Structure and functional motifs of GCR1, the only plant protein with a GPCR fold?

Whether GPCRs exist in plants is a fundamental biological question. Interest in deorphanizing new G protein coupled receptors (GPCRs), arises because of their importance in signaling. Within plants, this is controversial as genome analysis has identified 56 putative GPCRs, including GCR1 which is reportedly a remote homologue to class A, B and E GPCRs. Of these, GCR2, is not a GPCR; more recently it has been proposed that none are, not even GCR1. We have addressed this disparity between genome analysis and biological evidence through a structural bioinformatics study, involving fold recognition methods, from which only GCR1 emerges as a strong candidate. To further probe GCR1, we have developed a novel helix alignment method, which has been benchmarked against the the class A – class B - class F GPCR alignments. In addition, we have presented a mutually consistent set of alignments of GCR1 homologues to class A, class B and class F GPCRs, and shown that GCR1 is closer to class A and /or class B GPCRs than class A, class B or class F GPCRs are to each other. To further probe GCR1, we have aligned transmembrane helix 3 of GCR1 to each of the 6 GPCR classes. Variability comparisons provide additional evidence that GCR1 homologues have the GPCR fold. From the alignments and a GCR1 comparative model we have identified motifs that are common to GCR1, class A, B and E GPCRs. We discuss the possibilities that emerge from this controversial evidence that GCR1 has a GPCR fol

The role of ECL2 in CGRP receptor activation: a combined modelling and experimental approach

The calcitonin gene-related peptide (CGRP) receptor is a complex of a calcitonin receptor-like receptor (CLR), which is a family B G-protein-coupled receptor (GPCR) and receptor activity modifying protein 1. The role of the second extracellular loop (ECL2) of CLR in binding CGRP and coupling to Gs was investigated using a combination of mutagenesis and modelling. An alanine scan of residues 271–294 of CLR showed that the ability of CGRP to produce cAMP was impaired by point mutations at 13 residues; most of these also impaired the response to adrenomedullin (AM). These data were used to select probable ECL2-modelled conformations that are involved in agonist binding, allowing the identification of the likely contacts between the peptide and receptor. The implications of the most likely structures for receptor activation are discussed.</jats:p

E-Biothon: an experimental platform for BioInformatics

International audienceThe E-Biothon platform is an experimental Cloud platform to help speed up and advance research in biology, health and environment. It is based on a Blue Gene/P system and a web portal that allow members of the bioinformatics community to easily launch their scientific applications. We describe in this paper the technical capacities of the platform, the different applications supported and finally a set of user experiences on the platform

Computational modelling of G protein-coupled receptors

G protein-coupled receptors (GPCRs) comprise the most "drugable" family of transmembrane proteins, GPCRs share a common structural template and a general mechanism of signal transduction, but vary greatly in sequence conservation, ligand recognition and function. The current set of class A GPCR crystal structures have facilitated the modelling of class A GPCRs. However, other classes of GPCRs have not been so easy to study. The main focus presented in this thesis is the utilisation of class A GPCR structural information to model medically important GPCRs other than class A GPCRs via molecular modelling. The lack of sequence conservation hampers modelling non-class A GPCRs using class A GPCR crystal structures. A plant GPCR, namely GCR1, has sequence homology to more than one GPCR family (class A, Band E GPCRs) and has been used to align the transmembrane region of class A and B GPCRs. Consequently, we have presented a computational protocol for the identification of putative plant GPCRs that may similarly be used to address the difficult issue of alignment between GPCR families but in this respect only GCR1 was found to be useful. GCR1 is still an orphan GPCR with no known cognate ligand. We first assessed whether GCR 1 was a valid GPCR via homology modelling and molecular dynamics. We found that GCR1 has more similarities to class A and class S GPCRs than was previously acknowledged and further support evidence that GCR1 is a GPCR. Consequently, using the class A - GCR1 - class B alignment, we have produced active and inactive homology models of the CGRP receptor, a prototypical class B GPCR. In conjunction with mutation data, these models were used to identify a number of distinct class B motifs and their class A equivalents for the first time. Finally, molecular dynamic simulations were used to further confirm the role of the class B motifs.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Bios2cor: an R package integrating dynamic and evolutionary correlations to identify functionally important residues in proteins

International audienceAbstract Summary Both dynamic correlations in protein sidechain motions during molecular dynamics (MD) simulations and evolutionary correlations in multiple sequence alignments (MSAs) of homologous proteins may reveal functionally important residues. We developed the R package Bios2cor that provides a unique framework to investigate and, possibly, integrate both analyses. Bios2cor starts with an MSA or an MD trajectory and computes correlation/covariation scores between positions in the MSA or between sidechain dihedral angles or rotamers in the MD trajectory. In addition, Bios2cor provides a variety of tools for the analysis, the visualization and the interpretation of the data. Availability and implementation The R package Bios2cor is available from the Comprehensive R Archive Network, at https://CRAN.R-project.org/package=Bios2cor

Deciphering collaborative sidechain motions in proteins during molecular dynamics simulations

International audienceThe dynamic structure of proteins is essential for their functions and may include large conformational transitions which can be studied by molecular dynamics (MD) simulations. However, details of these transitions are difficult to automatically track. To facilitate their analysis, we developed two scores of correlation between sidechain dihedral angles. The CIRCULAR and OMES scores are computed from, respectively, dihedral angle values and rotamer distributions. As a case study, we applied our methods to an activation-like transition of the chemokine receptor CXCR4, observed during accelerated MD simulations. The principal component analysis of the correlation matrices was consistent with the networking structure of the top ranking pairs. Both scores identify a set of residues whose "collaborative" sidechain rotamerization immediately preceded or accompanied the conformational transition of CXCR4. Detailed analysis of the sequential order of these rotamerizations suggests that an allosteric mechanism, involving the outward motion of an asparagine residue in transmembrane helix 3, might be a prerequisite to the large scale conformational transition of CXCR4. This case study provides the proof-of-concept that the correlation methods developed here are valuable exploratory techniques to help decipher complex reactional pathways

Bioinformatics and molecular modelling approaches to GPCR oligomerization

The elusive nature of the structure and function of the G-protein coupled receptor (GPCR) dimer or oligomer has led to a variety of computational studies, most of which have been directed primarily towards understanding structure. Here we review some of the recent studies based on sequence analysis and docking experiments and the recent developments in GPCR structure that have underpinned dimerization studies. In addition, we review recent nanosecond molecular dynamics simulations and coarse-grained methods for investigating the dynamic consequences of dimerization. The strengths and weaknesses of these complementary methods are discussed. The consensus of a variety of studies is that several transmembrane helices are involved in the dimerization/oligomerization interface(s); computation has been particularly effective in elucidating the experiments that seem to indicate a key role for transmembrane helix 4. © 2009 Elsevier Ltd. All rights reserved

Molecular Insights into the Transmembrane Domain of the Thyrotropin Receptor.

The thyrotropin receptor (TSHR) is a G protein-coupled receptor (GPCR) that is member of the leucine-rich repeat subfamily (LGR). In the absence of crystal structure, the success of rational design of ligands targeting the receptor internal cavity depends on the quality of the TSHR models built. In this subfamily, transmembrane helices (TM) 2 and 5 are characterized by the absence of proline compared to most receptors, raising the question of the structural conformation of these helices. To gain insight into the structural properties of these helices, we carried out bioinformatics and experimental studies. Evolutionary analysis of the LGR family revealed a deletion in TM5 but provided no information on TM2. Wild type residues at positions 2.58, 2.59 or 2.60 in TM2 and/or at position 5.50 in TM5 were substituted to proline. Depending on the position of the proline substitution, different effects were observed on membrane expression, glycosylation, constitutive cAMP activity and responses to thyrotropin. Only proline substitution at position 2.59 maintained complex glycosylation and high membrane expression, supporting occurrence of a bulged TM2. The TSHR transmembrane domain was modeled by homology with the orexin 2 receptor, using a protocol that forced the deletion of one residue in the TM5 bulge of the template. The stability of the model was assessed by molecular dynamics simulations. TM5 straightened during the equilibration phase and was stable for the remainder of the simulations. Our data support a structural model of the TSHR transmembrane domain with a bulged TM2 and a straight TM5 that is specific of glycoprotein hormone receptors

Co-Variation Approaches to the Evolution of Protein Families

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Evolution of chemokine receptors is driven by mutations in the sodium binding site.

Chemokines and their receptors (members of the GPCR super-family) are involved in a wide variety of physiological processes and diseases; thus, understanding the specificity of the chemokine receptor family could help develop new receptor specific drugs. Here, we explore the evolutionary mechanisms that led to the emergence of the chemokine receptors. Based on GPCR hierarchical classification, we analyzed nested GPCR sets with an eigen decomposition approach of the sequence covariation matrix and determined three key residues whose mutation was crucial for the emergence of the chemokine receptors and their subsequent divergence into homeostatic and inflammatory receptors. These residues are part of the allosteric sodium binding site. Their structural and functional roles were investigated by molecular dynamics simulations of CXCR4 and CCR5 as prototypes of homeostatic and inflammatory chemokine receptors, respectively. This study indicates that the three mutations crucial for the evolution of the chemokine receptors dramatically altered the sodium binding mode. In CXCR4, the sodium ion is tightly bound by four protein atoms and one water molecule. In CCR5, the sodium ion is mobile within the binding pocket and moves between different sites involving from one to three protein atoms and two to five water molecules. Analysis of chemokine receptor evolution reveals that a highly constrained sodium binding site characterized most ancient receptors, and that the constraints were subsequently loosened during the divergence of this receptor family. We discuss the implications of these findings for the evolution of the chemokine receptor functions and mechanisms of action