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synaptotagmin-like mitochondrial-lipid-binding protein (SMP) domain of the extended synaptotagmin (E-Syt) family The extended synaptotagmin (E-Syt) family includes a group of Ca2+-regulated intrinsic membrane proteins, such as E-Syt1, E-Syt2 and E-Syt3. They are composed of an N-terminal endoplasmic reticulum (ER)-membrane anchor, a central SMP-domain, and five (E-Syt1) or three C-terminal cytoplasmic C2-domains (E-Syt2 and E-Syt3). The ER-membrane anchor and C2 domains are required for tethering, while the SMP domain is a lipid-binding domain that links the ER with other lipid bilayer-membranes within the cell. This model corresponds to the SMP domain, which has a beta-barrel structure like protein modules in the tubular-lipid-binding (TULIP) superfamily. It dimerizes to form an approximately 90-Angstrom-long cylinder traversed by a channel lined entirely with hydrophobic residues. The following two C2 domains then form arched structures flexibly linked to the SMP domain.
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Jiyao W et al.(2023). "The conserved domain database in 2023.",