title: Structural Determinants of Constitutive Activation of Gα Proteins: Transducin as a Paradigm.
abstract: Heterotrimeric guanine nucleotide-binding proteins (Gα proteins) are intracellular nanomachines deputed to signal transduction. The switch-on process requires the release of bound GDP from a site at the interface between GTPase and helical domains. Nucleotide release is catalyzed by G protein Coupled Receptors (GPCRs). Here we investigate the functional dynamics of wild type (WT) and six constitutively active mutants (CAMs) of the Gα protein transducin (Gt) by combining atomistic molecular dynamics (MD) simulations with Maxwell-Demod discrete MD (MDdMD) simulations of the receptor-catalyzed transition between GDP-bound and nucleotide-free states. Compared to the WT, Gt CAMs increase the overall fluctuations of nucleotide and its binding site. This is accompanied by weakening of native links involving GDP, α1, the G boxes, β1-β3, and α5. Collectively, constitutive activation by the considered mutants seems to associate with weakening of the interfaces between α5 and the surrounding portions and the interface between GTPase (G) and helical (H) domains. These mutational effects associate with increases in the overall fluctuations of the G and H domains, which reflect on the collective motions of the protein. Gt CAMs, with prominence to G56P, T325A, and F332A, prioritize collective motions of the H domain overlapping with the collective motions associated with receptor-catalyzed nucleotide release. In spite of different local perturbations, the mechanisms of nucleotide exchange catalyzed by activating mutations and by receptor are expected to employ similar molecular switches in the nucleotide binding site and to share the detachment of the H domain from the G domain.
authors.affiliation: Department of Life Sciences, University of Modena and Reggio Emilia , via Campi 103, 41125 Modena, Italy.
authors.forename: Angelo
authors.initials: A
authors.lastname: Felline
authors.affiliation: Department of Life Sciences, University of Modena and Reggio Emilia , via Campi 103, 41125 Modena, Italy.
authors.forename: Simona
authors.initials: S
authors.lastname: Mariani
authors.affiliation: Department of Life Sciences, University of Modena and Reggio Emilia , via Campi 103, 41125 Modena, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Raimondi
authors.affiliation: Department of Life Sciences, University of Modena and Reggio Emilia , via Campi 103, 41125 Modena, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Bellucci
authors.affiliation: Department of Life Sciences, University of Modena and Reggio Emilia , via Campi 103, 41125 Modena, Italy.
authors.forename: Francesca
authors.identifier: http://orcid.org/0000-0002-7620-6895
authors.initials: F
authors.lastname: Fanelli
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D044385:GTP-Binding Protein alpha Subunits / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D056004:Molecular Dynamics Simulation; D009154:Mutation; D009711:Nucleotides / Q000378:metabolism; D000072417:Protein Domains; D015293:Transducin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D044385:GTP-Binding Protein alpha Subunits; D009711:Nucleotides; D015293:Transducin