Exocytotic fusion is activated by Rab3a peptides.
Studies of intracellular traffic in yeast and mammalian systems have implicated members of the Rab family of small GTP-binding proteins as regulators of membrane fusion. We have used the patch clamp technique to measure exocytotic fusion events directly and investigate the role of GTP-binding proteins in regulating exocytosis in mast cells. Intracellular perfusion of mast cells with GTP-gamma S is sufficient to trigger complete exocytotic degranulation in the absence of other intracellular messengers. Here we show that GTP is a potent inhibitor of GTP-gamma S-induced degranulation, indicating that sustained activation of a GTP-binding protein is sufficient for membrane fusion. We have found that synthetic oligopeptides, corresponding to part of the effector domain of Rab3a, stimulate complete exocytotic degranulation, similar to that induced by GTP-gamma S. The response is selective for Rab3a sequence and is strictly dependent on Mg2+ and ATP. This suggests that sustained activation of a Rab3 protein causes exocytotic fusion. The peptide response can be accelerated by GDP-beta S, suggesting that Rab3a peptides compete with endogenous Rab3 proteins for a binding site on a target effector protein, which causes fusion on activation.
Oberhauser
A F
AF
Department of Physiology and Biophysics, Mayo Clinic, Rochester, Minnesota 55905.
Monck
J R
JR
Balch
W E
WE
Fernandez
J M
JM
D000595:Amino Acid Sequence; D000818:Animals; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D005260:Female; D019204:GTP-Binding Proteins / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D008407:Mast Cells / Q000166:cytology* / Q000187:drug effects; D008561:Membrane Fusion / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008954:Models, Biological; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000502:physiology*; D010446:Peptide Fragments / Q000502:physiology; D020692:rab3 GTP-Binding Proteins
D009419:Nerve Tissue Proteins; D010446:Peptide Fragments; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins; D020692:rab3 GTP-Binding Proteins