The main excitatory neurotransmitter in the brain, glutamate (Glu), activates not only receptor-channels, but also receptors coupled to G-protein called metabotropic Glu receptors (mGluRs). Eight ...genes coding for mGluRs have been characterized to date giving rise to even more proteins due to alternative splicing phenomena. Here we characterized a splice variant of mGluR5, called mGluR5b which contains a 32 amino acid fragment inserted in the cytoplasmic tail, 50 residues after the 7th transmembrane domain. mGluR5b mRNAs are present in different regions of the adult rat brain and are expressed at a higher level than mGluR5a mRNA. Functional analysis of mGluR5a and mGluR5b revealed that they share all the properties of mGluR1a, but not those of mGluR1b or 1c. Like mGluR1a, both mGluR5a and mGluR5b activate a rapid and transient current in Xenopus oocytes. When expressed in LLC-PK1 cells, they show the same subcellular distribution as mGluR1a, and stimulate both inositol phosphate (IP) and cAMP production. Moreover, cells expressing mGluR5a or mGluR5b, like those expressing mGluR1a have a higher basal PLC activity that is not inhibited by glutamate-pyruvate transaminase (GPT), suggesting that these receptors have an intrinsic activity. Interestingly, the pharmacological profiles of mGluR5a and b are identical, but different from that of mGluR1a. Most agonists, except glutamate, are more potent on mGluR5a/b than on mGluR1a. Interestingly, the mGluR1a antagonists MCPG and 4CPG have no effect on mGluR5a/b; 4C3HPG which is a full antagonist at mGluR1a is a partial agonist at mGluR5a/b. These results indicate that the long C-terminal intracellular domain present only in mGluR1a and mGluR5a/b, although not well conserved, is likely to be involved in the specific functional properties of these receptors. Although the ligand recognition sites of mGluR5a/b and mGluR1a are highly conserved, these receptors have different pharmacology.
Distribution of trace elements and porosity in soil horizons at the aggregate scale Cornu Sophie, Unite de science du sol, (France). Avenue de la pomme de pin. INRA Orleans; Cousin Isabelle, Unite de science du sol, (France). Avenue de la pomme de pin. INRA Orleans; Deschatrettes Valerie, Unite de science du sol, (France). Avenue de la pomme de pin. INRA Orleans ...
2002
Conference Proceeding
Conjugate microstructural and hydrodynamic evolution of a soil crust during its formation Cousin Isabelle, Unite de Science du Sol, (France). Avenue de la Pomme de Pin; Malam Issa Oumarou, Unite de Science du Sol, (France). Avenue de la Pomme de Pin; Le Bissonnais Yves, Unite de Science du Sol, (France). Avenue de la Pomme de Pin
2002
Conference Proceeding
Dans les années 2000, des agriculteurs désireux de cultiver des blés correspondant à leurs besoins et soucieux d’affirmer leur autonomie vis-à-vis de l’industrie semencière, ont entrepris de relancer ...la sélection paysanne à la ferme. Des collaborations ont été tissées avec des généticiens de l’Inra, et se sont progressivement développées dans le cadre de projets financés. Or les financements de recherche impliquent une formalisation des partenariats, des engagements en termes de résultats académiques et une augmentation significative de la taille des projets. Dans ce nouveau contexte, comment préserver les valeurs d’émancipation paysanne et de justice cognitive sur lesquelles la collaboration paysans-chercheurs s’est originellement construite ? Cet article aborde la façon dont ce défi se pose concrètement aux acteurs de ces projets, et les précautions qu’ils mettent en œuvre pour y faire face.
Heptahelical receptor coupling selectivity to G-proteins is controlled by a large contact area that involves several portions of the receptor and each subunit of the G-protein. In the G-protein α ...subunit, the C-terminal 5 residues, the N terminus, and the αN-β1 and α4–α5 loops play important roles. On the receptor side, both the second and third (i2 and i3) intracellular loops as well as the C-terminal tail probably contact these different regions of the G-protein. It is now accepted that the C terminus of the α subunit binds in a cavity formed by the i2 and i3 loops. Among the various G-protein-coupled receptors (GPCRs), class III receptors that include metabotropic glutamate (mGlu) receptors greatly differ from the rhodopsin-like GPCRs, but the contact zone between these receptors and the G-protein is less understood. The C terminus of the α subunit has been shown to play a pivotal role in the selective recognition of class III GPCRs. Indeed, the mGlu2 and mGlu4 and -8 receptors can discriminate between α subunits that differ at the level of their C-terminal end only (such as Gqo and Gqz). Here, we examine the role of the i2 loop of mGluRs in the selective recognition of this region of the α subunit. To that aim, we analyzed the coupling properties of mGlu2 and mGlu4 or -8 receptors and chimeras containing the i2 loop of the converse receptor to G-protein α subunits that only differ by their C termini (Gqo,Gqz, and their point mutants). Our data demonstrate that the central portion of the i2 loop is responsible for the selective recognition of the C-terminal end of the α subunit, especially the residue on position –4. These data are consistent with the proposal that the C-terminal end of the G-protein α subunit interacts with residues in a cavity formed by the i2 and i3 loops in class III GPCRs, as reported for class I GPCRs.
A Symposium on Nutrition and Cognition: Towards Research and Application for Different Life Stages was held on October 2010 in Malaysia. The influence of diet and nutrition on the cognitive ...development of the child and on cognitive decline in later life was reviewed. Central to the study of such topics is the assessment of cognitive functioning. Cognitive functioning falls into six main areas: executive functioning, memory, attention, perception, psychomotor and language skills, although each domain can be further subdivided. As it is in the nature of human functioning that the performance on any cognitive test can reflect aspects of many of these domains, ideally a battery of tests should be used to establish the basis of any difference in performance. In intervention studies, frequently there has been a failure to demonstrate a beneficial influence of changes in diet. A possible reason is that studies have failed to acknowledge the time scale and critical ages over which diet has an impact. Diet may have a slow and progressive influence making it difficult for short-term studies to show an improvement. In addition, as many factors influence human behaviour, dietary interventions should only be one part of a coordinated approach; the effect of diet will depend on the social and psychological context in which an individual lives. Placing diet into a broader social and psychological context greatly increases the chance of generating significant findings. This report highlights and reviews presentations and discussions at the symposium.
To investigate the structural requirements for selective activation or blockade of metabotropic glutamate receptors, we developed a pharmacophore model for group I (mGluR1) and group II (mGluR2) ...agonists. The Apex-3D program was used with a training set of known active, inactive, and/or selective compounds with a wide structural diversity. The pharmacophore models were then validated by testing a set of additional known agonists. We also used competitive antagonist superpositions in order to define more precisely the topology of the mGluR1 and mGluR2 agonists' recognition site. Both models account for the activity of most potent compounds and show that the selectivity between mGluR1 and mGluR2 subtypes may be due to excluded volumes and additional binding sites, while the relative spatial position of functional groups (NH2, α- and γ-CO2H) remains very similar. On both models glutamate lies in an extended form. An additional binding site is disclosed on mGluR1, while this region would be forbidden on mGluR2. This new site combines a closed and an open model for mGluR1 and accounts for the increased affinity of quisqualic acid. The models show another large hydrophobic region which is tolerated for mGluR2 and restricted for mGluR1.
The prolactin receptor (PRLR) is emerging as a therapeutic target in oncology. Knowledge-based drug design led to the development of a pure PRLR antagonist (Del1-9-G129R-hPRL) that was recently shown ...to prevent PRL-induced mouse prostate tumorogenesis. In humans, the first gain-of-function mutation of the PRLR (PRLR(I146L)) was recently identified in breast tumor patients. At the molecular level, the actual mechanism of action of these two novel players in the PRL system remains elusive. In this study, we addressed whether constitutive PRLR activation (PRLR(I146L)) or PRLR blockade (antagonist) involved alteration of receptor oligomerization and/or of inter-chain distances compared to unstimulated and PRL-stimulated PRLR. Using a combination of various biochemical and spectroscopic approaches (co-IP, blue native electrophoresis, BRET(1)), we demonstrated that preformed PRLR homodimers are altered neither by PRL- or I146L-induced receptor triggering, nor by antagonist-mediated blockade. These findings were confirmed using a novel time-resolved fluorescence resonance energy transfer (TR-FRET) technology that allows monitoring distance changes between cell surface tagged receptors. This technology revealed that PRLR blockade or activation did not involve detectable distance changes between extracellular domains of receptor chains within the dimer. This study merges with our previous structural investigations suggesting that the mechanism of PRLR activation solely involves intermolecular contact adaptations leading to subtle intramolecular rearrangements.
The gamma-aminobutyric acid (GABA) receptor type B (GABA(B)R) is constituted of at least two homologous proteins, GABA(B)R1 and GABA(B)R2. These proteins share sequence and structural similarity with ...metabotropic glutamate and Ca(2+)-sensing receptors, both of which are sensitive to Ca(2+). Using rat brain membranes, we report here that the affinity of GABA and 3-aminopropylphosphinic acid for the GABA(B)R receptor is decreased by a factor >10 in the absence of Ca(2+). Such a large effect of Ca(2+) is not observed with baclofen or the antagonists CGP64213 and CGP56999A. In contrast to baclofen, the potency of GABA in stimulating GTPgammaS binding in rat brain membranes is also decreased by a factor >10 upon Ca(2+) removal. The potency for Ca(2+) in regulating GABA affinity was 37 microM. In cells expressing GABA(B)R1, the potency of GABA, but not of baclofen, in displacing bound (125)I-CGP64213 was similarly decreased in the absence of Ca(2+). To identify residues that are responsible for the Ca(2+) effect, the pharmacological profile and the Ca(2+) sensitivity of a series of GABA(B)R1 mutants were examined. The mutation of Ser269 into Ala was found to decrease the affinity of GABA, but not of baclofen, and the GABA affinity was found not to be affected upon Ca(2+) removal. Finally, the effect of Ca(2+) on the GABA(B) receptor function is no longer observed in cells coexpressing this GABA(B)R1-S269A mutant and the wild-type GABA(B)R2. Taken together, these results show that Ser269, which is conserved in the GABA(B)R1 protein from Caenorhabditis elegans to mammals, is critical for the Ca(2+)-effect on the heteromeric GABA(B) receptor.
Specific domains of the G-protein α subunit have been shown to control coupling to heptahelical receptors. The extreme N and C termini and a region between α4 and α5 helices of the G-protein α ...subunit are known to determine selective interaction with the receptors. The metabotropic glutamate receptor 2 activated both mouse Gα15 and its human homologue Gα16, whereas metabotropic glutamate receptor 8 activated Gα15 only. The extreme C-terminal 20 amino acid residues are identical between the Gα15 and Gα16 and are therefore unlikely to be involved in coupling selectivity. Our data reveal two regions on Gα16 that inhibit its coupling to metabotropic glutamate receptor 8. On a three-dimensional model, both regions are found in a close proximity to the extreme C terminus of Gα16. One module comprises α4 helix, α4−β6 loop (L9 Loop), β6 sheet, and α5 helix. The other, not described previously, is located within the loop that links the N-terminal α helix to the β1 strand of the Ras-like domain of the α subunit. Coupling of Gα16 protein to the metabotropic glutamate receptor 8 is partially modulated by each module alone, whereas both modules are needed to eliminate the coupling fully.
PDF
