title: Structural basis for the Rho- and phosphoinositide-dependent localization of the exocyst subunit Sec3.
abstract: The exocyst complex is a hetero-octameric protein complex that functions during cell polarization by tethering the secretory vesicle to the target membrane. The yeast exocyst subunit Sec3 binds to phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P(2)) and the small GTPases Rho1 and Cdc42 via its N-terminal domain (Sec3-N), and these interactions target Sec3 to the plasma membrane. Here we report the crystal structure of the Sec3-N in complex with Rho1 at 2.6-A resolution. Sec3-N adopts a pleckstrin homology (PH) fold, despite having no detectable sequence homology with other PH domains of known structure. Clusters of conserved basic residues constitute a positively charged cleft, which was identified as a binding site for PtdIns(4,5)P(2). Residues Phe77, Ile115 and Leu131 of Sec3 bind to an extended hydrophobic surface formed around switch regions I and II of Rho1. To our knowledge, these are the first structural insights into how an exocyst subunit might interact with both protein and phospholipid factors on the target membrane.
authors.affiliation: Structural Biology Laboratory, Life Science Division, Synchrotron Radiation Research Organization and Institute of Molecular and Cellular Biosciences, The University of Tokyo, Tokyo, Japan.
authors.forename: Masami
authors.initials: M
authors.lastname: Yamashita
authors.forename: Kazuo
authors.initials: K
authors.lastname: Kurokawa
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Sato
authors.forename: Atsushi
authors.initials: A
authors.lastname: Yamagata
authors.forename: Hisatoshi
authors.initials: H
authors.lastname: Mimura
authors.forename: Azusa
authors.initials: A
authors.lastname: Yoshikawa
authors.forename: Ken
authors.initials: K
authors.lastname: Sato
authors.forename: Akihiko
authors.initials: A
authors.lastname: Nakano
authors.forename: Shuya
authors.initials: S
authors.lastname: Fukai
mesh_terms: D018360:Crystallography, X-Ray; D008958:Models, Molecular; D010716:Phosphatidylinositols / Q000378:metabolism*; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism*; D015003:Yeasts / Q000737:chemistry* / Q000378:metabolism*; D020741:rho GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D010716:Phosphatidylinositols; D021122:Protein Subunits; C103130:SEC3 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C051302:RHO1 protein, S cerevisiae; D020741:rho GTP-Binding Proteins