Kovoor A, Chen C K, He W, Wensel T G, Simon M I, Lester H A
Division of Biology, California Institute of Technology, Pasadena, California 91125, USA.
J Biol Chem. 2000 Feb 4;275(5):3397-402. doi: 10.1074/jbc.275.5.3397.
Regulators of G protein signaling (RGS) stimulate the GTPase activity of G protein Galpha subunits and probably play additional roles. Some RGS proteins contain a Ggamma subunit-like (GGL) domain, which mediates a specific interaction with Gbeta5. The role of such interactions in RGS function is unclear. RGS proteins can accelerate the kinetics of coupling of G protein-coupled receptors to G-protein-gated inwardly rectifying K(+) (GIRK) channels. Therefore, we coupled m2-muscarinic acetylcholine receptors to GIRK channels in Xenopus oocytes to evaluate the effect of Gbeta5 on RGS function. Co-expression of either RGS7 or RGS9 modestly accelerated GIRK channel kinetics. When Gbeta5 was co-expressed with either RGS7 or RGS9, the acceleration of GIRK channel kinetics was strongly increased over that produced by RGS7 or RGS9 alone. RGS function was not enhanced by co-expression of Gbeta1, and co-expression of Gbeta5 alone had no effect on GIRK channel kinetics. Gbeta5 did not modulate the function either of RGS4, an RGS protein that lacks a GGL domain, or of a functional RGS7 construct in which the GGL domain was omitted. Enhancement of RGS7 function by Gbeta5 was not a consequence of an increase in the amount of plasma membrane or cytosolic RGS7 protein.
G蛋白信号调节因子（RGS）可刺激G蛋白α亚基的GTP酶活性，可能还发挥其他作用。一些RGS蛋白含有一个类Gγ亚基（GGL）结构域，该结构域介导与Gβ5的特异性相互作用。此类相互作用在RGS功能中的作用尚不清楚。RGS蛋白可加速G蛋白偶联受体与G蛋白门控内向整流钾通道（GIRK）的偶联动力学。因此，我们将毒蕈碱型乙酰胆碱m2受体与非洲爪蟾卵母细胞中的GIRK通道偶联，以评估Gβ5对RGS功能的影响。共表达RGS7或RGS9可适度加速GIRK通道动力学。当Gβ5与RGS7或RGS9共表达时，GIRK通道动力学的加速程度比单独由RGS7或RGS9产生的加速程度大幅增加。共表达Gβ1不会增强RGS功能，单独共表达Gβ5对GIRK通道动力学没有影响。Gβ5对缺乏GGL结构域的RGS蛋白RGS4或缺失GGL结构域的功能性RGS7构建体的功能均无调节作用。Gβ5对RGS7功能的增强并非质膜或胞质RGS7蛋白量增加的结果。
