IQGAP1 Structure and Function

描述(申请人提供)：IQGAP1是一个190kD的胞浆蛋白支架，具有几个蛋白质相互作用结构域。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激酶信号组件和细胞连接蛋白。虽然细节还不是很清楚，但通过不同的相互作用，IQGAP1在许多过程中发挥了重要作用，包括定义细胞极性、定向细胞迁移和细胞侵袭。有越来越多的间接证据表明IQGAP1参与了癌症的发生，并且IQGAP1在几种不同的肿瘤中过表达。在其他有趣的观察中，IQGAP1的过度表达已被证明破坏了基于钙粘素的细胞-细胞连接的稳定性，并以一种rac1/CDc42依赖的方式增加了细胞的运动性和侵袭性。目前，关于IQGAP1及其蛋白质-蛋白质相互作用的结构信息很少。然而，一些观察结果表明，IQGAP1不是一个仅仅收集信号组件的被动支架。首先，IQGAP1的寡聚是正常功能所必需的。第二，IQGAP1是Rho家族GTPase rac1和CDc42的一个新的效应器，激活的CDc42的结合促进了二聚体的形成，并调节了IQGAP1 C末端介导的相互作用。第三，在IQGAP1 GAP相关结构域(GRD)中引入17个残基的突变赋予了一种“结构性活性”表型；IQGAP1分子的行为就像与活性CDC42结合一样。17个残基插入位于GRD的表面，如果结合方式类似于RAS？RasGAP相互作用，则GRD将与GTP酶结合。最后，IQGAP1氨基末端残基反式抑制了IQGAP1 C末端与N-WASP的相互作用。基于这些和其他观察，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需的结合决定因素。本建议的重点是阐明IQGAP1的三级结构和IQGAP1的S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.