GBeta5/RGS proteins and GPCR signaling

描述(申请人提供)：G蛋白信号转导调节蛋白(RGS)最初被鉴定为异源三聚体G蛋白的GTP酶激活蛋白(GAP)？亚单位。然而，许多RGS蛋白除了具有签名的RGS盒外，还具有高度保守的结构域，这赋予了一个多功能的特性，该特性是异源三聚体G蛋白信号级联以及与其他信号通路之间相互作用的基础，虽然了解不多，但在生理上具有重要的作用。R7亚家族的RGS蛋白具有一个独特的G？样(GGL)结构域，该结构域介导与非典型G蛋白亚基G？5形成特异性和专性异二聚体，提示这些信号蛋白具有与传统G？？二聚体。我们最近改进的G？5/RGS9晶体结构支持这一观点，并为测试与这种二聚体的各种结合界面相关的假说提供了一个框架，这些假说可能有助于更高顺序、多功能的G蛋白/GPCR/RGS复合体的组织和整合。因此，我们建议：1)使用结晶学和突变分析来定义完整的官能团和G？2)扩大了我们对G？5/R7二聚体及其锚定蛋白R9AP和R7BP之间的功能和结构关系的理解；3)量化了G？5/R7二聚体与GDP-G？使用重组的纯化组分系统的亚基和GPCRs。虽然很明显，在各种生理环境下，R7蛋白是由G蛋白偶联受体介导的正确信号传递所必需的，但这些蛋白在协调这些信号事件中的作用相对较少。这里提出的工作旨在将R7蛋白置于关于G蛋白偶联受体和异源三聚体G蛋白的详细结构和功能背景中。预计这些研究将在R7蛋白介导的协调信号失败的情况下用于指导治疗方案。

DESCRIPTION (provided by applicant): The Regulator of G protein Signaling (RGS) proteins originally were identified as GTPase-activating proteins (GAPs) for heterotrimeric G protein ? subunits. However, many RGS proteins possess highly- conserved domains in addition to the signature RGS box, which empower a multifunctional character that underlies poorly understood but physiologically important interactions among components of heterotrimeric G protein signaling cascades as well as with other signaling pathways. The R7 subfamily of RGS proteins possess a distinctive G-?-like (GGL) domain that mediates specific and obligate heterodimer formation with the atypical G protein subunit, G?5, suggesting that these signaling proteins exhibit functions similar to conventional G?? dimers. Our recently refined crystal structure of G?5/RGS9 support this idea and provides a framework for testing hypotheses related to various binding interfaces of this dimer that likely subserve the organization and integration of higher-order, multifunctional G protein/GPCR/RGS complexes. Consequently, we propose to: 1) use crystallography and mutational analyses to define the complete functionality and G? specificity of RGS domains within full-length G??5/R7 dimers; 2) extend our understanding of the functional and structural relationships between G??5/R7 dimers and their anchoring proteins, R9AP and R7BP; and 3) quantify the functional capacities of G??5/R7 dimers to interact with GDP- G? subunits and GPCRs using reconstituted systems of purified components. While it is clear that R7 proteins are required for proper signaling mediated by G protein-coupled receptors under a variety of physiological settings, the roles of these proteins in coordinating these signaling events are relatively poorly understood. The work proposed here is designed to place R7 proteins within a detailed structural and functional context with respect to G protein-coupled receptors and heterotrimeric G proteins. It is anticipated that these studies will then be used to guide treatment regimens in cases where coordinated signaling mediated by R7 proteins has failed.