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Synaptotagmin 1 (or synaptotagmin) is a Ca2+ sensor in the membrane of the pre-synaptic axon terminal, coded by gene SYT1 (previously SYT) at 12q21.2 (MIM:185605).〔http://videocast.nih.gov/summary.asp?Live=11162&bhsw=1366&bhqs=1〕 Synaptotagmins (SYTs) constitute a family of membrane-trafficking proteins that are characterized by an N-terminal transmembrane region (TMR), a variable linker, and two C-terminal C2 domains - C2A and C2B. There are 15 members in the mammalian synaptotagmin family. There are several C2-domain containing protein families that are related to synaptotagmins, including transmembrane (Ferlins, E-Syts, and MCTPs) and soluble (RIMs, Munc13s, synaptotagmin-related proteins and B/K) proteins. ==Functions== Based on their brain/endocrine distribution and biochemical properties, in particular C2 domains of certain synaptotagmins bound to calcium, synaptotagmins were proposed to function as calcium sensors in the regulation of neurotransmitter release and hormone secretion. Although synaptotagmins share a similar domain structure and a high degree of homology in the C2 domains, not all synaptotagmins bind to calcium. In fact, only eight out of the fifteen synaptotagmins are capable of calcium binding. The calcium binding synaptotagmins include synaptotagmins 1, 2, 3, 5, 6, 7, 9, and 10. The remaining seven synaptotagmins do not bind to calcium due to the lack of calcium coordinating residues or spatial orientation of the acidic residues (see the section on C2 domains for details). Calcium-binding synaptotagmins act as Ca2+ sensors and are involved in both: # early synaptic vesicle docking to the presynaptic membrane via interaction with β-neurexin〔 〕 or SNAP-25〔 〕 # late steps of Ca2+-evoked synaptic vesicle fusion with the presynaptic membrane.〔 〕〔 〕〔 〕 It was recently shown that synaptotagmin 1 can displace complexin from the SNARE complex in the presence of calcium. This is thought to be one of the last steps in exocytosis.〔 〕 Calcium-bound synaptotagmin binding to the SNARE complex, causes the fusion clamp effect of complexin to be released, allowing vesicle fusion to occur and exocytosis to proceed. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Synaptotagmin 1」の詳細全文を読む スポンサード リンク
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