Proteins on exocytic vesicles mediate calcium-triggered fusion.
In many exocytic systems, micromolar concentrations of intracellular Ca2+ trigger fusion. We find that aggregates of secretory granules isolated from sea urchin eggs fuse together when perfused with greater than or equal to 10 microM free Ca2+. Mixing of membrane components was demonstrated by transfer of fluorescent lipophilic dye, and melding of granule contents was seen with differential interference microscopy. A technique based upon light scattering was developed to conveniently detect fusion. Two protein modifiers, trypsin and N-ethylmaleimide, inhibit granule-granule fusion at concentrations similar to those that inhibit granule-plasma membrane fusion. We suggest that molecular machinery sufficient for Ca(2+)-triggered fusion resides on secretory granules as purified and that at least some of these essential components are proteinaceous.
Vogel
S S
SS
Laboratory of Theoretical and Physical Biology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892.
Zimmerberg
J
J
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002232:Carbocyanines; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000502:physiology*; D005033:Ethylmaleimide / Q000494:pharmacology; D005089:Exocytosis / Q000502:physiology*; D005260:Female; D005456:Fluorescent Dyes; D007425:Intracellular Membranes / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008027:Light; D008561:Membrane Fusion / Q000187:drug effects*; D008856:Microscopy, Fluorescence; D010063:Ovum / Q000502:physiology*; D012542:Scattering, Radiation; D012617:Sea Urchins; D014357:Trypsin / Q000494:pharmacology; D014741:Video Recording
D002232:Carbocyanines; D005456:Fluorescent Dyes; C024286:3,3'-dioctadecylindocarbocyanine; D014357:Trypsin; D005033:Ethylmaleimide; D002118:Calcium