Gurevich V V, Pals-Rylaarsdam R, Benovic J L, Hosey M M, Onorato J J
Sun Health Research Institute, Sun City, Arizona 85372, USA.
J Biol Chem. 1997 Nov 14;272(46):28849-52. doi: 10.1074/jbc.272.46.28849.
The rapid decrease of a response to a persistent stimulus, often termed desensitization, is a widespread biological phenomenon. Signal transduction by numerous G protein-coupled receptors appears to be terminated by a strikingly uniform two-step mechanism, most extensively characterized for the beta2-adrenergic receptor (beta2AR), m2 muscarinic cholinergic receptor (m2 mAChR), and rhodopsin. The model predicts that activated receptor is initially phosphorylated and then tightly binds an arrestin protein that effectively blocks further G protein interaction. Here we report that complexes of beta2AR-arrestin and m2 mAChR-arrestin have a higher affinity for agonists (but not antagonists) than do receptors not complexed with arrestin. The percentage of phosphorylated beta2AR in this high affinity state in the presence of full agonists varied with different arrestins and was enhanced by selective mutations in arrestins. The percentage of high affinity sites also was proportional to the intrinsic activity of an agonist, and the coefficient of proportionality varies for different arrestin proteins. Certain mutant arrestins can form these high affinity complexes with unphosphorylated receptors. Mutations that enhance formation of the agonist-receptor-arrestin complexes should provide useful tools for manipulating both the efficiency of signaling and rate and specificity of receptor internalization.
对持续刺激的反应迅速减弱，通常称为脱敏，是一种广泛存在的生物学现象。众多G蛋白偶联受体的信号转导似乎通过一种极为统一的两步机制终止，其中对β2肾上腺素能受体（β2AR）、M2毒蕈碱胆碱能受体（M2 mAChR）和视紫红质的研究最为深入。该模型预测，活化的受体首先被磷酸化，然后紧密结合一种抑制蛋白，从而有效地阻断进一步的G蛋白相互作用。在此我们报告，与未与抑制蛋白结合的受体相比，β2AR-抑制蛋白和M2 mAChR-抑制蛋白复合物对激动剂（而非拮抗剂）具有更高的亲和力。在存在完全激动剂的情况下，处于这种高亲和力状态的磷酸化β2AR的百分比因不同的抑制蛋白而异，并通过抑制蛋白中的选择性突变而增加。高亲和力位点的百分比也与激动剂的内在活性成正比，且不同抑制蛋白的比例系数有所不同。某些突变的抑制蛋白可与未磷酸化的受体形成这些高亲和力复合物。增强激动剂-受体-抑制蛋白复合物形成的突变应为操纵信号转导效率以及受体内化的速率和特异性提供有用的工具。
