Rahmatullah M, Ginnan R, Robishaw J D
Weis Center for Research, Geisinger Clinic, Danville, Pennsylvania 17822.
J Biol Chem. 1995 Feb 17;270(7):2946-51. doi: 10.1074/jbc.270.7.2946.
The existence of multiple alpha, beta, and gamma subunits raises questions regarding the assembly of particular G proteins. Based on the results of a previous study (Rahmatullah, M., and Robishaw, J. D. (1994) J. Biol. Chem. 269, 3574-3580), we hypothesized that the assembly of G proteins may be determined by the interactions of the more structurally diverse alpha and gamma subunits. This hypothesis was confirmed in the present study by showing striking differences in the abilities of the gamma 1 and gamma 2 subunits to interact with the alpha o subunit. Chimeras of the gamma 1 and gamma 2 subunits were used to delineate which region is responsible. Support for the importance of the N-terminal region of the gamma subunit comes from our observations that 1) the gamma 2 subunit and the gamma 211 chimera bound strongly to the alpha o-agarose matrix, but the gamma 1 subunit and the gamma 112 chimera bound weakly, if at all; 2) an N-terminal peptide made to the gamma 2 subunit blocked the binding of the gamma 211 chimera to the alpha o-agarose matrix; 3) both the gamma 211 chimera and the N-terminal peptide were able to partially protect the alpha o subunit against tryptic cleavage; and 4) the gamma 211 chimera, but not the gamma 112 chimera, supported ADP-ribosylation of the alpha o subunit.
多种α、β和γ亚基的存在引发了关于特定G蛋白组装的问题。基于先前一项研究的结果（拉赫马图拉，M.，和罗比肖，J. D.（1994年）《生物化学杂志》269卷，3574 - 3580页），我们推测G蛋白的组装可能由结构上更多样化的α和γ亚基之间的相互作用决定。在本研究中，通过显示γ1和γ2亚基与αo亚基相互作用能力的显著差异，证实了这一推测。使用γ1和γ2亚基的嵌合体来确定哪个区域起作用。对γ亚基N端区域重要性的支持来自我们的观察结果：（1）γ2亚基和γ211嵌合体与αo - 琼脂糖基质强烈结合，但γ1亚基和γ112嵌合体即使结合也很弱；（2）针对γ2亚基制备的N端肽阻断了γ211嵌合体与αo - 琼脂糖基质的结合；（3）γ211嵌合体和N端肽都能够部分保护αo亚基免受胰蛋白酶切割；（4）γ211嵌合体而非γ112嵌合体支持αo亚基的ADP - 核糖基化。
