Sec18p and Vam7p remodel trans-SNARE complexes to permit a lipid-anchored R-SNARE to support yeast vacuole fusion.
Intracellular membrane fusion requires SNARE proteins in a trans-complex, anchored to apposed membranes. Proteoliposome studies have suggested that SNAREs drive fusion by stressing the lipid bilayer via their transmembrane domains (TMDs), and that SNARE complexes require a TMD in each docked membrane to promote fusion. Yeast vacuole fusion is believed to require three Q-SNAREs from one vacuole and the R-SNARE Nyv1p from its fusion partner. In accord with this model, we find that fusion is abolished when the TMD of Nyv1p is replaced by lipid anchors, even though lipid-anchored Nyv1p assembles into trans-SNARE complexes. However, normal fusion is restored by the addition of both Sec18p and the soluble SNARE Vam7p. In restoring fusion, Sec18p promotes the disassembly of trans-SNARE complexes, and Vam7p enhances their assembly. Thus, either the TMD of this R-SNARE is not essential for fusion, and TMD-mediated membrane stress is not the only mode of trans-SNARE complex action, or these SNAREs have more flexibility than heretofore appreciated to form alternate functional complexes that violate the 3Q:1R rule.
Jun
Youngsoo
Y
Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755-3844, USA.
Xu
Hao
H
Thorngren
Naomi
N
Wickner
William
W
D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008561:Membrane Fusion / Q000502:physiology*; D008563:Membrane Lipids / Q000737:chemistry*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D046912:Multiprotein Complexes / Q000378:metabolism; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D050765:Qa-SNARE Proteins / Q000235:genetics / Q000378:metabolism; D050767:Qc-SNARE Proteins / Q000235:genetics / Q000378:metabolism*; D050683:R-SNARE Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D050600:SNARE Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D050825:Synaptosomal-Associated Protein 25; D014617:Vacuoles / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism*
D008051:Lipid Bilayers; D008563:Membrane Lipids; D008565:Membrane Proteins; D046912:Multiprotein Complexes; C500806:Nyv1 protein, S cerevisiae; D050765:Qa-SNARE Proteins; D050767:Qc-SNARE Proteins; D050683:R-SNARE Proteins; D011993:Recombinant Fusion Proteins; D050600:SNARE Proteins; D029701:Saccharomyces cerevisiae Proteins; D050825:Synaptosomal-Associated Protein 25; C107706:VAM3 protein, S cerevisiae; C494205:VAM7 protein, S cerevisiae; D033921:Vesicular Transport Proteins; D000251:Adenosine Triphosphatases; C064404:SEC18 protein, S cerevisiae