Wilcox M D, Dingus J, Balcueva E A, McIntire W E, Mehta N D, Schey K L, Robishaw J D, Hildebrandt J D
Department of Pharmacology, Medical University of South Carolina, Charleston 29464.
J Biol Chem. 1995 Mar 3;270(9):4189-92. doi: 10.1074/jbc.270.9.4189.
The gamma subunit composition of the major bovine brain Go and Gi proteins (GOA, GOB, GOC, Gi1, and Gi2) was characterized using antibodies against specific gamma isoforms. Each of the purified G protein heterotrimers contained a heterogeneous population of gamma subunits, and the profiles of the gamma subunits found with Gi1, Gi2, and GOA were similar. In contrast, each GO isoform had a distinct pattern of associated gamma subunits. These differences were surprising given that all three alpha O isoforms are thought to share a common amino-terminal sequence important for the binding of beta gamma dimers and that the alpha OA and alpha OC proteins may come from the same alpha O1 mRNA. The free alpha OA and alpha OC subunits had unique elution behaviors during MonoQ chromatography, compatible with differences in their post-translational processing. These results indicate that both the alpha and gamma subunit compositions of heterotrimers define the structure of an intact G protein. Furthermore, the exact subunit composition of G protein heterotrimers may depend upon regulated expression of different subunit isoforms or upon cellular processing of alpha subunits.
利用针对特定γ亚型的抗体对主要牛脑Go和Gi蛋白（GOA、GOB、GOC、Gi1和Gi2）的γ亚基组成进行了表征。每种纯化的G蛋白异源三聚体都包含γ亚基的异质群体，并且在Gi1、Gi2和GOA中发现的γ亚基谱相似。相比之下，每种GO亚型都有独特的相关γ亚基模式。鉴于所有三种αO亚型被认为共享一个对βγ二聚体结合很重要的共同氨基末端序列，并且αOA和αOC蛋白可能来自相同的αO1 mRNA，这些差异令人惊讶。游离的αOA和αOC亚基在MonoQ色谱过程中具有独特的洗脱行为，这与它们翻译后加工的差异相符。这些结果表明，异源三聚体的α和γ亚基组成都决定了完整G蛋白的结构。此外，G蛋白异源三聚体的确切亚基组成可能取决于不同亚基亚型的调控表达或α亚基的细胞加工。
