The effector enzyme regulates the duration of G protein signaling in vertebrate photoreceptors by increasing the affinity between transducin and RGS protein
The effector enzyme regulates the duration of G protein signaling in vertebrate photoreceptors by increasing the affinity between transducin and RGS protein
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DOI：
10.1074/jbc.c000413200
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发表时间：
2000-10-20
影响因子：
4.8
通讯作者：
Arshavsky, VY
中科院分区：
文献类型：
--
作者：
Skiba, NP;Hopp, JA;Arshavsky, VY
光感受器特异性G蛋白转导蛋白作为一个分子开关，刺激其下游GTP结合形式的效应物的活性，并在GTP水解时使效应物失活。这种活性使得转导蛋白GTP酶的速率成为决定脊椎动物视杆和视锥细胞光反应持续时间的重要因素。在光感受器中，G蛋白信号家族调节因子的第9个成员与5型G蛋白β亚基长剪接变体（RGS9-G β 5L）的复合物加速了转导蛋白GTPase缓慢的内在速率。然而，生理上快速的GTPase只有在转导蛋白与其效应物，cGMP磷酸二酯酶（PDE γ）的γ亚基形成复合物时才会被观察到。在本研究中，我们探讨了PDE γ调节转导蛋白GTPase速率的机制，我们发现RGS9-G β 5L单独具有显著的激活转导蛋白GTPase的能力，但其对转导蛋白的亲和力较低。PDEy通过将活化的转导蛋白与RGS9-G β 5L之间的亲和力提高15倍以上而起作用，这从转导蛋白GTPase速率的动力学测量和与固定化转导蛋白的蛋白结合实验中都可以看出。此外，我们的数据表明，单个RGS9-G β 5L分子能够加速GTPase活性，速度接近100个转导蛋白分子/s。这个速率比以前报道的任何RGS蛋白的速率都要快，并且足以在杆状和锥状光感受器中及时恢复光感受器。
The photoreceptor-specific G protein transducin acts as a molecular switch, stimulating the activity of its downstream effector in its GTP-bound form and inactivating the effector upon GTP hydrolysis, This activity makes the rate of transducin GTPase an essential factor in determining the duration of photoresponse in vertebrate rods and cones. In photoreceptors, the slow intrinsic rate of transducin GTPase is accelerated by the complex of the ninth member of the regulators of G protein signaling family with the long splice variant of type 5 G protein beta subunit (RGS9-G beta 5L). However, physiologically rapid GTPase is observed only when transducin forms a complex with its effector, the gamma subunit of cGMP phosphodiesterase (PDE gamma), In this study, we addressed the mechanism by which PDE gamma regulates the rate of transducin GTPase, We found that RGS9-G beta 5L alone has a significant ability to activate transducin GTPase, but its affinity for transducin is low. PDEy acts by enhancing the affinity between activated transducin and RGS9-G beta 5L by more than 15-fold, which is evident both from kinetic measurements of transducin GTPase rate and from protein binding assays with immobilized transducin. Furthermore, our data indicate that a single RGS9-G beta 5L molecule is capable of accelerating the GTPase activity of similar to 100 transducin molecules/s. This rate is faster than the rates reported previously for any RGS protein and is sufficient for timely photoreceptor recovery in both rod and cone photoreceptors.