title: IQGAP proteins reveal an atypical phosphoinositide (aPI) binding domain with a pseudo C2 domain fold.
abstract: Class I phosphoinositide (PI) 3-kinases act through effector proteins whose 3-PI selectivity is mediated by a limited repertoire of structurally defined, lipid recognition domains. We describe here the lipid preferences and crystal structure of a new class of PI binding modules exemplified by select IQGAPs (IQ motif containing GTPase-activating proteins) known to coordinate cellular signaling events and cytoskeletal dynamics. This module is defined by a C-terminal 105-107 amino acid region of which IQGAP1 and -2, but not IQGAP3, binds preferentially to phosphatidylinositol 3,4,5-trisphosphate (PtdInsP(3)). The binding affinity for PtdInsP(3), together with other, secondary target-recognition characteristics, are comparable with those of the pleckstrin homology domain of cytohesin-3 (general receptor for phosphoinositides 1), an established PtdInsP(3) effector protein. Importantly, the IQGAP1 C-terminal domain and the cytohesin-3 pleckstrin homology domain, each tagged with enhanced green fluorescent protein, were both re-localized from the cytosol to the cell periphery following the activation of PI 3-kinase in Swiss 3T3 fibroblasts, consistent with their common, selective recognition of endogenous 3-PI(s). The crystal structure of the C-terminal IQGAP2 PI binding module reveals unexpected topological similarity to an integral fold of C2 domains, including a putative basic binding pocket. We propose that this module integrates select IQGAP proteins with PI 3-kinase signaling and constitutes a novel, atypical phosphoinositide binding domain that may represent the first of a larger group, each perhaps structurally unique but collectively dissimilar from the known PI recognition modules.
authors.affiliation: Division of Cell Signalling and Immunology, College of Life Sciences, University of Dundee, Dow St., Dundee DD1 5EH, Scotland, United Kingdom.
authors.forename: Miles J
authors.initials: MJ
authors.lastname: Dixon
authors.forename: Alexander
authors.initials: A
authors.lastname: Gray
authors.forename: Martijn
authors.initials: M
authors.lastname: Schenning
authors.forename: Mark
authors.initials: M
authors.lastname: Agacan
authors.forename: Wolfram
authors.initials: W
authors.lastname: Tempel
authors.forename: Yufeng
authors.initials: Y
authors.lastname: Tong
authors.forename: Lyudmila
authors.initials: L
authors.lastname: Nedyalkova
authors.forename: Hee-Won
authors.initials: HW
authors.lastname: Park
authors.forename: Nicholas R
authors.initials: NR
authors.lastname: Leslie
authors.forename: Daan M F
authors.initials: DM
authors.lastname: van Aalten
authors.forename: C Peter
authors.initials: CP
authors.lastname: Downes
authors.forename: Ian H
authors.initials: IH
authors.lastname: Batty
mesh_terms: D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D003461:Crystallography; D020690:GTPase-Activating Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D015398:Signal Transduction / Q000502:physiology*; D020703:ras GTPase-Activating Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D020690:GTPase-Activating Proteins; C101203:IQ motif containing GTPase activating protein 1; C531126:IQGAP3 protein, mouse; C484416:Iqgap2 protein, mouse; D010716:Phosphatidylinositols; D020703:ras GTPase-Activating Proteins; D019869:Phosphatidylinositol 3-Kinases