title: The PHCCEx domain of Tiam1/2 is a novel protein- and membrane-binding module.
abstract: Tiam1 and Tiam2 (Tiam1/2) are guanine nucleotide-exchange factors that possess the PH-CC-Ex (pleckstrin homology, coiled coil and extra) region that mediates binding to plasma membranes and signalling proteins in the activation of Rac GTPases. Crystal structures of the PH-CC-Ex regions revealed a single globular domain, PHCCEx domain, comprising a conventional PH subdomain associated with an antiparallel coiled coil of CC subdomain and a novel three-helical globular Ex subdomain. The PH subdomain resembles the beta-spectrin PH domain, suggesting non-canonical phosphatidylinositol binding. Mutational and binding studies indicated that CC and Ex subdomains form a positively charged surface for protein binding. We identified two unique acidic sequence motifs in Tiam1/2-interacting proteins for binding to PHCCEx domain, Motif-I in CD44 and ephrinB's and the NMDA receptor, and Motif-II in Par3 and JIP2. Our results suggest the molecular basis by which the Tiam1/2 PHCCEx domain facilitates dual binding to membranes and signalling proteins.
authors.affiliation: Structural Biology Laboratory, Nara Institute of Science and Technology, Takayama, Ikoma, Nara, Japan.
authors.forename: Shin-ichi
authors.initials: S
authors.lastname: Terawaki
authors.forename: Ken
authors.initials: K
authors.lastname: Kitano
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Mori
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhai
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Higuchi
authors.forename: Norimichi
authors.initials: N
authors.lastname: Itoh
authors.forename: Takashi
authors.initials: T
authors.lastname: Watanabe
authors.forename: Kozo
authors.initials: K
authors.lastname: Kaibuchi
authors.forename: Toshio
authors.initials: T
authors.lastname: Hakoshima
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D018360:Crystallography, X-Ray; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D018960:Hyaluronan Receptors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D066298:In Vitro Techniques; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017510:Protein Folding; D054730:Protein Interaction Domains and Motifs; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1
chemical_list: C476399:Cd44 protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D018960:Hyaluronan Receptors; D011994:Recombinant Proteins; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; C513260:Tiam1 protein, mouse; C447620:Tiam2 protein, mouse