title: Conserved sequence repeats of IQGAP1 mediate binding to Ezrin.
abstract: Mammalian IQGAP proteins all feature multiple ∼50 amino acid sequence repeats near their N-termini, and little is known about the function of these "Repeats". We have expressed and purified the Repeats from human IQGAP1 to identify binding partners. We used mass spectrometry to identify 42 mouse kidney proteins that associate with the IQGAP1 Repeats including the ERM proteins ezrin, radixin, and moesin. ERM proteins have an N-terminal FERM domain (4.1, ezrin, radixin, moesin) through which they bind to protein targets and phosphatidylinositol 4,5-bisphosphate (PIP2) and a C-terminal actin-binding domain and function to link the actin cytoskeleton to distinct locations on the cell cortex. Isothermal titration calorimetry (ITC) reveals that the IQGAP1 Repeats directly bind to the ezrin FERM domain, while no binding is seen for full-length "autoinhibited" ezrin or a version of full-length ezrin intended to mimic the activated protein. ITC also indicates that the ezrin FERM domain binds to the Repeats from IQGAP2 but not the Repeats from IQGAP3. We conclude that IQGAP1 and IQGAP2 are positioned at the cell cortex by ERM proteins. We propose that the IQGAP3 Repeats may likewise bind to FERM domains for signaling purposes.
authors.affiliation: Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center , 1901 Perdido Street, New Orleans, Louisiana 70112, United States.
authors.forename: Jing
authors.initials: J
authors.lastname: Liu
authors.forename: Jesse J
authors.initials: JJ
authors.lastname: Guidry
authors.forename: David K
authors.initials: DK
authors.lastname: Worthylake
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002151:Calorimetry; D017124:Conserved Sequence; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D018076:DNA, Complementary / Q000235:genetics; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D051379:Mice; D016133:Polymerase Chain Reaction; D011485:Protein Binding; D020449:Repetitive Sequences, Amino Acid; D053719:Tandem Mass Spectrometry; D020703:ras GTPase-Activating Proteins / Q000737:chemistry* / Q000378:metabolism; D000099149:Ezrin
chemical_list: D003598:Cytoskeletal Proteins; D018076:DNA, Complementary; D020703:ras GTPase-Activating Proteins; D000099149:Ezrin; C101203:IQ motif containing GTPase activating protein 1