Wang P, Toyoshima S, Osawa T
Division of Chemical Toxicology and Immunochemistry, Faculty of Pharmaceutical Sciences, University of Tokyo.
J Biochem. 1988 Jan;103(1):137-42. doi: 10.1093/oxfordjournals.jbchem.a122219.
Recently we demonstrated the presence in calf thymocytes of a GTP-binding protein (G-protein) composed of three polypeptides, 54, 41, and 27 kDa, which was physically and functionally associated with a soluble phosphoinositides-specific phospholipase C (PI-phospholipase C). The properties of this G protein were further investigated with the following results. 1) In addition to the ability to bind [35S]guanosine-5'-[gamma-thio]triphosphate (GTP gamma S), the G-protein exhibited GTPase activity, which was enhanced by Mg2+, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol, but inhibited by sodium cholate, GTP gamma S and F-.2) The 54-kDa polypeptide was ADP-ribosylated by pertussis toxin and also by endogenous membrane-bound ADP-ribosyltransferase, but none of these three polypeptides was ADP-ribosylated by cholera toxin. 3) The G-protein did not cross-react with either anti-rat brain alpha 1 (alpha-subunit of inhibitory G-protein, G1), alpha 0 (alpha-subunit of other G1-like G-protein, G0) or beta gamma antibodies. 4) Incubation of this G Protein with GTP gamma S caused dissociation of the three polypeptides. 5) The 27 kDa polypeptide showed GTP-binding activity and enhanced the phosphatidylinositol 4,5-bisphosphate hydrolysis by purified PI-phospholipase C. These results suggest that the PI-phospholipase C-associated G-protein in calf thymocytes may be a novel one and that it is involved in the regulation of PI-phospholipase C activity.
最近我们证明，小牛胸腺细胞中存在一种由54 kDa、41 kDa和27 kDa三种多肽组成的GTP结合蛋白（G蛋白），它在物理和功能上与一种可溶性磷酸肌醇特异性磷脂酶C（PI-磷脂酶C）相关。对这种G蛋白的特性进行了进一步研究，结果如下：1）除了能够结合[35S]鸟苷-5'-[γ-硫代]三磷酸（GTPγS）外，该G蛋白还表现出GTP酶活性，Mg2+、磷脂酰乙醇胺、磷脂酰丝氨酸和磷脂酰肌醇可增强其活性，但胆酸钠、GTPγS和F-可抑制该活性。2）54 kDa的多肽可被百日咳毒素以及内源性膜结合ADP-核糖基转移酶进行ADP-核糖基化，但这三种多肽均未被霍乱毒素进行ADP-核糖基化。3）该G蛋白与抗大鼠脑α1（抑制性G蛋白G1的α亚基）、α0（其他G1样G蛋白G0的α亚基）或βγ抗体均无交叉反应。4）用GTPγS孵育这种G蛋白会导致三种多肽解离。5）27 kDa的多肽表现出GTP结合活性，并增强了纯化的PI-磷脂酶C对磷脂酰肌醇4,5-二磷酸的水解作用。这些结果表明，小牛胸腺细胞中与PI-磷脂酶C相关的G蛋白可能是一种新型G蛋白，并且它参与了PI-磷脂酶C活性的调节。
