title: A novel small molecular weight GTP-binding protein with the same putative effector domain as the ras proteins in bovine brain membranes. Purification, determination of primary structure, and characterization.
abstract: In the present studies, we have purified a novel small Mr GTP-binding protein, designated as smg p21, to near homogeneity from bovine brain crude membranes, isolated the complementary DNA (cDNA) of this protein from a bovine brain cDNA library, determined the complete nucleotide and deduced amino acid sequences, and characterized the kinetic properties. The cDNA of smg p21 has an open reading frame encoding a protein of 184 amino acids with a calculated Mr of 20,987. The Mr of purified smg p21 is estimated to be about 22,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Homology search indicates that smg p21 is a novel protein with the consensus amino acid sequences for GTP/GDP-binding and GTPase domains but shares about 55% amino acid sequence homology with the human c-Ha-ras protein. Moreover, smg p21 has the same putative effector domain as the Ha-, Ki-, and N-ras proteins at the same position and the same consensus C-terminal sequence as in these ras proteins. Consistent with these structural properties, smg p21 binds specifically [35S] guanosine 5'-(3-O-thio)triphosphate (GTP gamma S), GTP, and GDP with a Kd value for GTP gamma S of about 40 nM. smg p21 binds about 0.7 mol of GTP gamma S/mol of protein. [35S]GTP gamma S-binding to smg p21 is inhibited by pretreatment with N-ethylmaleimide.smg p21 hydrolyzes GTP to liberate Pi with a turnover number of about 0.007 min-1. These kinetic properties of smg p21 are similar to those of the c-ras proteins. These results suggest that smg p21 is a novel GTP-binding protein exerting action(s) similar or antagonistic to that (those) of the ras proteins.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001923:Brain Chemistry; D002417:Cattle; D004247:DNA / Q000032:analysis; D019204:GTP-Binding Proteins / Q000032:analysis* / Q000235:genetics; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D011518:Proto-Oncogene Proteins / Q000032:analysis* / Q000235:genetics; D016283:Proto-Oncogene Proteins p21(ras); D013873:Thionucleotides / Q000378:metabolism
chemical_list: D011518:Proto-Oncogene Proteins; D013873:Thionucleotides; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D004247:DNA; D019204:GTP-Binding Proteins; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)