Maltese W A, Robishaw J D
Weis Center for Research, Geisinger Clinic, Danville, Pennsylvania 17822.
J Biol Chem. 1990 Oct 25;265(30):18071-4.
The predicted amino acid sequences for the Gi alpha 1 and G gamma 6 subunits of brain heterotrimeric G-proteins both contain C-terminal Cys-A-A-X elements (A is an aliphatic residue and X is any amino acid). This domain represents the site of Cys thioether modification by isoprenoids in p21ras, nuclear lamins, and fungal mating factors. We now show that G gamma 6, translated in reticulocyte lysate, is efficiently labeled with the isoprenoid precursor, [3H]mevalonate. Alteration of the sequence of G gamma 6 so that a Gly was substituted for Cys in the C-terminal Cys-A-A-X element rendered the protein incapable of undergoing isoprenoid modification. In contrast to G gamma 6, the Gi alpha 1 subunit did not appear to undergo isoprenylation when translated in reticulocyte lysate. Transient expression of the protein in COS cells, which were able to isoprenylate the p21 product of transfected H-ras, also failed to demonstrate isoprenylation of Gi alpha 1. The modification of the gamma subunit by a hydrophobic moiety may have important implications for the assembly of the brain G-protein beta gamma complexes into the cell membrane.
脑异源三聚体G蛋白的Giα1和Gγ6亚基的预测氨基酸序列均含有C末端的Cys-A-A-X元件（A为脂肪族残基，X为任意氨基酸）。该结构域是p21ras、核纤层蛋白和真菌交配因子中半胱氨酸经类异戊二烯进行硫醚修饰的位点。我们现在表明，在网织红细胞裂解物中翻译的Gγ6能被类异戊二烯前体[3H]甲羟戊酸有效地标记。改变Gγ6的序列，使C末端Cys-A-A-X元件中的半胱氨酸被甘氨酸取代，导致该蛋白无法进行类异戊二烯修饰。与Gγ6相反，Giα1亚基在网织红细胞裂解物中翻译时似乎未发生异戊二烯化。该蛋白在COS细胞中的瞬时表达也未能证明Giα1的异戊二烯化，而COS细胞能够将转染的H-ras的p21产物异戊二烯化。γ亚基被疏水部分修饰可能对脑G蛋白βγ复合物组装到细胞膜中有重要意义。
