Sandiford Simone L, Slepak Vladlen Z
Department of Molecular and Cellular Pharmacology and Neuroscience Program, University of Miami School of Medicine, 1600 NW 10 Avenue, R-189, Miami, Florida 33136, USA.
Biochemistry. 2009 Mar 17;48(10):2282-9. doi: 10.1021/bi801989c.
Regulators of G protein signaling (RGS) make up a diverse family primarily known as GTPase-activating proteins (GAPs) for heterotrimeric G proteins. In addition to the RGS domain, which is responsible for GAP activity, most RGS proteins contain other distinct structural motifs. For example, members of the R7 family of RGS proteins contain a DEP, GGL, and novel DHEX domain and are obligatory dimers with G protein beta subunit Gbeta5. Here we show that the Gbeta5-RGS7 complex can inhibit Ca2+ mobilization elicited by muscarinic acetylcholine receptor type 3 (M3R), but not by other Gq-coupled receptors such as M1, M5, histamine H1, and GNRH receptors. The isolated DEP domain of RGS7 is sufficient for the inhibition of M3R signaling, whereas the deletion of the DEP domain renders the Gbeta5-RGS7 complex ineffective. Deletion of a portion of the third intracellular loop allowed the receptor (M3R-short) to signal but rendered it insensitive to the effect of the Gbeta5-RGS7 complex. Accordingly, the recombinant DEP domain bound in vitro to the GST-fused i3 loop of the M3R. These results identify a novel molecular mechanism that can impart receptor subtype selectivity on signal transduction via Gq-coupled muscarinic receptors.
G蛋白信号调节因子（RGS）构成了一个多样化的家族，主要作为异源三聚体G蛋白的GTP酶激活蛋白（GAP）为人所知。除了负责GAP活性的RGS结构域外，大多数RGS蛋白还包含其他独特的结构基序。例如，RGS蛋白R7家族的成员包含一个DEP、GGL和新的DHEX结构域，并且是与G蛋白β亚基Gbeta5形成的 obligatory 二聚体。在这里，我们表明Gbeta5-RGS7复合物可以抑制由M3型毒蕈碱乙酰胆碱受体（M3R）引发的Ca2+动员，但不能抑制其他与Gq偶联的受体，如M1、M5、组胺H1和促性腺激素释放激素受体。RGS7分离的DEP结构域足以抑制M3R信号传导，而DEP结构域的缺失使Gbeta5-RGS7复合物无效。删除第三个细胞内环的一部分可使受体（M3R-短）发出信号，但使其对Gbeta5-RGS7复合物的作用不敏感。因此，重组DEP结构域在体外与M3R的GST融合i3环结合。这些结果确定了一种新的分子机制，该机制可以赋予通过与Gq偶联的毒蕈碱受体进行信号转导的受体亚型选择性。
