title: GIT1 utilizes a focal adhesion targeting-homology domain to bind paxillin.
abstract: The GIT proteins, GIT1 and GIT2, are GTPase-activating proteins for the ADP-ribosylation factor family of small GTP-binding proteins, but also serve as adaptors to link signaling proteins to distinct cellular locations. One role for GIT proteins is to link the PIX family of Rho guanine nucleotide exchange factors and their binding partners, the p21-activated protein kinases, to remodeling focal adhesions by interacting with the focal adhesion adaptor protein paxillin. We here identified the C-terminal domain of GIT1 responsible for paxillin binding. Combining structural and mutational analyses, we show that this region folds into an anti-parallel four-helix domain highly reminiscent to the focal adhesion targeting (FAT) domain of focal adhesion kinase (FAK). Our results suggest that the GIT1 FAT-homology (FAH) domain and FAT bind the paxillin LD4 motif quite similarly. Since only a small fraction of GIT1 is bound to paxillin under normal conditions, regulation of paxillin binding was explored. Although paxillin binding to the FAT domain of FAK is regulated by tyrosine phosphorylation within this domain, we find that tyrosine phosphorylation of the FAH domain GIT1 is not involved in regulating binding to paxillin. Instead, we find that mutations within the FAH domain may alter binding to paxillin that has been phosphorylated within the LD4 motif. Thus, despite apparent structural similarity in their FAT domains, GIT1 and FAK binding to paxillin is differentially regulated.
authors.affiliation: Division of Gastroenterology, Department of Medicine, Duke University Medical Center, Durham, NC 27710, United States.
authors.forename: Robert
authors.initials: R
authors.lastname: Schmalzigaug
authors.forename: Marie-Line
authors.initials: ML
authors.lastname: Garron
authors.forename: J Tyler
authors.initials: JT
authors.lastname: Roseman
authors.forename: Yanghui
authors.initials: Y
authors.lastname: Xing
authors.forename: Collin E
authors.initials: CE
authors.lastname: Davidson
authors.forename: Stefan T
authors.initials: ST
authors.lastname: Arold
authors.forename: Richard T
authors.initials: RT
authors.lastname: Premont
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D018797:Cell Cycle Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002522:Chlorocebus aethiops; D022001:Focal Adhesions / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D051419:Paxillin / Q000378:metabolism*; D017354:Point Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; C485647:GIT1 protein, human; D051419:Paxillin