title: Mechanism of the intrinsic arginine finger in heterotrimeric G proteins.
abstract: Heterotrimeric G proteins are crucial molecular switches that maintain a large number of physiological processes in cells. The signal is encoded into surface alterations of the Gα subunit that carries GTP in its active state and GDP in its inactive state. The ability of the Gα subunit to hydrolyze GTP is essential for signal termination. Regulator of G protein signaling (RGS) proteins accelerates this process. A key player in this catalyzed reaction is an arginine residue, Arg178 in Gαi1, which is already an intrinsic part of the catalytic center in Gα in contrast to small GTPases, at which the corresponding GTPase-activating protein (GAP) provides the arginine "finger." We applied time-resolved FTIR spectroscopy in combination with isotopic labeling and site-directed mutagenesis to reveal the molecular mechanism, especially of the role of Arg178 in the intrinsic Gαi1mechanism and the RGS4-catalyzed mechanism. Complementary biomolecular simulations (molecular mechanics with molecular dynamics and coupled quantum mechanics/molecular mechanics) were performed. Our findings show that Arg178 is bound to γ-GTP for the intrinsic Gαi1mechanism and pushed toward a bidentate α-γ-GTP coordination for the Gαi1·RGS4 mechanism. This movement induces a charge shift toward β-GTP, increases the planarity of γ-GTP, and thereby catalyzes the hydrolysis.
authors.affiliation: Department of Biophysics, Ruhr University Bochum, 44780 Bochum, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Mann
authors.affiliation: Department of Biophysics, Ruhr University Bochum, 44780 Bochum, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Teuber
authors.affiliation: Department of Biophysics, Ruhr University Bochum, 44780 Bochum, Germany.
authors.forename: Stefan A
authors.initials: SA
authors.lastname: Tennigkeit
authors.affiliation: Department of Biophysics, Ruhr University Bochum, 44780 Bochum, Germany.
authors.forename: Grit
authors.initials: G
authors.lastname: Schröter
authors.affiliation: Department of Biophysics, Ruhr University Bochum, 44780 Bochum, Germany; carsten.koetting@rub.de gerwert@bph.rub.de.|Partner Institute for Computational Biology, 200031 Shanghai, China.
authors.forename: Klaus
authors.initials: K
authors.lastname: Gerwert
authors.affiliation: Department of Biophysics, Ruhr University Bochum, 44780 Bochum, Germany; carsten.koetting@rub.de gerwert@bph.rub.de.
authors.forename: Carsten
authors.identifier: 0000-0002-3599-9657
authors.initials: C
authors.lastname: Kötting
mesh_terms: D001120:Arginine / Q000737:chemistry; D020134:Catalytic Domain; D004795:Enzyme Stability; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D020962:Heterotrimeric GTP-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D016297:Mutagenesis, Site-Directed; D025542:Neurofibromin 1 / Q000737:chemistry / Q000378:metabolism; D020710:RGS Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D025542:Neurofibromin 1; D020710:RGS Proteins; D011994:Recombinant Proteins; C098799:RGS4 protein; D006160:Guanosine Triphosphate; D001120:Arginine; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D020962:Heterotrimeric GTP-Binding Proteins
keywords: FTIR spectroscopy; GTPase; QM/MM calculations; arginine finger; reaction mechanism