Calcium-triggered fusion of exocytotic granules requires proteins in only one membrane.
We studied calcium-triggered fusion of sea urchin egg secretory granules to test whether membrane bound fusion proteins are required in both fusing membranes. Using both light scattering assays and video microscopy, we found that native granules fused to granules that had been inactivated with either trypsin or N-ethylmaleimide. Granules also fused with liposomes prepared from lipids extracted from egg cortices and with liposomes made from synthetic phospholipids and cholesterol. Granule-liposome fusion required no cytoplasmic proteins and was inhibited by N-ethylmaleimide. Thus, membrane fusion of exocytotic granules can be promoted by proteins residing on only one of the two membranes.
Vogel
S S
SS
Laboratory of Theoretical and Physical Biology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892.
Chernomordik
L V
LV
Zimmerberg
J
J
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology*; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D005033:Ethylmaleimide / Q000494:pharmacology; D005089:Exocytosis; D005260:Female; D008027:Light; D008081:Liposomes; D008561:Membrane Fusion / Q000187:drug effects / Q000502:physiology*; D008565:Membrane Proteins / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D010063:Ovum / Q000502:physiology*; D012235:Rhodamines; D012542:Scattering, Radiation; D012617:Sea Urchins; D014357:Trypsin / Q000494:pharmacology
D008081:Liposomes; D008565:Membrane Proteins; D012235:Rhodamines; D014357:Trypsin; D005033:Ethylmaleimide; D002118:Calcium