Multiple N-ethylmaleimide-sensitive components are required for endosomal vesicle fusion.
This report examines the inhibition of endosomal vesicle fusion by the alkylating agent N-ethylmaleimide (NEM). The concentration of NEM required to inhibit vesicle fusion depended upon whether membrane and cytosolic fractions were treated separately or together, enabling the resolution of at least two components to the inhibition. The first component is inactivated at low levels of NEM when cytosolic and membrane fractions are treated together. On the contrary, inhibition of the second component required higher levels of NEM but was achieved by treating cytosol and membranes separately. Reconstitution studies indicated that both components were cytosolic and that neither corresponded to the ubiquitous NEM-sensitive fusion protein (NSF). The role of NSF in this fusion reaction was further examined using salt-washed membranes depleted of NSF protein. Under these conditions the fusion reaction was fully dependent upon added NSF whose activity, in this context, was sensitive to NEM treatment. From these data we conclude that NSF activity during endosomal vesicle fusion can be dissected into several steps, only a subset of which (perhaps attachment of NSF to the membrane) are sensitive to NEM. Fusion between salt-washed endosomal membranes was also dependent on soluble NSF attachment proteins.
Rodriguez
L
L
Division of Biochemistry, School of Biological Sciences, University of Manchester, England.
Stirling
C J
CJ
Woodman
P G
PG
D001692:Biological Transport; D002352:Carrier Proteins / Q000502:physiology*; D002462:Cell Membrane / Q000187:drug effects; D003600:Cytosol / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D011992:Endosomes / Q000187:drug effects*; D005033:Ethylmaleimide / Q000494:pharmacology*; D006056:Golgi Apparatus / Q000378:metabolism / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D008561:Membrane Fusion / Q000187:drug effects*; D008565:Membrane Proteins / Q000502:physiology*; D052066:N-Ethylmaleimide-Sensitive Proteins; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D033921:Vesicular Transport Proteins
D002352:Carrier Proteins; D008565:Membrane Proteins; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D033921:Vesicular Transport Proteins; D052066:N-Ethylmaleimide-Sensitive Proteins; D005033:Ethylmaleimide