Yeast Sec1p functions before and after vesicle docking.
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.
Department of Pathology and Laboratory Medicine, University of Medicine and Dentistry, New Jersey-Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA.
Kristina
K
Hashizume
Yi-Shan
YS
Cheng
Jenna L
JL
Hutton
Chi-Hua
CH
Chiu
Chavela M
CM
Carr
D000595:Amino Acid Sequence; D000818:Animals; D022162:Cytoplasmic Vesicles / Q000378:metabolism*; D006801:Humans; D008561:Membrane Fusion / Q000502:physiology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D051938:Munc18 Proteins / Q000235:genetics / Q000378:metabolism*; D016296:Mutagenesis; D017434:Protein Structure, Tertiary; D050600:SNARE Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins / Q000378:metabolism
D051938:Munc18 Proteins; C497931:SEC1 protein, S cerevisiae; D050600:SNARE Proteins; D029701:Saccharomyces cerevisiae Proteins; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins