IQGAP1 Structure and Function

描述（由申请人提供）：IQGAP1是一个190kD的细胞质蛋白支架，具有多个蛋白相互作用结构域。最近的研究结果将IQGAP1与许多蛋白质联系起来，包括生长因子受体、MAP激酶信号成分和细胞连接蛋白。尽管细节尚不清楚，但通过多种相互作用，IQGAP1在许多过程中发挥重要作用，包括细胞极性的定义，定向细胞迁移和细胞侵袭。越来越多的间接证据表明，IQGAP1参与了癌症的发生，并且在几种不同的肿瘤中，IQGAP1过表达。在其他有趣的观察结果中，IQGAP1的过表达已被证明以依赖于Rac1/ cdc42的方式破坏基于钙粘蛋白的细胞-细胞连接的稳定性，增加细胞的运动性和侵袭性。目前，关于IQGAP1及其蛋白-蛋白相互作用的结构信息很少。然而，一些观察表明，IQGAP1并不是一个仅仅收集信号成分的被动支架。首先，IQGAP1的寡聚化是正常功能所必需的。其次，IQGAP1是rho家族GTPases Rac1和Cdc42的新型效应体，与活化的Cdc42结合可增强二聚体的形成，并调节由IQGAP1 c端介导的相互作用。第三，在IQGAP1 gap相关结构域（GRD）内引入17个残基的突变赋予“构成活性”表型；IQGAP1分子的行为似乎与活性Cdc42结合。17个残基插入位于GRD表面，如果结合方式与Ras？RasGAP交互。最后，在反式中，IQGAP1氨基末端残基抑制了IQGAP1 c端与N-WASP之间的相互作用。基于这些和其他观察结果，我们认为通过不同的分子间和分子内相互作用，IQGAP1暴露和隐藏了调节其功能所必需的结合决定因素。本提案的重点是阐明IQGAP1的三级结构以及IQGAP1与结合伙伴相互作用的结构要求。

DESCRIPTION (provided by applicant): IQGAP1 is a 190kD cytosolic protein scaffold that possesses several protein-protein interaction domains. The results of recent research link IQGAP1 to numerous proteins including growth factor receptors, MAP kinase signaling components, and cell junction proteins. Although the details are not well understood, through diverse interactions IQGAP1 has an important role in numerous processes including the definition of cell polarity, directed cell migration, and cell invasion. There is a growing body of circumstantial evidence that IQGAP1 is involved in carcinogenesis, and IQGAP1 is overexpressed in several different neoplasms. Among other intriguing observations, over-expression of IQGAP1 has been shown to destabilize cadherin-based cell-cell junctions and increase cell motility and invasiveness in a Rac1/Cdc42-dependent manner. Currently, there is very little structural information for IQGAP1 and its protein-protein interactions. However, several observations imply that IQGAP1 is not a passive scaffold that merely collects signaling components. First, the oligomerization of IQGAP1 is required for normal function. Second, IQGAP1 is a novel effector of the Rho-family GTPases Rac1 and Cdc42 and binding of activated Cdc42 enhances dimer formation and modulates interactions mediated by the IQGAP1 C-terminus. Third, a mutation that introduces 17 residues within the IQGAP1 GAP-related domain (GRD) confers a "constitutively-active" phenotype; IQGAP1 molecules that behave as though bound to active Cdc42. The 17 residue insertion is located on the surface of the GRD that would bind GTPases if the mode of binding is similar to the Ras?RasGAP interaction. Lastly, IQGAP1 amino terminal residues inhibit in trans the interaction between the IQGAP1 C-terminus and N-WASP. Based on these and other observations, we believe that through diverse inter- and intramolecular interactions, IQGAP1 exposes and conceals binding determinants necessary for the regulation of its functions. The focus of this proposal is to elucidate the IQGAP1 tertiary structure and the structural requirements for IQGAP1's interactions with binding partners. PUBLIC HEALTH RELEVANCE: IQGAP1, a large molecular scaffold that interacts with numerous cellular proteins, is over-expressed in some cancers, and has been shown to increase cell motility and invasive potential, and to regulate cell-cell interactions. These observations are consistent with the notion that IQGAP1 activity may be required for cancer cells to leave a primary tumor and invade distant tissues. This proposal is designed to provide much needed structural information as it pertains to IQGAP1 function.