Sasaki T, Kikuchi A, Araki S, Hata Y, Isomura M, Kuroda S, Takai Y
Department of Biochemistry, Kobe University School of Medicine, Japan.
J Biol Chem. 1990 Feb 5;265(4):2333-7.
A novel regulatory protein for smg p25A, a ras p21-like GTP-binding protein, was purified to near homogeneity from bovine brain cytosol. This regulatory protein, designated here as smg p25A GDP dissociation inhibitor (GDI), inhibited the dissociation of GDP, but not of guanosine 5'-(3-O-thio)triphosphate (GTPgamma S), from smg p25A. smg p25A GDI also inhibited the binding of GTPgamma S to the GDP-bound form of smg p25A but not of that to the guanine nucleotide-free form. GDI did not stimulate the GTPase activity of smg p25A and by itself showed neither GTPgammaS-binding nor GTPase activity. GDI was inactive for other ras p21/ras p21-like GTP-binding proteins including c-Ha-ras p21, rhoB p20, and smg p21. The Mr value of GDI was estimated to be about 54,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, about 65,000 from the S value (4.5 S), and about 82,000 by gel filtration. The isoelectric point of GDI was about pH 5.6. The activities of GDI were killed by tryptic digestion or heat boiling. These results indicate that bovine brain cytosol contains a regulatory protein for smg p25A that inhibits the dissociation of GDP from and thereby the subsequent binding of GTP to this protein.
一种针对类Ras p21 GTP结合蛋白smg p25A的新型调节蛋白，从牛脑细胞质中纯化至近乎同质。这种调节蛋白，在这里命名为smg p25A GDP解离抑制剂（GDI），抑制了GDP从smg p25A上的解离，但不抑制5'-（3-O-硫代）三磷酸鸟苷（GTPγS）的解离。smg p25A GDI还抑制了GTPγS与smg p25A的GDP结合形式的结合，但不抑制与鸟嘌呤核苷酸游离形式的结合。GDI不刺激smg p25A的GTP酶活性，其本身既不显示GTPγS结合活性也不显示GTP酶活性。GDI对包括c-Ha-ras p21、rhoB p20和smg p21在内的其他Ras p21/类Ras p21 GTP结合蛋白无活性。通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳估计GDI的Mr值约为54,000，根据S值（4.5 S）估计约为65,000，通过凝胶过滤估计约为82,000。GDI的等电点约为pH 5.6。GDI的活性通过胰蛋白酶消化或加热煮沸而丧失。这些结果表明，牛脑细胞质中含有一种针对smg p25A的调节蛋白，该蛋白抑制GDP从该蛋白上的解离，从而抑制随后GTP与该蛋白的结合。
