Trans-complex formation by proteolipid channels in the terminal phase of membrane fusion.
SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) and Rab-GTPases, together with their cofactors, mediate the attachment step in the membrane fusion of vesicles. But how bilayer mixing--the subsequent core process of fusion--is catalysed remains unclear. Ca2+/calmodulin controls this terminal process in many intracellular fusion events. Here we identify V0, the membrane-integral sector of the vacuolar H+-ATPase, as a target of calmodulin on yeast vacuoles. Between docking and bilayer fusion, V0 sectors from opposing membranes form complexes. V0 trans-complex formation occurs downstream from trans-SNARE pairing, and depends on both the Rab-GTPase Ypt7 and calmodulin. The maintenance of existing complexes and completion of fusion are independent of trans-SNARE pairs. Reconstituted proteolipids form sealed channels, which can expand to form aqueous pores in a Ca2+/calmodulin-dependent fashion. V0 trans-complexes may therefore form a continuous, proteolipid-lined channel at the fusion site. We propose that radial expansion of such a protein pore may be a mechanism for intracellular membrane fusion.
Peters
C
C
Friedrich-Miescher-Laboratorium der Max-Planck-Gesellschaft, Tübingen, Germany.
Bayer
M J
MJ
Bühler
S
S
Andersen
J S
JS
Mann
M
M
Mayer
A
A
D002147:Calmodulin / Q000378:metabolism*; D002462:Cell Membrane; D008561:Membrane Fusion; D008565:Membrane Proteins / Q000378:metabolism*; D011485:Protein Binding; D011510:Proteolipids / Q000378:metabolism*; D017494:Proton Pumps / Q000378:metabolism*; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D050600:SNARE Proteins; D033921:Vesicular Transport Proteins; D015003:Yeasts
D002147:Calmodulin; D008565:Membrane Proteins; D011510:Proteolipids; D017494:Proton Pumps; D050600:SNARE Proteins; D033921:Vesicular Transport Proteins; D006180:Proton-Translocating ATPases