Vacuole acidification is required for trans-SNARE pairing, LMA1 release, and homotypic fusion.
Vacuole fusion occurs in three stages: priming, in which Sec18p mediates Sec17p release, LMA1 (low M(r) activity 1) relocation, and cis-SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complex disassembly; docking, mediated by Ypt7p and trans-SNARE association; and fusion of docked vacuoles. Ca(2+) and calmodulin regulate late stages of the reaction. We now show that the vacuole proton gradient, generated by the vacuolar proton ATPase, is needed for trans-SNARE complex formation during docking and hence for the subsequent LMA1 release. Though neither the vacuolar Pmc1p Ca(2+)-ATPase nor the Vcx1p Ca(2+)/H(+) exchanger are needed for the fusion reaction, they participate in Ca(2+) and Delta mu(H)(+) homeostasis. Fusion itself does not require the maintenance of trans-SNARE pairs.
Ungermann
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Department of Biochemistry, Dartmouth Medical School, 7200 Vail Building, Hanover, NH 03755-3844, USA.
Wickner
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Xu
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D002118:Calcium / Q000502:physiology; D019281:Dimerization; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D008561:Membrane Fusion; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D050600:SNARE Proteins; D014617:Vacuoles / Q000378:metabolism*; D033921:Vesicular Transport Proteins
D008565:Membrane Proteins; D050600:SNARE Proteins; D033921:Vesicular Transport Proteins; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium