding of SRP to its
receptor (FtsY), which interacts with the SecYEG complex
(6), leads to the release of
the nascent chain in the immediate vicinity of the translocation machinery. By
targeting nascent polypeptides to the SecYEG complex at an early stage of
translation, SRP prevents its substrates from folding into a conformation that
is incompatible with translocation through the narrow channel formed by the
SecYEG complex (7). Because
most signal peptides are not recognized by E. coli SRP, the majority
of presecretory proteins are fully synthesized and targeted
post-translationally to the IM. These proteins are maintained in a
translocation-competent conformation by molecular chaperones such as SecB that
keep them unfolded (or loosely folded)
(8). Signal peptides themselves
also appear to play a role in maintaining translocation competence
(9,
10). After mediating the
targeting reaction, signal peptides likely play a role in gating open the
SecYEG complex to initiate translocation.Interestingly, although signal sequences are the most salient feature of
presecretory proteins, they are neither completely necessary nor sufficient to
mediate protein export in E. coli
(11–13).
A version of alkaline phosphatase that lacks a signal peptide is still
exported, albeit very inefficiently
(11). The export of the
leaderless protein, unlike the export of wild-type alkaline phosphatase, is
strictly dependent on SecB
(11). Conversely, the
attachment of signal peptides to cytoplasmic proteins often does not promote
their export (14). In light of
evidence that folding and export are competing events, these observations led
to the proposal that exported proteins tend to fold slowly (or are prevented
from folding by chaperones) and therefore remain translocation-competent even
without a signal peptide, whereas cytoplasmic proteins fold rapidly into a
conformation that is incompatible with export. Recent studies that used
thioredoxin as a model protein have validated this hypothesis. Whereas the
wild-type protein attached to a typical signal peptide remained trapped in the
cytoplasm, four of five slow folding mutants were exported efficiently
(15). Furthermore, attachment
of a signal peptide that is recognized by SRP to thioredoxin led to efficient
export (16). This idea was
further confirmed by a report in which various DARPins (designed
ankyrin Repeat proteins) were
attached to different signal peptides. Most of the DARPins were exported
efficiently when they were fused to signal peptides that mediate
cotranslational targeting but remained in the cytoplasm when they were
attached to signal peptides that are bypassed by SRP
(17).Despite these observations, there are several lines of evidence suggesting
that export efficiency is not simply dictated by the ability of a protein to
reach the SecYEG complex before folding into a translocation-incompetent
conformation. For reasons that are unclear, some DARPins are secreted
inefficiently even when they are routed into the SRP pathway
(17). In addition, numerous
reports have indicated that the amino acid composition of the segment of
post-translationally targeted presecretory proteins that lies just beyond the
signal peptide cleavage site has a dramatic effect on export efficiency.
Statistical analysis has shown that the first ∼5–15 residues of the
mature region of most presecretory proteins produced by Gram-negative bacteria
is neutral or has a net negative charge
(18). Consistent with the
observed sequence bias, the presence of multiple basic residues at the N
terminus of the mature region often leads to accumulation of the secretory
precursor, whereas conversion of the basic residues to acidic residues
restores export
(19–22).
Because different combinations of proteins and signal peptides were used in
these studies, the exact number and location of charged residues that impinge
on the efficiency of export is unclear. In any case, the effect of the net
charge in the region distal to the signal peptide on protein export has never
been explained. Although basic residues might conceivably promote premature
folding of presecretory proteins or block the cleavage of signal peptides by
leader peptidase, it is also possible that they inhibit an uncharacterized
post-targeting event. Even if effects on signal peptide cleavage could have
been ruled out in the aforementioned studies, however, it would not have been
possible to distinguish between effects on protein folding and effects on a
hypothetical post-targeting step because only proteins that are targeted
post-translationally were monitored.To gain further insight into the factors that govern the efficiency of
protein export, we sought an explanation for the observation that the
cotranslational targeting of at least some cytoplasmic proteins is
insufficient to guarantee their translocation across the IM. We found that the
export of several different endogenous E. coli cytoplasmic proteins
required not only the attachment of a signal peptide that is recognized by SRP
but also a net negative charge just past the signal peptide cleavage site.
Taken together with previous results, our data show that the charge of the
segment just beyond the signal peptide influences export efficiency
irrespective of the mechanism by which a protein is targeted to the IM.
Because proteins that are targeted cotranslationally reach the IM before they
have a chance to fold, our results imply the existence of a post-targeting
step (most likely the initiation of translocation) that is facilitated by
acidic residues distal to the signal peptide and inhibited or delayed by basic
residues. These results help to resolve a long-standing puzzle about the
influence of the mature region of presecretory proteins on protein export and
have significant implications for optimizing the export of cytosolic and
heterologous proteins in E. coli. 相似文献
999.
Jan Lukáš Carlos Bernstein Hainan Gu Silvia Dorn 《Entomologia Experimentalis et Applicata》2010,136(1):80-88
In the parasitoid Venturia canescens Gravenhorst (Hymenoptera: Ichneumonidae), asexual and sexual wasps coexist in the field in the Mediterranean basin, but only the asexual strain is present indoors. The sexual strain dominates outdoors despite the demographic costs associated with the production of males and mate location. The present study tests whether females of the sexual and asexual strains of V. canescens differ in flight characteristics in line with the differences of their preferred habitats and enquires whether these differences might contribute to the persistence of sexually reproducing individuals in the vicinity of asexual counterparts. The results show that sexual female wasps are smaller than their asexual counterparts. The size of wasps has a strong influence on flight parameters, with larger animals generally being better fliers. In wasps of approximately the same size, sexual wasps fly faster than their asexual counterparts under experimental laboratory conditions, in terms of both the average speed over the observation period as well as the longest single flight. Sexual wasps also perform fewer flights to cover the same distance. Sexual wasps have higher wing loading than asexual ones of the same size, which could have contributed to the observed differences in speed between individuals of both reproductive modes. There are no significant differences between the two reproductive modes in the parameters related to the distance traversed or the time spent in flight. This study shows clear differences in the flight behaviour of sexual and asexual V. canescens. Together with previous results, this finding suggests differential adaptations to their preferred habitats. These differences might ease the competition between modes of reproduction through niche and habitat differentiation and might help to explain their coexistence on a geographical scale. 相似文献
1000.
Supriya D. Mahajan Anardi Agosto-Mojica Jessica L. Reynolds Donald E. Sykes Joshua Adams Zale Bernstein Stanley A. Schwartz 《Biochemical and biophysical research communications》2010,396(2):348-352
Allelic variants of the genes for chemokine receptors and their natural ligands, the chemokines, and cytokines can affect HIV-1 disease progression. This study investigates the level of expression of the CCR5-Δ32, CCR2b-641, RANTES In1.1C, SDF-1 3′A, IL-10-5′-592A and IL-4-589T alleles in two unique HIV-1 infected patient cohorts that represent the two distinct stages of disease progression, namely rapid progressors (RPs) and long term non-progressors (LTNPs) (n = 12/group) were recruited. Quantitation of the gene expression of CCR5-Δ32, CCR2b-641, RANTES In1.1C, SDF-1 3′A, IL-10-5′−592A and IL-4-589T in peripheral blood mononuclear leukocytes (PBML) isolated from patients was performed by real time, quantitative (Q)-PCR using DNA was isolated from PBML. We observed that expression of these HIV-protective alleles was generally greater in the LTNP cohort than the RP cohort. LTNPs expressed more of the protective chemokine, SDF-1α than RPs, and no statistically significant difference was observed in RANTES production between the LTNPs and RPs. The LTNPs expressed significantly less amounts of cytokines IL-10 and IL-4 as compared to the RPs. Our results demonstrate that gene polymorphisms for CCR5-Δ32, CCR2b-641, RANTES In1.1C, SDF-1 3′A, IL-10-5′−592A and IL-4-589T may be used as clinical markers to predict progression of HIV-1 infections. 相似文献