Functional and biochemical analysis of the C2 domains of synaptotagmin IV.
Synaptotagmins (Syts) are a family of vesicle proteins that have been implicated in both regulated neurosecretion and general membrane trafficking. Calcium-dependent interactions mediated through their C2 domains are proposed to contribute to the mechanism by which Syts trigger calcium-dependent neurotransmitter release. Syt IV is a novel member of the Syt family that is induced by cell depolarization and has a rapid rate of synthesis and a short half-life. Moreover, the C2A domain of Syt IV does not bind calcium. We have examined the biochemical and functional properties of the C2 domains of Syt IV. Consistent with its non-calcium binding properties, the C2A domain of Syt IV binds syntaxin isoforms in a calcium-independent manner. In neuroendocrine pheochromocytoma (PC12) cells, Syt IV colocalizes with Syt I in the tips of the neurites. Microinjection of the C2A domain reveals that calcium-independent interactions mediated through this domain of Syt IV inhibit calcium-mediated neurotransmitter release from PC12 cells. Conversely, the C2B domain of Syt IV contains calcium binding properties, which permit homo-oligomerization as well as hetero-oligomerization with Syt I. Our observation that different combinatorial interactions exist between Syt and syntaxin isoforms, coupled with the calcium stimulated hetero-oligomerization of Syt isoforms, suggests that the secretory machinery contains a vast repertoire of biochemical properties for sensing calcium and regulating neurotransmitter release accordingly.
Thomas
D M
DM
Department of Biological Sciences, Wayne State University, Detroit, Michigan 48202, USA.
Ferguson
G D
GD
Herschman
H R
HR
Elferink
L A
LA
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D008845:Microinjections; D009154:Mutation; D009414:Nerve Growth Factors / Q000494:pharmacology; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D016501:Neurites / Q000378:metabolism; D016716:PC12 Cells / Q000187:drug effects / Q000378:metabolism; D050765:Qa-SNARE Proteins; D051381:Rats; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D050857:Synaptotagmins
D002135:Calcium-Binding Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins; D050765:Qa-SNARE Proteins; D011994:Recombinant Proteins; C494294:Syt4 protein, rat; D050857:Synaptotagmins; D002118:Calcium