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Originally published as MBC in Press, 10.1091/mbc.E09-02-0172 on September 23, 2009

Vol. 20, Issue 22, 4673-4685, November 15, 2009

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Yeast Sec1p Functions before and after Vesicle Docking

Kristina Hashizume*, Yi-Shan Cheng*, Jenna L. Hutton{dagger}, Chi-hua Chiu{ddagger}, and Chavela M. Carr*,§

Departments of *Pathology and Laboratory Medicine and {dagger}Molecular Genetics and Microbiology, University of Medicine and Dentistry, New Jersey-Robert Wood Johnson Medical School, Piscataway, NJ 08854; and {ddagger}Department of Genetics, Center for Human Evolutionary Studies, Rutgers University, Piscataway, NJ 08854

Submitted March 2, 2009; Revised August 17, 2009; Accepted September 14, 2009
Monitoring Editor: Patrick J. Brennwald

InCytes from MBC

Sec1/Munc18 (SM) proteins bind cognate soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes and stimulate vesicle membrane fusion. Before fusion, vesicles are docked to specific target membranes. Regulation of vesicle docking is attributed to some but not all SM proteins, suggesting specialization of this earlier function. Yeast Sec1p seems to function only after vesicles are docked and SNARE complexes are assembled. Here, we show that yeast Sec1p is required before and after SNARE complex assembly, in support of general requirements for SM proteins in both vesicle docking and fusion. Two classes of sec1 mutants were isolated. Class A mutants are tightly blocked in cell growth and secretion at a step before SNARE complex assembly. Class B mutants have a SNARE complex binding defect, with a range in severity of cell growth and secretion defects. Mapping the mutations onto an SM protein structure implicates a peripheral bundle of helices for the early, docking function and a deep groove, opposite the syntaxin-binding cleft on nSec1/Munc-18, for the interaction between Sec1p and the exocytic SNARE complex.

This article was published online ahead of print in MBC in Press (http://www.molbiolcell.org/cgi/doi/10.1091/mbc.E09-02-0172) on September 23, 2009.

§Present address: Department of Biochemistry and Biophysics, 300 Olsen Blvd., Texas A&M University, College Station, TX 77843.

Address correspondence to: Chavela M. Carr (chave{at}tamu.edu)

Abbreviations used: IP, immunoprecipitation; SM, Sec1/Munc18; SNARE, soluble N-ethylmaleimide-sensitive factor attachment protein receptor.


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