Paz M M, Ramos M, Ramírez G, Souza D
Departamento de Bioquímica, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil.
FEBS Lett. 1994 Nov 28;355(2):205-8. doi: 10.1016/0014-5793(94)01208-3.
In G protein-coupled receptors, neurotransmitter-induced binding of GTP to G proteins triggers the activation of effector systems while simultaneously decreasing the affinity of the transmitter for its specific binding site within the receptor-G protein complex. In the present study we show that, in the chick optic tectum, guanine nucleotides inhibit the binding of the glutamate analog, kainate, and activate adenylate cyclase by different mechanisms and acting on different sites. GMP-PNP, a non-hydrolyzable analog of GTP, binds tightly to G proteins so that the binding is stable even after exhaustive washing. By use of this property, we have prepared membrane samples in which G protein GTP-binding sites are pre-saturated with GMP-PNP. Experiments carried out with these membranes show that GMP-PNP, GDP-S and GMP inhibit the binding of [3H]kainate by interacting with site(s) unrelated to G proteins, whereas GMP-PNP activates adenylate cyclase activity by binding to G proteins.
在G蛋白偶联受体中，神经递质诱导的GTP与G蛋白结合会触发效应系统的激活，同时降低递质对受体-G蛋白复合物内其特异性结合位点的亲和力。在本研究中，我们表明，在鸡视顶盖中，鸟嘌呤核苷酸通过不同机制并作用于不同位点抑制谷氨酸类似物海人酸的结合并激活腺苷酸环化酶。GMP-PNP是一种不可水解的GTP类似物，它与G蛋白紧密结合，以至于即使经过彻底洗涤，结合仍很稳定。利用这一特性，我们制备了膜样品，其中G蛋白的GTP结合位点被GMP-PNP预饱和。用这些膜进行的实验表明，GMP-PNP、GDP-S和GMP通过与G蛋白无关的位点相互作用来抑制[3H]海人酸的结合，而GMP-PNP通过与G蛋白结合来激活腺苷酸环化酶活性。
