Crystal Structure of the GTPase-activating Protein-related Domain from IQGAP1

ArticleinJournal of Biological Chemistry 284(22):14857-65 · April 2009with7 Reads
DOI: 10.1074/jbc.M808974200 · Source: PubMed
Abstract
IQGAP1 is a 190-kDa molecular scaffold containing several domains required for interaction with numerous proteins. One domain is homologous to Ras GTPase-activating protein (GAP) domains. However, instead of accelerating hydrolysis of bound GTP on Ras IQGAP1, using its GAP-related domain (GRD) binds to Cdc42 and Rac1 and stabilizes their GTP-bound states. We report here the crystal structure of the isolated IQGAP1 GRD. Despite low sequence conservation, the overall structure of the GRD is very similar to the GAP domains from p120 RasGAP, neurofibromin, and SynGAP. However, instead of the catalytic "arginine finger" seen in functional Ras GAPs, the GRD has a conserved threonine residue. GRD residues 1099-1129 have no structural equivalent in RasGAP and are seen to form an extension at one end of the molecule. Because the sequence of these residues is highly conserved, this region likely confers a functionality particular to IQGAP family GRDs. We have used isothermal titration calorimetry to demonstrate that the isolated GRD binds to active Cdc42. Assuming a mode of interaction similar to that displayed in the Ras-RasGAP complex, we created an energy-minimized model of Cdc42.GTP bound to the GRD. Residues of the GRD that contact Cdc42 map to the surface of the GRD that displays the highest level of sequence conservation. The model indicates that steric clash between threonine 1046 with the phosphate-binding loop and other subtle changes would likely disrupt the proper geometry required for GTP hydrolysis.
    • "IQGAP1 was originally identified as a molecule with four calmodulinbinding IQ motifs and a GAP domain for Ras (Weissbach et al. 1994). The name " IQGAP " originates as a result of this domain organization, but no report has convincingly demonstrated its GAP activity toward any small GTPases, which is in agreement with the finding that the GAP domain of IQGAPs lacks the arginine finger that is critical for GAP activity (Kurella et al. 2009). Subsequent studies revealed IQGAP1 to be an effector of Rac1 and Cdc42, and the GRD domain in IQGAP1 was later shown to stabilize Rac1 and Cdc42 in the GTP-bound active form (Noritake et al. 2005; White et al. 2012). "
    [Show abstract] [Hide abstract] ABSTRACT: The actin-cytoskeleton plays a critical role in various biological processes, including cell migration, development, tissue remodeling, and memory formation. Both extracellular and intracellular signals regulate reorganization of the actin-cytoskeleton to modulate tissue architecture and cellular morphology in a spatiotemporal manner. Since the discovery that activation of Rho family GTPases induces actin-cytoskeleton reorganization, the mode of action of Rho family GTPases has been extensively studied and individual effectors have been characterized. The actin-binding protein IQGAP1 was identified as an effector of Rac and Cdc42 and is the founding member of the IQGAP family with two additional isoforms. The IQGAP family shows conserved domain organization, and each member displays a specific expression pattern in mammalian tissues. IQGAPs regulate the actin-cytoskeleton alone and with their binding partners, thereby controlling diverse cellular processes, such as cell migration and adhesion. Here, we introduce IQGAPs as an actin-cytoskeleton regulator.
    Full-text · Article · Jun 2015
    • "The threonine 1046 residue thought to be related to the absence of GAP function is outlined in red. Amino acids involved in the -helix structure (Kurella et al., 2009) This phosphorylation (probably through a conformational change) results in the release of Clasp2 from IQGAP1/EB1/microtubule/actin complexes at the leading edges of cells, restricting their movement (Watanabe et al., 2009). Further, IQGAP1 is known to interact with Lis1, a dynein motor complex-interacting protein. "
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    Full-text · Article · Feb 2015
    • "The GRD domain is similar with the functional subunit of GAPs (Ras GTPase-activating proteins). However, the function is different, it binds Rac1 and cdc42 and stabilizes the GTP-bound active state of Rho GTPases [14]. The C-terminal RasGAP_c carboxyl sequence is capable of binding with E-cadherin and Beta-catenin [12]. "
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