title: The structural basis for activation of the Rab Ypt1p by the TRAPP membrane-tethering complexes.
abstract: The multimeric membrane-tethering complexes TRAPPI and TRAPPII share seven subunits, of which four (Bet3p, Bet5p, Trs23p, and Trs31p) are minimally needed to activate the Rab GTPase Ypt1p in an event preceding membrane fusion. Here, we present the structure of a heteropentameric TRAPPI assembly complexed with Ypt1p. We propose that TRAPPI facilitates nucleotide exchange primarily by stabilizing the nucleotide-binding pocket of Ypt1p in an open, solvent-accessible form. Bet3p, Bet5p, and Trs23p interact directly with Ypt1p to stabilize this form, while the C terminus of Bet3p invades the pocket to participate in its remodeling. The Trs31p subunit does not interact directly with the GTPase but allosterically regulates the TRAPPI interface with Ypt1p. Our findings imply that TRAPPII activates Ypt1p by an identical mechanism. This view of a multimeric membrane-tethering assembly complexed with a Rab provides a framework for understanding events preceding membrane fusion at the molecular level.
authors.affiliation: Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA.
authors.forename: Yiying
authors.initials: Y
authors.lastname: Cai
authors.forename: Harvey F
authors.initials: HF
authors.lastname: Chin
authors.forename: Darina
authors.initials: D
authors.lastname: Lazarova
authors.forename: Shekar
authors.initials: S
authors.lastname: Menon
authors.forename: Chunmei
authors.initials: C
authors.lastname: Fu
authors.forename: Huaqing
authors.initials: H
authors.lastname: Cai
authors.forename: Anthony
authors.initials: A
authors.lastname: Sclafani
authors.forename: David W
authors.initials: DW
authors.lastname: Rodgers
authors.forename: Enrique M
authors.initials: EM
authors.lastname: De La Cruz
authors.forename: Susan
authors.initials: S
authors.lastname: Ferro-Novick
authors.forename: Karin M
authors.initials: KM
authors.lastname: Reinisch
mesh_terms: D004721:Endoplasmic Reticulum / Q000378:metabolism; D004789:Enzyme Activation; D006056:Golgi Apparatus / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D025941:Protein Interaction Mapping; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; C406327:transport protein particle, TRAPP; C060755:YPT1 protein, S cerevisiae; D020691:rab GTP-Binding Proteins