Smith Benjamin, Hill Claire, Godfrey Emma L, Rand David, van den Berg Hugo, Thornton Steven, Hodgkin Matthew, Davey John, Ladds Graham
Molecular Organization and Assembly of Cells Centre, University of Warwick, Coventry, UK.
Cell Signal. 2009 Jul;21(7):1151-60. doi: 10.1016/j.cellsig.2009.03.004. Epub 2009 Mar 12.
G protein-coupled receptors (GPCRs) regulate a variety of intracellular pathways through their ability to promote the binding of GTP to heterotrimeric G proteins. Regulator of G protein signaling (RGS) proteins increases the intrinsic GTPase activity of Galpha-subunits and are widely regarded as negative regulators of G protein signaling. Using yeast we demonstrate that GTP hydrolysis is not only required for desensitization, but is essential for achieving a high maximal (saturated level) response. Thus RGS-mediated GTP hydrolysis acts as both a negative (low stimulation) and positive (high stimulation) regulator of signaling. To account for this we generated a new kinetic model of the G protein cycle where Galpha(GTP) enters an inactive GTP-bound state following effector activation. Furthermore, in vivo and in silico experimentation demonstrates that maximum signaling output first increases and then decreases with RGS concentration. This unimodal, non-monotone dependence on RGS concentration is novel. Analysis of the kinetic model has revealed a dynamic network motif that shows precisely how inclusion of the inactive GTP-bound state for the Galpha produces this unimodal relationship.
G蛋白偶联受体（GPCRs）通过促进GTP与异源三聚体G蛋白结合的能力来调节多种细胞内信号通路。G蛋白信号调节蛋白（RGS）可提高Gα亚基的内在GTP酶活性，被广泛认为是G蛋白信号的负调节因子。我们利用酵母证明，GTP水解不仅是脱敏所必需的，而且对于实现高最大（饱和水平）反应至关重要。因此，RGS介导的GTP水解既是信号传导的负（低刺激）调节因子，也是正（高刺激）调节因子。为了解释这一点，我们构建了一个新的G蛋白循环动力学模型，其中Gα（GTP）在效应器激活后进入无活性的GTP结合状态。此外，体内和计算机模拟实验表明，最大信号输出首先随RGS浓度增加，然后随其浓度降低。这种对RGS浓度的单峰、非单调依赖性是新颖的。对动力学模型的分析揭示了一个动态网络基序，精确显示了Gα的无活性GTP结合状态如何产生这种单峰关系。
