Calcium drives fusion of SNARE-apposed bilayers.
N-ethylmalemide-sensitive factor attachment protein receptor (SNARE) has been proposed to play a critical role in the membrane fusion process. The SNARE complex was suggested to be the minimal fusion machinery. However, there is mounting evidence for a major role of calcium in membrane fusion. Hence, the role of calcium in SNARE-induced membrane fusion was the focus of this study. It revealed that recombinant v-SNARE and t-SNARE, reconstituted into separate liposomes, interact to bring lipid vesicles into close proximity, enabling calcium to drive fusion of opposing bilayers. Exposure to calcium triggered vesicle fusion at both, high potency and efficacy. The half-time for calcium-induced fusion of SNARE-reconstituted vesicles was determined to be approximately 10 s, which is two orders of magnitude faster than in its absence. Calcium acts downstream of SNAREs, since the presence of SNAREs in bilayers increases the potency of calcium-induced vesicle fusion, without significantly influencing its efficacy. Hence, this study suggests that in the physiological state in cells, both SNAREs and calcium operate as the minimal fusion machinery.
Jeremic
Aleksandar
A
Department of Physiology, Wayne State University School of Medicine, 5239 Scott Hall, 540 E. Canfield Avenue, Detroit, MI 48201, USA.
Kelly
Marie
M
Cho
Jin Ah
JA
Cho
Sang-Joon
SJ
Horber
J K Heinrich
JK
Jena
Bhanu P
BP
D002118:Calcium / Q000494:pharmacology*; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D004563:Electrochemistry; D005470:Fluorometry; D008051:Lipid Bilayers / Q000378:metabolism*; D008081:Liposomes / Q000378:metabolism; D008561:Membrane Fusion; D018625:Microscopy, Atomic Force; D050600:SNARE Proteins; D033921:Vesicular Transport Proteins / Q000378:metabolism*; D014961:X-Ray Diffraction
D008051:Lipid Bilayers; D008081:Liposomes; D050600:SNARE Proteins; D033921:Vesicular Transport Proteins; D002118:Calcium