Albert Eye Research Institute, Duke University, Durham, North Carolina 27710, USA.
J Neurosci. 2011 Oct 12;31(41):14660-8. doi: 10.1523/JNEUROSCI.3516-11.2011.
The members of the R7 regulator of G-protein signaling (RGS) protein subfamily are versatile regulators of G-protein signaling throughout the nervous system. Recent studies indicate that they are often found in complexes with membrane anchor proteins that serve as versatile modulators of their activity, intracellular targeting, and stability. One striking example is the interplay between the membrane anchor R9AP and the RGS9-1 · Gβ5 GTPase-activating complex responsible for the rapid inactivation of the G-protein transducin in vertebrate photoreceptor cells during their recovery from light excitation. The amount of this complex in photoreceptors sets their temporal resolution and is precisely regulated by the expression level of R9AP, which serves to protect the RGS9-1 and Gβ5 subunits from intracellular proteolysis. In this study, we investigated the mechanism by which R9AP performs its protective function in mouse rods and found that it is entirely confined to recruiting RGS9-1 · Gβ5 to cellular membranes. Furthermore, membrane attachment of RGS9-1 · Gβ5 is sufficient for its stable expression in rods even in the absence of R9AP. Our second finding is that RGS9-1 · Gβ5 possesses targeting information that specifies its exclusion from the outer segment and that this information is neutralized by association with R9AP to allow outer segment targeting. Finally, we demonstrate that the ability of R9AP · RGS9-1 · Gβ5 to accelerate GTP hydrolysis on transducin is independent of its means of membrane attachment, since replacing the transmembrane domain of R9AP with a site for lipid modification did not impair the catalytic activity of this complex.
R7 调节蛋白信号转导(RGS)蛋白亚家族的成员是神经系统中 G 蛋白信号转导的多功能调节剂。最近的研究表明,它们通常与膜锚定蛋白形成复合物,这些蛋白作为其活性、细胞内靶向和稳定性的多功能调节剂。一个引人注目的例子是膜锚定蛋白 R9AP 与 RGS9-1·Gβ5 GTP 酶激活复合物之间的相互作用,该复合物负责脊椎动物光感受器细胞在从光激发中恢复时快速失活 G 蛋白转导蛋白。该复合物在光感受器中的数量决定了它们的时间分辨率,并受到 R9AP 表达水平的精确调节,R9AP 可防止 RGS9-1 和 Gβ5 亚基发生细胞内蛋白水解。在这项研究中,我们研究了 R9AP 在小鼠视杆细胞中发挥保护功能的机制,发现它完全局限于将 RGS9-1·Gβ5 募集到细胞膜上。此外,即使在没有 R9AP 的情况下,RGS9-1·Gβ5 的膜附着也足以使其在视杆细胞中稳定表达。我们的第二个发现是,RGS9-1·Gβ5 具有指定其从外节排除的靶向信息,并且该信息通过与 R9AP 结合而中和,从而允许外节靶向。最后,我们证明了 R9AP·RGS9-1·Gβ5 加速转导蛋白上 GTP 水解的能力与其膜附着方式无关,因为用脂质修饰的位点替换 R9AP 的跨膜结构域不会损害该复合物的催化活性。