title: Molecular model of the G protein alpha subunit based on the crystal structure of the HRAS protein.
abstract: A structural model of guanine nucleotide-binding regulatory protein alpha subunits (G alpha subunits) is proposed based on the crystal structure of the catalytic domain of the human HRAS protein (p21ras). Because of low overall sequence similarity, structural and functional constraints were used to align the G alpha consensus sequence with that of p21ras. The resulting G alpha model specifies the spatial relationship among the guanine nucleotide-binding site, the binding site of the beta gamma subunit complex, likely regions of effector and receptor interaction, and sites of cholera and pertussis toxin modification. The locations in the model of the experimentally determined sites of proteolytic digestion, point mutation, monoclonal antibody binding, and toxin modification are consistent with and help explain the observed biological activity. Two important findings from our model are (i) the orientation of the G alpha model with respect to the membrane and (ii) the identification of the spatial proximity of the N- and C-terminal regions. Furthermore, by analogy to p21ras, the model assigns specific residues in G alpha required for binding the guanosine (G-box) and phosphates (PO4-box) and identifies residues potentially involved in the conformational switch mechanism (S-box). Specification of these critical regions in the G alpha model suggests guidelines for construction of mutants and chimeric proteins to experimentally test structural and functional hypotheses.
authors.affiliation: Division of Chemical Biodynamics, Lawrence Berkeley Laboratory, University of California, Berkeley 94720.
authors.forename: S R
authors.initials: SR
authors.lastname: Holbrook
authors.forename: S H
authors.initials: SH
authors.lastname: Kim
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000595:Amino Acid Sequence; D001665:Binding Sites; D002413:Cations, Divalent; D003460:Crystallization; D019204:GTP-Binding Proteins / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010447:Peptide Hydrolases / Q000378:metabolism; D037342:Pertussis Toxin; D010710:Phosphates / Q000378:metabolism; D011487:Protein Conformation; D011518:Proto-Oncogene Proteins; D016283:Proto-Oncogene Proteins p21(ras); D012689:Sequence Homology, Nucleic Acid; D010566:Virulence Factors, Bordetella / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D002413:Cations, Divalent; D010710:Phosphates; D011518:Proto-Oncogene Proteins; D010566:Virulence Factors, Bordetella; D006153:Guanosine Diphosphate; D000246:Adenosine Diphosphate Ribose; D006160:Guanosine Triphosphate; D037342:Pertussis Toxin; D010447:Peptide Hydrolases; D019204:GTP-Binding Proteins; D016283:Proto-Oncogene Proteins p21(ras)