Different domains of synaptotagmin control the choice between kiss-and-run and full fusion.
Exocytosis-the release of the contents of a vesicle--proceeds by two mechanisms. Full fusion occurs when the vesicle and plasma membranes merge. Alternatively, in what is termed kiss-and-run, vesicles can release transmitter during transient contacts with the plasma membrane. Little is known at the molecular level about how the choice between these two pathways is regulated. Here we report amperometric recordings of catecholamine efflux through individual fusion pores. Transfection with synaptotagmin (Syt) IV increased the frequency and duration of kiss-and-run events, but left their amplitude unchanged. Endogenous Syt IV, induced by forskolin treatment, had a similar effect. Full fusion was inhibited by mutation of a Ca2+ ligand in the C2A domain of Syt I; kiss-and-run was inhibited by mutation of a homologous Ca2+ ligand in the C2B domain of Syt IV. The Ca2+ sensitivity for full fusion was 5-fold higher with Syt I than Syt IV, but for kiss-and-run the Ca2+ sensitivities differed by a factor of only two. Syt thus regulates the choice between full fusion and kiss-and-run, with Ca2+ binding to the C2A and C2B domains playing an important role in this choice.
Wang
Chih-Tien
CT
Department of Physiology, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Lu
Juu-Chin
JC
Bai
Jihong
J
Chang
Payne Y
PY
Martin
Thomas F J
TF
Chapman
Edwin R
ER
Jackson
Meyer B
MB
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins; D002462:Cell Membrane / Q000378:metabolism*; D002463:Cell Membrane Permeability; D005576:Colforsin / Q000494:pharmacology; D005089:Exocytosis; D008024:Ligands; D008561:Membrane Fusion; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016716:PC12 Cells; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051381:Rats; D050857:Synaptotagmins
D002135:Calcium-Binding Proteins; D008024:Ligands; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D050857:Synaptotagmins; D005576:Colforsin; D002118:Calcium