One gene, two diseases and three conformations: molecular dynamics simulations of mutants of human prion protein at room temperature and elevated temperatures

Fatal familial insomnia (FFI) and Creutzfeldt-Jakob disease (CJD) are associated to the same mutation at codon 178 but differentiate into clinicopathologically distinct diseases determined by this mutation and a naturally occurring methionine-valine polymorphism at codon 129 of the prion protein gene. It has been suggested that the clinical and pathological difference between FFI and CJD is caused by different conformations of the prion protein. Using molecular dynamics (MD), we investigated the effect of the mutation at codon 178 and the polymorphism at codon 129 on prion protein dynamics and conformation at normal and elevated temperatures. Four model structures were examined with a focus on their dynamics and conformational changes. The results showed differences in stability and dynamics between polymorphic variants. Methionine variants demonstrated a higher stability than valine variants. Elongation of existing beta-sheets and formation of new beta-sheets was found to occur more readily in valine polymorphic variants. We also discovered the inhibitory effect of proline residue on existing beta-sheet elongation.     

New spectrophotometric methods for the determination of nifedipine in pharmaceutical formulations

Two simple, sensitive and economical spectrophotometric methods were developed for the determination of nifedipine in pharmaceutical formulations. Method A is based on the reaction of the nitro group of the drug with potassium hydroxide in dimethyl sulphoxide (DMSO) medium to form a coloured product, which absorbs maximally at 430 nm. Method B uses oxidation of the drug with ammonium molybdate and subsequently reduced molybdenum blue is measured at 830 nm. Beer's law is obeyed in the concentration range of 5.0-50.0 and 2.5-45.0 microg ml(-1) with methods A and B, respectively. Both methods have been successfully applied for the assay of the drug in pharmaceutical formulations. No interference was observed from common pharmaceutical adjuvants. The reliability and the performance of the proposed methods are established by point and interval hypothesis tests and through recovery studies.     

Cross-desensitization among CXCR1, CXCR2, and CCR5: role of protein kinase C-epsilon

The IL-8 (or CXCL8) chemokine receptors, CXCR1 and CXCR2, activate protein kinase C (PKC) to mediate leukocyte functions. To investigate the roles of different PKC isoforms in CXCL8 receptor activation and regulation, human mononuclear phagocytes were treated with CXCL8 or CXCL1 (melanoma growth-stimulating activity), which is specific for CXCR2. Plasma membrane association was used as a measure of PKC activation. Both receptors induced time-dependent association of PKCalpha, -beta1, and -beta2 to the membrane, but only CXCR1 activated PKCepsilon. CXCL8 also failed to activate PKCepsilon in RBL-2H3 cells stably expressing CXCR2. DeltaCXCR2, a cytoplasmic tail deletion mutant of CXCR2 that is resistant to internalization, activated PKCepsilon as well as CXCR1. Expression of the PKCepsilon inhibitor peptide epsilonV1 in RBL-2H3 cells blocked PKCepsilon translocation and inhibited receptor-mediated exocytosis, but not phosphoinositide hydrolysis or peak intracellular Ca(2+) mobilization. epsilonV1 also inhibited CXCR1-, CCR5-, and DeltaCXCR2-mediated cross-regulatory signals for GTPase activity, Ca(2+) mobilization, and internalization. Peritoneal macrophages from PKCepsilon-deficient mice (PKCepsilon(-/-)) also showed decreased CCR5-mediated cross-desensitization of G protein activation and Ca(2+) mobilization. Taken together, the results indicate that CXCR1 and CCR5 activate PKCepsilon to mediate cross-inhibitory signals. Inhibition or deletion of PKCepsilon decreases receptor-induced exocytosis and cross-regulatory signals, but not phosphoinositide hydrolysis or peak intracellular Ca(2+) mobilization, suggesting that cross-regulation is a Ca(2+)-independent process. Because DeltaCXCR2, but not CXCR2, activates PKCepsilon and cross-desensitizes CCR5, the data further suggest that signal duration leading to activation of novel PKC may modulate receptor-mediated cross-inhibitory signals.     

Model complexes for amavadine,a vanadium natural product

Amavadine is a vanadium natural product from the mushroom Amanita muscaria. Earlier reports have characterized the compound as a vanadyl (VO²⁺) complex with two N-hydroxy-αα-iminodipropionic acid ligands, but no hypothesis as to its function has yet been put forward. We report here the synthesis, isolation, and properties of bis(iminodiacetato)oxovanadium(IV) and bis(αα-iminodipropionato)oxovanadium(IV). The complex bis(ββ-iminodipropionato)oxovanadium(IV) has been prepared in solution. These complexes serve as models for Amavadine. The structures of the models are analogous to that of Amavadine, with two bidentate, singly charged ligands bonding through one oxygen and one nitrogen atom. The visible spectra suggest the possibility of 1:1 complexes in solution in addition to the 2:1 ligand to metal complexes. Preliminary electrochemical data suggest reversible V(IV) ? V(III) couples.     

Jasmonic acid prevents the accumulation of cyclin B1;1 and CDK-B in synchronized tobacco BY-2 cells

Jasmonic acid (JA) plays a crucial role in plant fertility and defense responses. It exerts an inhibitory effect on plant growth when applied exogenously. This effect seems to be somehow related to a negative regulation of cell cycle progression in the meristematic tissues. In this report, we focus on the molecular events that occur during JA-induced G2 arrest. We demonstrate that JA prevents the accumulation of B-type cyclin-dependent kinases and the expression of cyclin B1;1, which are both essential for the initiation of mitosis. This feature suggests the existence of an early G2 checkpoint that is affected by JA.     

Oligomeric Hsp33 with enhanced chaperone activity: gel filtration, cross-linking, and small angle x-ray scattering (SAXS) analysis

Hsp33, an Escherichia coli cytosolic chaperone, is inactive under normal conditions but becomes active upon oxidative stress. It was previously shown to dimerize upon activation in a concentration- and temperature-dependent manner. This dimer was thought to bind to aggregation-prone target proteins, preventing their aggregation. In the present study, we report small angle x-ray scattering (SAXS), steady state and time-resolved fluorescence, gel filtration, and glutaraldehyde cross-linking analysis of full-length Hsp33. Our circular dichroism and fluorescence results show that there are significant structural changes in oxidized Hsp33 at different temperatures. SAXS, gel filtration, and glutaraldehyde cross-linking results indicate, in addition to the dimers, the presence of oligomeric species. Oxidation in the presence of physiological salt concentration leads to significant increases in the oligomer population. Our results further show that under conditions that mimic the crowded milieu of the cytosol, oxidized Hsp33 exists predominantly as an oligomeric species. Interestingly, chaperone activity studies show that the oligomeric species is much more efficient compared with the dimers in preventing aggregation of target proteins. Taken together, these results indicate that in the cell, Hsp33 undergoes conformational and quaternary structural changes leading to the formation of oligomeric species in response to oxidative stress. Oligomeric Hsp33 thus might be physiologically relevant under oxidative stress.     

The TORNADO1 and TORNADO2 genes function in several patterning processes during early leaf development in Arabidopsis thaliana

In multicellular organisms, patterning is a process that generates axes in the primary body plan, creates domains upon organ formation, and finally leads to differentiation into tissues and cell types. We identified the Arabidopsis thaliana TORNADO1 (TRN1) and TRN2 genes and their role in leaf patterning processes such as lamina venation, symmetry, and lateral growth. In trn mutants, the leaf venation network had a severely reduced complexity: incomplete loops, no tertiary or quaternary veins, and vascular islands. The leaf laminas were asymmetric and narrow because of a severely reduced cell number. We postulate that the imbalance between cell proliferation and cell differentiation and the altered auxin distribution in both trn mutants cause asymmetric leaf growth and aberrant venation patterning. TRN1 and TRN2 were epistatic to ASYMMETRIC LEAVES1 with respect to leaf asymmetry, consistent with their expression in the shoot apical meristem and leaf primordia. TRN1 codes for a large plant-specific protein with conserved domains also found in a variety of signaling proteins, whereas TRN2 encodes a transmembrane protein of the tetraspanin family whose phylogenetic tree is presented. Double mutant analysis showed that TRN1 and TRN2 act in the same pathway.     

Evaluation of mutation effects on UGT1A1 activity toward 17beta-estradiol using liquid chromatography-tandem mass spectrometry

Mutations in the gene encoding UDP-glucuronosyltransferase 1A1 (UGT1A1) may reduce the glucuronidation of estradiol, bilirubin, etc. In the present study, we used a liquid chromatography-tandem mass spectrometry (LC/MS/MS) method to assay the activities of recombinant mutated UGT1A1 toward 17beta-estradiol (E2), by determining its glucuronide (E2G) content. Direct evidence for glucuronide formation was provided by E2G-specific ion peaks. The UGT1A1 activities of G71R (exon 1), F83L (exon 1), I322V (exon 2) and G493R (exon 5) mutants were 24, 30, 18 and 0.6% of the normal UGT1A1 activity, respectively. In conclusion, our study showed that LC/MS/MS enabled accurate evaluation of the effects of mutations on recombinant UGT1A1 activity towards E2.     

A study on medicinal plants from Malaysia focused on Acalypha siamensis Oliv. ex Gage. isolation and structure of a new tetraterpene, acalyphaser A

As a part of our chemical studies on Malaysian medicinal plants, five Malaysian plant species were evaluated by cytotoxicity assays using P388 murine leukemia cells. Since Acalypha siamensis exhibited the strongest growth inhibition, its constituents were studied as the object of search for bioactive materials. A novel tetraterpene, acalyphaser A (1), was isolated in the course of the purification. Its structure was elucidated on the basis of 1D- and 2D-NMR techniques, and mass spectrometry.