Coupling of agonist binding to effector domain activation in metabotropic glutamate-like receptors

Many membrane receptors are made of a ligand binding domain and an effector domain mediating intracellular signaling. This is the case for the metabotropic glutamate-like G-protein-coupled receptors. How ligand binding leads to the active conformation of the effector domain in such receptors is largely unknown. Here, we used an evolutionary trace analysis and mutagenesis to identify critical residues involved in the allosteric coupling between the Venus flytrap ligand binding domain (VFT) and the heptahelical G-protein activating domain of the metabotropic glutamate-like receptors. We have shown that a conserved interdomain disulfide bridge is required for this allosteric interaction. Taking into account that these receptors are homodimers, this finding provides important new information explaining how the different conformations of the dimer of VFT lead to different signaling of such dimeric receptors.     

Isozyme differentiation of aldolase and pyruvate kinase in fetal,regenerating, preneoplastic,and malignant rat hepatocytes during culture

Summary Aldolase and pyruvate kinase isozymes were investigated in cultured hepatocytes from fetal, regenerating, and 2-acetyl-aminofluorene-fed rat liver as well as in some epithelial liver cell lines. Our results show that: (a) cell proliferation and prolonged expression of specific isozymes were found only in cultured hepatocytes from 17-day old fetuses; (b) the fetal type of pyruvate kinase expressed in regenerating and carcinogen-treated liver was temporarily lost only in cultured hepatocytes from regenerating liver; (c) the adult type of aldolase and pyruvate kinase was absent in one epithelial cell line derived from a carcinogen-treated liver and in the hepatoma tissue cell (HTC) line but was found in the Faza clone of the Reuber H₃₅ cell line during the 50 first passages in vitro; and (d) the isozyme pattern of pyruvate kinase was always more strongly shifted than that of aldolase. The observations suggest that: (a) hepatocytes from carcinogen-treated liver exhibit the same lack of ability to proliferate in primary culture as normal adult hepatocytes; (b) adult hepatocytes can produce fetal isozymes without prior cell division; (c) pyruvate kinase is a stronger marker of dedifferentiation (retrodifferentiation) than aldolase; and (d) regulatory processes of isozyme expression are different during ontogenesis, regeneration, and hepatocarcinogenesis. This work was supported by the “Institut National de la Santé et de la Recherche Médicale” and the “Fondation pour la Recherche Medicale Fran?aise”     

Verbal cues modulate hedonic perception of odors in 5-year-old children as well as in adults

The judgment of pleasantness/unpleasantness is the prominent reaction to the olfactory world. In human adults, the hedonic valence of odor perception is affected by various factors, among which is an individual's lexical knowledge about smells. The present study examined whether such top-down effects of lexical knowledge on hedonic judgment of olfactory input are similar in children (5-6 years) and adults (20-25 years). In both groups, the lexical knowledge was found to influence the perception of the least emotional (or most neutral) odors: the pleasantness of the smells of banana and mint was enhanced when participants were given the corresponding odor label before olfactory sensation. These results lend support to the notion that, during childhood, smells are not only encoded perceptually but that verbal encoding also steers contextual effects that may be prominent factors in the early memorization and categorization of odors.     

Conspicuous endolithic algal associations in a mesophotic reef-building coral

Coral Reefs - Understanding how corals and their symbionts specialize across depth gradients allows us to understand biodiversity in shallow and mesophotic coral ecosystems. Here we determined the...     

Biochemical comparison of two proteolytic enzymes from Carica candamarcensis: Structural motifs underlying resistance to cystatin inhibition

The lattices of Carica candamarcensis and Carica papaya, members of the Caricaceae family, contain isoforms of cysteine proteinases that help protect these plants against injury. In a prior study, we fractionated 14 discrete proteinaceous components from C. candamarcensis, two of them displaying mitogenic activity in mammalian cells. In this study, we compared the kinetic parameters of one of the mitogenic proteinases (CMS2MS2) with one of the isoforms displaying the highest enzyme activity of this group (CMS1MS2). Both enzymes display a similar Km value with either BAPNA (Benzoyl-Arg-pNA) or PFLPNA (Pyr-Phe-Leu-pNA), but the kcat of CMS1MS2 is about 14-fold higher for BAPNA and 129-fold higher with PFLPNA. While both enzymes are inhibited by E-64 and iodoacetamide, chicken cystatin fully inhibits CMS1MS2, but scarcely affects activity of CMS2MS2. Based on the structure of these proteins and other enzymes from the Caricaceae family whose structures have been resolved, it is proposed that Arg¹⁸⁰ located in the cleft at the active site in CMS2MS2 is responsible for its resistance to cystatin.     

How important are Rho GTPases in neurosecretion?

Rho GTPases are small GTP binding proteins belonging to the Ras superfamily which act as molecular switches that regulate many cellular function including cell morphology, cell to cell interaction, cell migration and adhesion. In neuronal cells, Rho GTPases have been proposed to regulate neuronal development and synaptic plasticity. However, the role of Rho GTPases in neurosecretion is poorly documented. In this review, we discuss data that highlight the importance of Rho GTPases and their regulators into the control of neurotransmitter and hormone release in neurons and neuroendocrine cells, respectively.     

Rotavirus VP4 and VP7-Derived Synthetic Peptides as Potential Substrates of Protein Disulfide Isomerase Lead to Inhibition of Rotavirus Infection

Rotavirus infection of MA104 cells has been shown to be inhibited by cell membrane-impermeant thiol/disulfide exchange inhibitors and anti-PDI antibodies. To characterise the amino acid sequences of rotavirus structural proteins potentially mediating cell surface PDI?Csubstrate interactions, rotavirus-derived peptides from VP4 and VP7 (RRV) and VP7 (Wa), and their modified versions containing serine instead of cysteine were synthesized. Cysteine-containing VP7 peptides corresponding to residues 189?C210 or 243?C263 caused an infectivity inhibitory effect of about 64 and 85?%, respectively, when added to cells. Changing cysteine to serine significantly decreased the inhibitory effect. A cysteine-containing peptide corresponding to VP4 residues 200?C219 and its scrambled version reduced infectivity by 92 and 80?%, respectively. A cysteine to serine change in the original VP4 200?C219 peptide did not affect its inhibitory effect. Non-rotavirus related sequences containing cysteine residues efficiently inhibited rotavirus infectivity. Antibodies against VP7 residues 189?C210 or 243?C263 significantly inhibited rotavirus infectivity only after virus attachment to cells had occurred, whereas those against VP4 200?C219 peptide inhibited infectivity irrespective of whether virus or cell-attached virus was antibody-treated. A direct PDI?Cpeptide interaction was shown by ELISA for cysteine-containing VP7 and VP4 peptides. Virus?Ccell attachment was unaffected by the peptides inhibiting virus infectivity. The results showed that even though cysteine residues in the peptides tested are important in both virus infectivity inhibition and in vitro PDI?Cpeptide interaction, the accompanying amino acid sequence also plays some role. As a whole, our findings further support our hypothesis that cell surface PDI from MA104 cells might be contributing to rotavirus entry at a post-attachment step.     

Benthic indicators of sediment quality associated with run-of-river reservoirs

Freshwater ecosystems have been fragmented by the construction of large numbers of dams. In addition to disruption of ecological continuity and physical disturbance downstream, accumulation of large amounts of sediment within run-of-river reservoirs constitutes a latent ecotoxic risk to aquatic communities. To date, run-of-river reservoirs and ecotoxic risks associated with contaminated sediment to the biodiversity and functioning of such systems are little studied. Therefore, the main objective of this study was to describe macroinvertebrate assemblages, and the functioning of these systems, and to propose indicators of sediment contamination to integrate in in-situ risk assessment methodology. To identify specific assemblages of run-of-river reservoirs, we first compared macroinvertebrate assemblages and their biotrait profiles (i.e. from a database of biological and ecological traits) in reservoirs (n = 6) and associated river sites (upstream and downstream of dams). Then, we compared responses of assemblages and biotrait profiles to sediment contamination of the banks and channels of reservoirs to select the most useful spatial scale to identify sediment contamination. Nineteen indicator taxa were observed to be specifically associated with channel habitats of reservoirs. Among these, the abundance of three taxa (Tanypodinae (Diptera), Ephemerella (Ephemeroptera) and Atherix (Diptera)) revealed the effect of metal sediment contamination. “Between-reservoirs” differences in their biotrait profile were found along the contamination gradient, with a shift of communities’ composition and functionality, and an increase in functional similarity. Many traits (response traits), for example “maximum size”, “transverse distribution”, “substrate preferences”, “saprobity”, “temperature”, “resistance forms”, and “locomotion”, were specifically linked to contamination of sediments by metals. This study indicates how sediment contamination can change the structural and functional composition of run-of-river reservoir assemblages. Indicator taxa and response traits identified in this study could improve current risk assessment methodology and potentially enable prediction of the risks of contaminated sediments stored in reservoirs in downstream ecosystems.