Covalent inhibition of hAChE by organophosphates causes homodimer dissociation through long-range allosteric effects

Acetylcholinesterase (EC 3.1.1.7), a key acetylcholine-hydrolyzing enzyme in cholinergic neurotransmission, is present in a variety of states in situ, including monomers, C-terminally disulfide-linked homodimers, homotetramers, and up to three tetramers covalently attached to structural subunits. Could oligomerization that ensures high local concentrations of catalytic sites necessary for efficient neurotransmission be affected by environmental factors? Using small-angle X-ray scattering (SAXS) and cryo-EM, we demonstrate that homodimerization of recombinant monomeric human acetylcholinesterase (hAChE) in solution occurs through a C-terminal four-helix bundle at micromolar concentrations. We show that diethylphosphorylation of the active serine in the catalytic gorge or isopropylmethylphosphonylation by the R_P enantiomer of sarin promotes a 10-fold increase in homodimer dissociation. We also demonstrate the dissociation of organophosphate (OP)-conjugated dimers is reversed by structurally diverse oximes 2PAM, HI6, or RS194B, as demonstrated by SAXS of diethylphosphoryl-hAChE. However, binding of oximes to the native ligand-free hAChE, binding of high-affinity reversible ligands, or formation of an S_P-sarin-hAChE conjugate had no effect on homodimerization. Dissociation monitored by time-resolved SAXS occurs in milliseconds, consistent with rates of hAChE covalent inhibition. OP-induced dissociation was not observed in the SAXS profiles of the double-mutant Y337A/F338A, where the active center gorge volume is larger than in wildtype hAChE. These observations suggest a key role of the tightly packed acyl pocket in allosterically triggered OP-induced dimer dissociation, with the potential for local reduction of acetylcholine-hydrolytic power in situ. Computational models predict allosteric correlated motions extending from the acyl pocket toward the four-helix bundle dimerization interface 25 Å away.     

Influences of age and maxillary anterior teeth status on patient's satisfaction with dental appearance and tooth colour

doi: 10.1111/j.1741‐2358.2011.00543.x Influences of age and maxillary anterior teeth status on patient’s satisfaction with dental appearance and tooth colour Objectives: To study the impact of age, gender, tooth colour and maxillary anterior teeth status on patient’s satisfaction with their dental appearance. Material and methods: A total of 259 Caucasian subjects participated in the study (119 men, mean age 56 years; 140 women, mean age 61 years) divided into three age groups (young <35 age; middle aged 35–54 age; old ≥55 age). Their maxillary anterior teeth status was classified into three groups: (1) natural teeth (NTG) group; (2) composite filling group (CFG) and (3) porcelain‐fused‐to‐metal fixed prosthodontic restoration group (FPDG). The participants judged appearance and tooth colour using a scale with three categories: completely dissatisfied, moderately dissatisfied and completely satisfied. Results: Almost half of the participants were completely satisfied with their dental appearance and tooth colour. Half of the ‘young’ and ‘middle‐aged’ participants with natural maxillary anterior teeth were completely satisfied and half of the ‘old’ participants were moderately satisfied with their dental appearance and tooth colour. The majority of participants with composite restorations (45–51%) were moderately satisfied with their dental appearance, one‐third of ‘young’ and ‘middle‐aged’ participants were moderately satisfied or dissatisfied with their tooth colour and more than 70% of older participants were dissatisfied with their tooth colour (p > 0.05). Conclusions: Satisfaction with the appearance of the maxillary anterior teeth differed both between individuals of different age and different dental status.     

Quantitative analysis of troponin I serum values in patients with acute cholecystitis

The diagnosis and staging of acute cholecystitis, upon a lot of diagnostic methods and some scoring systems, is still a great clinical problem. The aim of the study was to investigate if serum Troponin I is elevated in patients with acute cholecystitis. Following informed consent, 65 patients with clinical and laboratory signs of acute cholecystitis were enrolled. All patients had measured serum Troponin I level and an abdominal ultrasound was done before definitive treatment was performed. Increased serum Troponin I level was found in most patients with severe form of acute cholecystitis (p < 0.00001). It reached sensitivity of 94.5% and specificity of 57.1% of this test. In multiple regression analysis Troponin I significantly correlated (p < 0.05) with the serum aspartate aminotransferase (r = 0.27), gamma-glutamyl transferase (r = 0.25) and gallbladder wall (> 6 mm) thickness (r = 0.58). Our study confirms that in most patients with severe and acute cholecystitis, serum Troponin I is increased. Troponin I level is in a lower range than it would be in patients with cardiac muscle damage or necrosis. Measuring serum Troponin I is a fast, reliable and widely performed test that could, with other routinely measured parameters, help in early diagnosis of the severe form of acute cholecystitis.     

In vivo localization at the cellular level of stilbene fluorescence induced by Plasmopara viticola in grapevine leaves

Accurate localization of phytoalexins is a key for better understanding their role. This work aims to localize stilbenes, the main phytoalexins of grapevine. The cellular localization of stilbene fluorescence induced by Plasmopara viticola, the agent of downy mildew, was determined in grapevine leaves of very susceptible, susceptible, and partially resistant genotypes during infection. Laser scanning confocal microscopy and microspectrofluorimetry were used to acquire UV-excited autofluorescence three-dimensional images and spectra of grapevine leaves 5-6 days after inoculation. This noninvasive technique of investigation in vivo was completed with in vitro spectrofluorimetric studies on pure stilbenes as their fluorescence is largely affected by the physicochemical environment in various leaf compartments. Viscosity was the major physicochemical factor influencing stilbene fluorescence intensity, modifying fluorescence yield by more than two orders of magnitude. Striking differences in the localization of stilbene fluorescence induced by P. viticola were observed between the different genotypes. All inoculated genotypes displayed stilbene fluorescence in cell walls of guard cells and periclinal cell walls of epidermal cells. Higher fluorescence intensity was observed in guard-cell walls than in any other compartment due to increased local viscosity. In addition stilbene fluorescence was found in epidermal cell vacuoles of the susceptible genotype and in the infected spongy parenchyma of the partially resistant genotype. The very susceptible genotype was devoid of fluorescence both in the epidermal vacuoles and the mesophyll. This strongly suggests that the resistance of grapevine leaves to P. viticola is correlated with the pattern of localization of induced stilbenes in host tissues.     

Factors affecting distribution pattern of dominant macroinvertebrates in Mantovo Reservoir (Republic of Macedonia)

In the present study, we analysed spatial and temporal heterogeneity of the limnological characteristics to provide more detailed information about the processes taking place within Mantovo Reservoir (Republic of Macedonia). The relationship between principal macroinvertebrate species and environmental variables was analysed in order to explore factors that dominantly affect community distribution pattern. Unlike the most reservoirs, strong longitudinal gradient for suspended organic matter and nutrients (total phosphorous, nitrates and nitrites) along the reservoir doesn??t exist. However, the process of thermal stratification has a strong influence on the metabolism and structure of the Mantovo ecosystem, which can be demonstrated by the vertical and longitudinal distribution of dissolved oxygen (DO), CO₂, pH and metals concentrations. Canonical Correspondence Analysis (CCA) indicated that the main factors controlling spatial distribution of Limnodrilus hoffmeisteri and Chironomus plumosus group were temperature, dissolved oxygen and manganese, including sulphates for C. plumous group. Chaoborus crystallinus showed opposite distribution pattern. Cladotanytarsus mancus group was strongly associated with shallower part (littoral and sublittoral) of Mantovo Reservoir characterized by favourable oxygen condition. None of the environmental variables included in CCA showed any relationship with density of Procladius sp.     

Mapping of the Interaction Site between Sortilin and the p75 Neurotrophin Receptor Reveals a Regulatory Role for the Sortilin Intracellular Domain in p75 Neurotrophin Receptor Shedding and Apoptosis

Neurotrophins comprise a group of neuronal growth factors that are essential for the development and maintenance of the nervous system. However, the immature pro-neurotrophins promote apoptosis by engaging in a complex with sortilin and the p75 neurotrophin receptor (p75^NTR). To identify the interaction site between sortilin and p75^NTR, we analyzed binding between chimeric receptor constructs and truncated p75^NTR variants by co-immunoprecipitation experiments, surface plasmon resonance analysis, and FRET. We found that complex formation between sortilin and p75^NTR relies on contact points in the extracellular domains of the receptors. We also determined that the interaction critically depends on an extracellular juxtamembrane 23-amino acid sequence of p75^NTR. Functional studies further revealed an important regulatory function of the sortilin intracellular domain in p75^NTR-regulated intramembrane proteolysis and apoptosis. Thus, although the intracellular domain of sortilin does not contribute to p75^NTR binding, it does regulate the rates of p75^NTR cleavage, which is required to mediate pro-neurotrophin-stimulated cell death.     

The thermal stability of the external invertase isoforms from Saccharomyces cerevisiae correlates with the surface charge density

Understanding the effect of surface charge on the stability of proteins is one prerequisite for "tailoring" proteins with increased thermal stability. Here, we investigated the origin of the altered thermal stability observed between the four recently isolated isoforms (EINV1-EINV4) of external invertase. External invertase from yeast Saccharomyces cerevisiae, a homodimeric glycoprotein, represents a widely used model for studying the influence of the glyco component on protein stability. The stability of the four isoforms of invertase decreases from EINV1 to EINV4, which is accompanied by an increase in negative surface charge density. Mass spectrometry analysis revealed that the isoforms share identical protein parts indicating that the differences in stability are the result of post-translational modifications. (31)P NMR analysis revealed that the isoforms contain negatively charged phosphate groups in diester and monoester forms attached to the glycan part. The total amount of phosphate bound to the polymannan component varies between the different isoforms. These results, together with the analysis of the amount of polymannan components, show that negative surface charge density does not entirely depend on the amount of phosphate but rather on its distribution. This suggests that charged groups bound to the glyco-component of a protein can influence the stability of glycoproteins.     

Short- and long-term exposure of articular cartilage to curcumin or quercetin inhibits aggrecan loss

The aim of this study was to determine if curcumin and quercetin inhibit induced aggrecan loss from bovine articular cartilage explants given that these polyphenols have been shown to suppress the expression of matrix-degrading enzymes. The kinetics of loss of ³⁵S-aggrecan and the loss of total aggrecan in cartilage explants maintained in catabolic medium containing either 1 μM retinoic acid or 50 ng/ml interleukin (IL)-1α were studied in the presence of either 1–25 μM curcumin or 10–50 μM quercetin. The reversibility of catabolism of ³⁵S-aggrecan was also studied in catabolically stimulated cultures treated with 25 μM curcumin or 50 μM quercetin for the initial 4–5 days of culture followed by 10–15 days of culture in catabolic medium in the absence of either polyphenol. Curcumin and quercetin suppressed ³⁵S-aggrecan and total aggrecan loss from the explants in a dose-dependent manner. When the exposure of explants to curcumin or quercetin was limited to the first 4–5 days of culture, the suppression of ³⁵S-aggrecan loss was maintained in the extended culture period when the tissue was stimulated with either retinoic acid or IL-1α. Quercetin suppressed IL-1α-stimulated expression of a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4. Curcumin suppressed retinoic acid stimulated expression of ADAMTS-5, and both polyphenols suppressed basal expression of ADAMTS-5. The ability of curcumin and quercetin to protect cartilage from stimulated aggrecan loss and to maintain this protection posttreatment may, at least in part, be due to the suppression of gene expression of ADAMTS-4 and -5.     

<Emphasis Type="Italic">In vivo</Emphasis> and <Emphasis Type="Italic">in vitro</Emphasis> antioxidant effects of three Veronica species

The aim of the present study was to examine the antioxidant activity of three Veronica species (Plantaginaceae). The antioxidant potential of various extracts obtained from aerial flowering parts was evaluated by DPPH-free (1,1-diphenyl-2-picrylhydrazyl-free) radical scavenging activity and ferric-reducing antioxidant power assays. Considerable antioxidant activity was observed in the plant samples (FRAP values ranged from 0.97 to 4.85 mmol Fe²⁺/g, and DPPH IC₅₀ values from 12.58 to 66.34 μg/ml); however, these levels were lower than the activity of the control compound butylated hydroxytoluene (BHT) (FRAP: 10.58 mmol Fe²⁺/g; DPPH IC₅₀: 9.57 μg/ml). Also, the in vivo antioxidant effects were evaluated in several hepatic antioxidant systems in rats (activities of glutathione peroxidase, glutathione reductase, peroxidase, catalase, xanthine oxidase, glutathione content and level of thiobarbituric acid reactive substances) after treatment with different Veronica extracts, or in combination with carbon tetrachloride (CCl₄). Pretreatment with 100 mg/kg b.w. of Veronica extracts inhibited CCl₄-induced liver injury by decreasing TBA-RS level, increasing GSH content, and bringing the activities of CAT and Px to control levels. The present study suggests that the extracts analyzed could protect the liver cells from CCl₄-induced liver damage by their antioxidative effect on hepatocytes.     

Intrinsic disorder in putative protein sequences

Background

Intrinsically disordered proteins (IDPs) and regions (IDRs) perform a variety of crucial biological functions despite lacking stable tertiary structure under physiological conditions in vitro. State-of-the-art sequence-based predictors of intrinsic disorder are achieving per-residue accuracies over 80%. In a genome-wide study of intrinsic disorder in human genome we observed a big difference in predicted disorder content between confirmed and putative human proteins. We investigated a hypothesis that this discrepancy is not correct, and that it is due to incorrectly annotated parts of the putative protein sequences that exhibit some similarities to confirmed IDRs, which lead to high predicted disorder content.

Methods

To test this hypothesis we trained a predictor to discriminate sequences of real proteins from synthetic sequences that mimic errors of gene finding algorithms. We developed a procedure to create synthetic peptide sequences by translation of non-coding regions of genomic sequences and translation of coding regions with incorrect codon alignment.

Results

Application of the developed predictor to putative human protein sequences showed that they contain a substantial fraction of incorrectly assigned regions. These regions are predicted to have higher levels of disorder content than correctly assigned regions. This partially, albeit not completely, explains the observed discrepancy in predicted disorder content between confirmed and putative human proteins.

Conclusions

Our findings provide the first evidence that current practice of predicting disorder content in putative sequences should be reconsidered, as such estimates may be biased.