pH dependent stabilization of S2QA − and S2QB − charge pairs studied by thermoluminescence

The pH dependence of emission peak temperature and decay time of thermoluminescence arising from S₂Q_B ^– and S₂Q_A ^– recombinations demonstrates that a stabilization of S₂Q_B ^– occurs at low pH whereas stabilization of S₂Q_A ^– occurs at high pH. Based on comparative analysis of thermoluminescence parameters of the two types of recombination, we suggest that in the pH range between 5.3 and 7.5, E_m(S₂/S₁) and E_m(Q_A/Q_A ^–) are constant, but E_m(Q_B/Q_B ^–) gradually increases with decreasing pH, while in the pH range between 7.5 and 8.5, an unusual change occurs on S₂Q_A ^– charge pair, which is interpreted as either a decrease in E_m(S₂/S₁) or an increase in E_m(Q_A/Q_A ^–).     

Positions of the cytoplasmic end of BK α S0 helix relative to S1–S6 and of β1 TM1 and TM2 relative to S0–S6

The large-conductance, voltage- and Ca²⁺-gated K⁺ (BK) channel consists of four α subunits, which form a voltage- and Ca²⁺-gated channel, and up to four modulatory β subunits. The β1 subunit is expressed in smooth muscle, where it slows BK channel kinetics and shifts the conductance–voltage (G-V) curve to the left at [Ca²⁺] > 2 µM. In addition to the six transmembrane (TM) helices, S1–S6, conserved in all voltage-dependent K⁺ channels, BK α has a unique seventh TM helix, S0, which may contribute to the unusual rightward shift in the G-V curve of BK α in the absence of β1 and to a leftward shift in its presence. Such a role is supported by the close proximity of S0 to S3 and S4 in the voltage-sensing domain. Furthermore, on the extracellular side of the membrane, one of the two TM helices of β1, TM2, is adjacent to S0. We have now analyzed induced disulfide bond formation between substituted Cys residues on the cytoplasmic side of the membrane. There, in contrast, S0 is closest to the S2–S3 loop, from which position it is displaced on the addition of β1. The cytoplasmic ends of β1 TM1 and TM2 are adjacent and are located between the S2–S3 loop of one α subunit and S1 of a neighboring α subunit and are not adjacent to S0; i.e., S0 and TM2 have different trajectories through the membrane. In the absence of β1, 70% of disulfide bonding of W43C (S0) and L175C (S2–S3) has no effect on V₅₀ for activation, implying that the cytoplasmic end of S0 and the S2–S3 loop move in concert, if at all, during activation. Otherwise, linking them together in one state would obstruct the transition to the other state, which would certainly change V₅₀.     

Characterization and Genetic Study of the Ovine α S2 -Casein (CSN1S2) Allele B

An interesting and quite complex protein pattern has been described at ovine milk proteins but the genetic control of the variation observed was assessed only in few cases. The aim of this work was to characterize the ovine α _s2 -casein (CSN1S2) B variant, first observed in the Italian Gentile di Puglia, a fine-wooled ovine breed, and to investigate its occurrence in two further breeds, the Sarda and Camosciata, which are the most widespread dairy breeds in Italy. The B variant differs from the most common form A with two amino acid exchanges: Asp₇₅ → Tyr₇₅ and Ile₁₀₅ → Val₁₀₅. The first substitution, resulting in a loss of a negative charge, is responsible for the higher isoelectric point of the B protein variant, which allows its detection by isoelectric focusing electrophoresis (IEF). The occurrence of CSN1S2*B in Sarda and Comisana was demonstrated. Since the Asp₇₅ → Tyr₇₅ substitution modifies the protein electric charge, milk properties may result affected to some extent.     

α2A-Adrenoceptor-specific Stimulation of [35S]GTPγS Binding to Membrane Preparations of Rat Frontal Cortex

Functional activation of α_2A adrenergic receptors in the crude membranes from rat frontal cortex was studied by a [³⁵S]-guanosine 5′-O-(γ-thiotriphosphate) ([³⁵S]GTPγS) binding assay. α_2A agonists UK14304 and guanfacine decreased the ability of GDP to compete with [³⁵S]GTPγS binding to the membranes and 0.1 mM GDP was found to be optimal for the following functional experiments. However, even after careful optimization of experimental conditions the specificity of ligands for rat α₂ adrenoceptors were not sufficient, as agonists as well as antagonists became activators of other signal transduction systems before achieving their maximal effect in the α_2A-adrenergic system. Only using compromising concentration of agonist (up to 1 μM UK14304) and antagonist (up to 1 μM RS79948) to inhibit agonist’s effect, allowed us to filtrate out α_2A specific effect for characterization of signal transduction in rat frontal cortex membranes for the comparison efficacies of this system for different animals from behavioral experiments.     

Inhibition of micro-RNA-induced RNA silencing by 2′-O-methyl oligonucleotides in Drosophila S2 cells

Summary More than 90 different micro-ribonucleic acid (miRNA) encoding genes have been identified in Drosophila, yet the function of only two of these, bantam and DmiR-14, has been elucidated. In an effort to develop a general strategy for the analysis of miRNA function in Drosophila, two procedures were developed, in a Schneider line 2 cell culture system, which may be adapted to that end. First, we show that endogenous miRNAs can partially inhibit the expression of a transiently transfected reporter gene that has been modified to contain sequences complementary to that miRNA in the 3′ UTR of a target messenger RNA (mRNA). Inhibition occurs by RNA interference (RNAi), which involves mRNA degradation. Second, we demonstrate that this miRNA-induced RNAi can be partially rescued with 2′-O-methyl oligonucleotides that contain sequences complementary to the cognate miRNA. We discuss how these techniques may be used, in vivo, both for localizing the tissue distribution of endogenous miRNAs during Drosophila development and identifying phenotypes associated with a loss of miRNA function.     

A mimotope of Pre－S2 region of surface angigen of viral hepatitis B screened by phage display

To acquire the phage-displayed mimotopes which mimic the specificity of hepatitis B virus surface antigen (HBsAg), a random peptide library expressing linear peptide with 12 amino acids in length were used to screen with the serum from a hepatitis B virus infected patient in the recovery phase. After 3 rounds of biopanning, the positive phages were confirmed by competitive ELISA using HBsAg/P33. Two phagotopes were identified and one of them was confirmed as mimotope by competition experiment. Based on the mimotpe, a multiple antigenic peptide with four branches was synthesized by solid phase peptide synthesis. The antiginicity and specificity of the synthesized antigen was tested in BALB/c mice compared with the native epitope-based antigen. The results showed that the mimotope-based antigen could evoke higher titer of antibodies with the same specificity of the epitope-based antigen. Those findings indicate mimotopes can be used in antigen and vaccine design.     

The structure of Ca2+-loaded S100A2 at 1.3-Å resolution

S100A2 is an EF-hand calcium ion (Ca(2+))-binding protein that activates the tumour suppressor p53. In order to understand the molecular mechanisms underlying the Ca(2+) -induced activation of S100A2, the structure of Ca(2+)-bound S100A2 was determined at 1.3 ? resolution by X-ray crystallography. The structure was compared with Ca(2+) -free S100A2 and with other S100 proteins. Binding of Ca(2+) to S100A2 induces small structural changes in the N-terminal EF-hand, but a large conformational change in the C-terminal EF-hand, reorienting helix III by approximately 90°. This movement is accompanied by the exposure of a hydrophobic cavity between helix III and helix IV that represents the target protein interaction site. This molecular reorganization is associated with the breaking and new formation of intramolecular hydrophobic contacts. The target binding site exhibits unique features; in particular, the hydrophobic cavity is larger than in other Ca(2+)-loaded S100 proteins. The structural data underline that the shape and size of the hydrophobic cavity are major determinants for target specificity of S100 proteins and suggest that the binding mode for S100A2 is different from that of other p53-interacting S100 proteins. Database Structural data are available in the Protein Data Bank database under the accession number 4DUQ     

In Vitro Characterization of Echinomycin Biosynthesis: Formation and Hydroxylation of L-Tryptophanyl-S-Enzyme and Oxidation of (2S,3S) β-Hydroxytryptophan

Quinoxaline-2-carboxylic acid (QXC) and 3-hydroxyquinaldic acid (HQA) feature in quinomycin family and confer anticancer activity. In light of the significant potency against cancer, the biosynthetic gene clusters have been reported from many different Streptomyces strains, and the biosynthetic pathway were proposed mainly based on the in vivo feeding experiment with isotope labeled putative intermediates. Herein we report another gene cluster from Streptomyces griseovariabilis subsp. bandungensis subsp. nov responsible for the biosynthesis of echinomycin (a member of quinomycin family, also named quinomycin A) and presented in vitro evidence to corroborate the previous hypothesis on QXC biosynthesis, showing that only with the assistance of a MbtH-like protein Qui5, did the didomain NRPS protein (Qui18) perform the loading of a L-tryptophan onto its own PCP domain. Particularly, it was found that Qui5 and Qui18 subunits form a functional tetramer through size exclusion chromatography. The subsequent hydroxylation on β-carbon of the loaded L-tryptophan proved in vitro to be completed by cytochrome P450-dependent hydroxylase Qui15. Importantly, only the Qui18 loaded L-tryptophan can be hydroxylated by Qui15 and the enzyme was inactive on free L-tryptophan. Additionally, the chemically synthesized (2S,3S) β-hydroxytryptophan was detected to be converted by the tryptophan 2,3-dioxygenase Qui17 through LC-MS, which enriched our previous knowledge that tryptophan 2,3-dioxygenase nearly exclusively acted on L-tryptophan and 6-fluoro-tryptophan.     

The B56γ3 Regulatory Subunit of Protein Phosphatase 2A (PP2A) Regulates S Phase-specific Nuclear Accumulation of PP2A and the G1 to S Transition

Protein phosphatase 2A (PP2A) is a heterotrimeric enzyme consisting of a scaffold subunit (A), a catalytic subunit (C), and a variable regulatory subunit (B). The regulatory B subunits determine the substrate specificity and subcellular localization of the PP2A holoenzyme. Here, we demonstrate that the subcellular localization of the B56γ3 regulatory subunit is regulated in a cell cycle-specific manner. Notably, B56γ3 becomes enriched in the nucleus at the G₁/S border and in S phase. The S phase-specific nuclear enrichment of B56γ3 is accompanied by increases of nuclear A and C subunits and nuclear PP2A activity. Overexpression of B56γ3 promotes nuclear localization of the A and C subunits, whereas silencing both B56γ2 and B56γ3 blocks the S phase-specific increase in the nuclear localization and activity of PP2A. In NIH3T3 cells, B56γ3 overexpression reduces p27 phosphorylation at Thr-187, concomitantly elevates p27 protein levels, delays the G₁ to S transition, and retards cell proliferation. Consistently, knockdown of endogenous B56γ3 expression reduces p27 protein levels and increases cell proliferation in HeLa cells. These findings demonstrate that the dynamic nuclear distribution of the B56γ3 regulatory subunit controls nuclear PP2A activity, which regulates cell cycle controllers, such as p27, to restrain cell cycle progression, and may be responsible for the tumor suppressor function of PP2A.     

Fate of the (2Fe-2S)(2+) cluster of Escherichia coli biotin synthase during reaction: a Mössbauer characterization

Biotin synthase, the enzyme which catalyzes the last step of the biosynthesis of biotin, contains only (2Fe-2S)(2+) clusters when isolated under aerobic conditions. Previous results showed that reduction by dithionite or photoreduced deazaflavin converts the (2Fe-2S)(2+) to (4Fe-4S)(2+,+). However, until now, no detailed investigation concerning the fate of the (2Fe-2S)(2+) during reduction under assay conditions (NADPH, flavodoxin, flavodoxin reductase) has been realized. Here, we show by M?ssbauer spectroscopy on a partially purified fraction overexpressing the enzyme that, in the presence of a S(2)(-) source and Fe(2+), there is conversion of the predominant (2Fe-2S)(2+) clusters into a 1:1 mixture of (2Fe-2S)(2+) and (4Fe-4S)(2+). No change in this cluster composition was observed in the presence of the physiological reducing system. When the reaction was allowed to proceed by addition of the substrate dethiobiotin, the (4Fe-4S)(2+) was untouched whereas the (2Fe-2S)(2+) was degraded into a new species. This is consistent with the hypothesis that the reduced (4Fe-4S) cluster is involved in mediating the cleavage of AdoMet and that the (2Fe-2S)(2+) is the sulfur source for biotin.     

Conformational Change of the Rieske [2Fe–2S] Protein inCytochrome bc 1 Complex

Structures of mitochondrial bc ₁ complex have been reported based on four different crystalforms by three different groups. In these structures, the extrinsic domain of the Rieske [2Fe–2S]protein, surprisingly, appeared at three different positions: the c ₁ position, where the [2Fe–2S]cluster exists in close proximity to the heme c ₁; the b position, where the [2Fe–2S] clusterexist in close proximity to the cytochrome b; and the intermediate position where the[2Fe–2S] cluster exists in between c ₁ and b positions. The conformational changes betweenthese three positions can be explained by a combination of two rotations; (1) a rotation of theentire extrinsic domain and (2) a relative rotation between the cluster-binding fold and thebase fold within the extrinsic domain. The hydroquinone oxidation and the electron bifurcationmechanism at the Q_P binding pocket of the bc ₁ complex is well explained using theseconformational changes of the Rieske [2Fe–2S] protein.     

Norepinephrine Transporter Imaging in the Brain of a Rat Model of Depression Using Radioiodinated (2S, αS)-2-(α-(2-iodophenoxy)benzyl)morpholine

AbstractTo visualize the norepinephrine transporters (NETs) in various brain diseases, we developed radioiodinated (2S,αS)-2-(α-(2-iodophenoxy)benzyl)morpholine ((S,S)-IPBM). This radioligand achieved the basic requirements for NET imaging. In this study, we assessed the potential of radioiodinated (S,S)-IPBM as an imaging biomarker of NET to obtain diagnostic information about depression in relation to NET expression in the brain using a rat depression model. The ex vivo autoradiographic experiments using the (S,S)-[125I]IPBM showed significantly lower accumulation of radioactivity in the locus coeruleus (LC) and the anteroventricular thalamic nucleus (AVTN) of the depression group than in those of the control group. Consequently, in vitro autoradiographic experiments showed that NET maximum binding (Bmax) values in the LC and AVTN, known as NET-rich regions, were significantly decreased in the rat model of depression when compared to those of the control rats. In addition, there was an extremely good correlation between NET Bmax and (S,S)-IPBM accumulation (r = .98), an indication of radioiodinated IPBM as a quantitative NET imaging biomarker. The reduction in (S,S)-[125I]IPBM accumulation in the rat model of depression correlated with that of NET density. These results suggest that (S,S)-[123I]IPBM has potential as an imaging biomarker of NET to obtain diagnostic information about major depression.     

Synthesis of (2′S)-1-(2-C-Azidomethyl-2-deoxy and 2-C-Cyanomethyl-2-deoxy-β-D-arabinofuranosyl)cytosines

Abstract

2′-C-Cyanomethyl-2′-deoxy-arabinosylcytosine 3 and 2′-C-azidomethyl-2′-deoxy-arabinosylcytosine 4 were synthesized from uridine. The antineoplastic activities of these compounds were evaluated.     

Metabolic profiling of HepG2 cells incubated with S(?) and R(+) enantiomers of anti-coagulating drug warfarin

Warfarin is a commonly prescribed oral anticoagulant with narrow therapeutic index. It achieves anti-coagulating effects by interfering with the vitamin K cycle. Warfarin has two enantiomers, S(−) and R(+) and undergoes stereoselective metabolism, with the S(−) enantiomer being more effective. We reported the intracellular metabolic profile in HepG2 cells incubated with S(−) and R(+) warfarin by GCMS. Chemometric method PCA was applied to analyze the individual samples. A total of 80 metabolites which belong to different categories were identified. Two batches of experiments (with and without the presence of vitamin K) were designed. In samples incubated with S(−) and R(+) warfarin, glucuronic acid showed significantly decreased in cells incubated with R(+) warfarin but not in those incubated with S(−) warfarin. It may partially explain the lower bio-activity of R(+) warfarin. And arachidonic acid showed increased in cells incubated with S(−) warfarin but not in those incubated with R(+) warfarin. In addition, a number of small molecules involved in γ-glutamyl cycle displayed ratio variations. Intracellular glutathione detection further validated the results. Taken together, our findings provided molecular evidence on a comprehensive metabolic profile on warfarin-cell interaction which may shed new lights on future improvement of warfarin therapy.     

Microparticle bombardment of Stylosanthes guianensis: transformation parameters and expression of a methionine-rich 2S albumin gene

An effective protocol to generate stable transformants of the tropical forage legume Stylosanthes guianensis (Aubl.) Sw. in a selection-free system was developed. Based on transient reporter gene expression, we have obtained transformation rates of 3.47% using 30-day-old calli as target, 1300 psi helium pressure, 12.5 cm microprojectile flight distance, 10–20 mm distance between macrocarrier membrane and stopping screen and 10–20 mm gap distance between the shock wave generator and the macrocarrier. These parameters were utilized to produce transgenic S. guianensis plants expressing Be2S1 from Bertholletia excelsa that codes for a methionine-rich storage protein driven by a green-tissue specific promoter, Ats1 from Arabidopsis thaliana. Transgenic plants were identified by a PCR-based high-throughput screen in a selective agent-free system, employing pools of 20–50 regenerating shoots. The integration of the exogenous gene in the host genome was confirmed by Southern blot analysis of PCR-positive plants. The expression of the introduced gene was confirmed in leaf tissue of transgenic plants by Northern and Western blot analyses. Immunoblots of cellular fractions showed that BE2S1 expressed in Stylosanthes is mainly targeted to the vacuoles.     

Termination of molar pregnancy by intramuscular administration of 15(S)-15-methyl-prostaglandin F2α

Eleven patients entered a multicentre trial of repeated intramuscular injections of 15(S)-15-methyl-prostaglandin F2α (15-me-PGF2α) for terminating molar pregnancy. Duration of pregnancy ranged from 9 to 24 (median: 16) weeks and uterine size from 15 to 24 (median: 19) weeks. Complete (n=5) or incomplete (n=4) expulsion of molar tissue occurred in 9 patients (82%) after a median duration of 15.7 hours. In the remaining 2 patients treatment was interrupted after 8 hours at a cervical dilatation of 1 cm or more. Gastro-intestinal side effects were prominent in 64%. The use of prostaglandins in the management of hydatidiform mole is discussed.     

β2-Strand of salivary S cystatins: A “chemeleon sequence”

Secondary structure prediction of salivary cystatins S, SA, and SN carried out by several methods label the 39-58 sequence (β2-strand) as predominantly α-helical. The helical propensity of a peptide corresponding to β2-strand of salivary SA cystatin analyzed by CD display high helical propensity in aqueous solution, whereas peptides matching the β2-strand amino acid sequence of cystatins S and SN, display random coil conformation in aqueous solution but acquire α-helical conformation in the presence of trifluoroethanol (TFE). Moreover molecular dynamics simulation performed on the homology modeling of cystatin SA constructed on the basis of recently determined three-dimensional structure of salivary cystatin D, suggests that cystatin SA does not significantly deviate from the starting structure over the course of the simulation. The results obtained indicate that the β2-strand of salivary S cystatins has high helical propensity when isolated from native protein and acquire the final β structure by interaction with the rest of the polypeptide chain.