Putative fusogenic activity of NSF is restricted to a lipid mixture whose coalescence is also triggered by other factors.
It has recently been reported that N-ethylmaleimide-sensitive fusion ATPase (NSF) can fuse protein-free liposomes containing substantial amounts of 1,2-dioleoylphosphatidylserine (DOPS) and 1, 2-dioleoyl-phosphatidyl-ethanolamine (DOPE) (Otter-Nilsson et al., 1999). The authors impart physiological significance to this observation and propose to re-conceptualize the general role of NSF in fusion processes. We can confirm that isolated NSF can fuse liposomes of the specified composition. However, this activity of NSF is resistant to inactivation by N-ethylmaleimide and does not depend on the presence of alpha-SNAP (soluble NSF-attachment protein). Moreover, under the same conditions, either alpha-SNAP, other proteins apparently unrelated to vesicular transport (glyceraldehyde-3-phosphate dehydrogenase or lactic dehydrogenase) or even 3 mM magnesium ions can also cause lipid mixing. In contrast, neither NSF nor the other proteins nor magnesium had any significant fusogenic activity with liposomes composed of a biologically occurring mixture of lipids. A straightforward explanation is that the lipid composition chosen as optimal for NSF favors non-specific fusion because it is physically unstable when formed into liposomes. A variety of minor perturbations could then trigger coalescence.
Brügger
B
B
Cellular Biochemistry and Biophysics Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10021, USA.
Nickel
W
W
Weber
T
T
Parlati
F
F
McNew
J A
JA
Rothman
J E
JE
Söllner
T
T
D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D005033:Ethylmaleimide / Q000494:pharmacology; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000378:metabolism; D006056:Golgi Apparatus / Q000737:chemistry; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D050356:Lipid Metabolism; D008081:Liposomes / Q000737:chemistry* / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D008561:Membrane Fusion / Q000187:drug effects; D008565:Membrane Proteins / Q000378:metabolism; D052066:N-Ethylmaleimide-Sensitive Proteins; D010713:Phosphatidylcholines / Q000378:metabolism; D010714:Phosphatidylethanolamines / Q000378:metabolism; D010718:Phosphatidylserines / Q000378:metabolism; D051381:Rats; D050600:SNARE Proteins; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D013816:Thermodynamics; D033921:Vesicular Transport Proteins
D002352:Carrier Proteins; D008081:Liposomes; D008565:Membrane Proteins; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010718:Phosphatidylserines; D050600:SNARE Proteins; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D033921:Vesicular Transport Proteins; C094877:dioleoyl phosphatidylethanolamine; C042511:1,2-dioleoylphosphatidylserine; D000255:Adenosine Triphosphate; D007770:L-Lactate Dehydrogenase; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D000251:Adenosine Triphosphatases; D052066:N-Ethylmaleimide-Sensitive Proteins; C498737:Nsf protein, rat; C017251:1,2-oleoylphosphatidylcholine; D008274:Magnesium; D005033:Ethylmaleimide