title: Structural basis for recognition of the Sec4 Rab GTPase by its effector, the Lgl/tomosyn homologue, Sro7.
abstract: Members of the tomosyn/Lgl/Sro7 family play important roles in vesicle trafficking and cell polarity in eukaryotic cells. The yeast homologue, Sro7, is believed to act as a downstream effector of the Sec4 Rab GTPase to promote soluble N-ethylmaleimide-sensitive factor adaptor protein receptor (SNARE) assembly during Golgi-to-cell surface vesicle transport. Here we describe the identification of a Sec4 binding site on the surface of Sro7 that is contained within a cleft created by the junction of two adjacent β-propellers that form the core structure of Sro7. Computational docking experiments suggested four models for interaction of GTP-Sec4 with the Sro7 binding cleft. Further mutational and biochemical analyses confirmed that only one of the four docking arrangements is perfectly consistent with our genetic and biochemical interaction data. Close examination of this docking model suggests a structural basis for the high substrate and nucleotide selectivity in effector binding by Sro7. Finally, analysis of the surface variation within the homologous interaction site on tomosyn-1 and Lgl-1 structural models suggests a possible conserved Rab GTPase effector function in tomosyn vertebrate homologues.
authors.affiliation: Department of Cell Biology and Physiology, University of North Carolina School of Medicine, Chapel Hill, NC 27599 Graduate Program in Cell and Developmental Biology, University of North Carolina School of Medicine, Chapel Hill, NC 27599.
authors.forename: Kelly
authors.initials: K
authors.lastname: Watson
authors.affiliation: Department of Cell Biology and Physiology, University of North Carolina School of Medicine, Chapel Hill, NC 27599.
authors.forename: Guendalina
authors.initials: G
authors.lastname: Rossi
authors.affiliation: Department of Biochemistry and Biophysics, University of North Carolina School of Medicine, Chapel Hill, NC 27599 R. L. Juliano Structural Bioinformatics Core, University of North Carolina School of Medicine, Chapel Hill, NC 27599.
authors.forename: Brenda
authors.initials: B
authors.lastname: Temple
authors.affiliation: Department of Cell Biology and Physiology, University of North Carolina School of Medicine, Chapel Hill, NC 27599 Graduate Program in Cell and Developmental Biology, University of North Carolina School of Medicine, Chapel Hill, NC 27599 pjbrennw@med.unc.edu.
authors.forename: Patrick
authors.initials: P
authors.lastname: Brennwald
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D001665:Binding Sites; D006160:Guanosine Triphosphate / Q000378:metabolism; D062105:Molecular Docking Simulation; D008969:Molecular Sequence Data; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D050600:SNARE Proteins / Q000737:chemistry / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000737:chemistry / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D050600:SNARE Proteins; C116430:SRO7 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D006160:Guanosine Triphosphate; C064320:SEC4 protein, S cerevisiae; D020691:rab GTP-Binding Proteins