The Structural Basis for Activation of the Rab Ypt1p by the TRAPP Membrane-Tethering Complexes

Yiying Cai, Harvey F. Chin, Darina Lazarova, Shekar Menon, Chunmei Fu, Huaqing Cai, Anthony Sclafani, David W. Rodgers, Enrique M. De La Cruz, Susan Ferro-Novick, Karin M. Reinisch

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149 Scopus citations


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.

Original languageEnglish
Pages (from-to)1202-1213
Number of pages12
Issue number7
StatePublished - Jun 27 2008

Bibliographical note

Funding Information:
We are grateful to Yunrui Du for her gift of yeast genomic DNA, to Hong Zheng for help in overexpressing and purifying mutant TRAPPI subcomplexes, to Wei Wang for data used to assemble Figure 6 A, and to the staff at 24-ID at the Advanced Photon Source for help in data collection. We thank P. Novick for discussions regarding this manuscript. This work was supported by grants to K.M.R. from the Mathers Foundation and the NIH (GM080616) and to S.F.-N. from the Howard Hughes Medical Institute. E.M.D.L.C. is supported by grants from the NIH (GM071688), the NSF (MCB-0546353), and the American Heart Association (0655849T). D.W.R. is supported by grants from the NIH (NS38041, DA02243, RR020171). H.F.C. is supported by NIH predoctoral award 1F31DC009143-01. A.S. was supported by NIH predoctoral training grant T32-GM07223.



ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology (all)


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