The structural basis for activation of the Rab Ypt1p by the TRAPP membrane-tethering complexes.
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.
Cai
Yiying
Y
Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA.
Chin
Harvey F
HF
Lazarova
Darina
D
Menon
Shekar
S
Fu
Chunmei
C
Cai
Huaqing
H
Sclafani
Anthony
A
Rodgers
David W
DW
De La Cruz
Enrique M
EM
Ferro-Novick
Susan
S
Reinisch
Karin M
KM
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*
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