GGL-RGS proteins: bifunctional G-protein regulators

描述（由申请人提供）： G蛋白偶联受体（GPCR）调节关键的生理过程，如神经传递，生长和分化，并且也被大部分治疗剂和娱乐药物靶向。异源三聚体鸟嘌呤核苷酸结合蛋白（G蛋白）在GPCR途径中起分子开关的作用，其中Ga亚基的活性取决于是否结合GTP或GDP。GTP和GDP占有率的相对水平反映了核苷酸交换和GTP水解之间的平衡。前一个反应是由偶联到异源三聚体的GPCR的配体活化催化的，而后一个反应是由GT3活化蛋白或GAPS催化的。G蛋白信号调节子（Regulators of G-protein Signaling，RGS）是作为Ga亚基的GAP的多种蛋白质。RGS蛋白的一个亚家族（RGS 6、7、9、11）含有介导与B亚基结合的Gg样（GGL）结构域。因此，除了通过RGS结构域与GTP-Ga亚基相互作用之外，含有GGL结构域的RGS（GGL-RGS）蛋白还可以与GDP-Ga亚基缔合以促进受体偶联。该项目旨在测试GGL-RGS蛋白分别通过GGL和RGS结构域调节GDP-Ga的受体偶联和GTP-Ga的GTP水解两者的假设，并且这两个结构域的α选择性决定GGL-RGS蛋白对GPCR信号传导的总体效果。为了检验该假设，将确定GUL和RGS结构域两者的Ga选择性，将定义该选择性的分子决定因素，并且将比较野生型和突变体GGL-RGS构建体调节效应子途径的GPCR活化的能力。

DESCRIPTION (provided by applicant): G-protein coupled receptors (GPCRs) regulate critical physiological processes such as neurotransmission, growth, and differentiation, and are also targeted by a large percentage of therapeutic agents and recreational drugs. Heterotrimeric guanine nucleotide binding proteins (G-proteins) act as molecular switches in GPCR pathways, in which the activity of the Ga subunit is determined by whether GTP or GDP is bound. Relative levels of GTP and GDP occupancy reflect the balance between nucleotide exchange and GTP hydrolysis. The former reaction is catalyzed by ligand activation of GPCRs coupled to heterotrimers, while the latter reaction is catalyzed by GTPase activating proteins, or GAPS. Regulators of G-protein Signaling (RGS) are diverse proteins that act as GAPs for Ga subunits. A subfamily of RGS proteins (RGS6, 7, 9, 11) contains a Gg-like (GGL) domain which mediates binding to b subunits. Therefore, in addition to interaction with GTP-Ga subunits through the RGS domain, GGL domain containing RGS (GGL-RGS) proteins may also associate with GDP-Ga subunits to promote receptor coupling. This project is designed to test the hypothesis that GGL-RGS proteins regulate both receptor coupling of GDP-Ga and GTP hydrolysis of GTP-Ga through the GGL and RGS domains, respectively, and that the alpha selectivity of the two domains determine the overall effect of GGL-RGS proteins on GPCR signaling. To test this hypothesis, the Ga selectivity of both the GUL and RGS domains will be determined, the molecular determinants of this selectivity will be defined, and wild type and mutant GGL-RGS constructs will be compared for their ability to regulate GPCR activation of effector pathways.