InterPro domain: IPR039010

SMP is a proposed lipid-binding module, ie a synaptotagmin-like mitochondrial-lipid-binding domain found in eukaryotes. The SMP domain has a beta-barrel structure like protein modules in the tubular-lipid-binding (TULIP) superfamily. It dimerises 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. The SMP domain is a lipid-binding domain that links the ER with other lipid bilayer-membranes within the cell [ 1 ].

This entry represents the SMP domain found in plant synaptotagmins [ 2 ] and extended synaptotagmins from metazoa. The extended synaptotagmins transport glycerolipids between the two bilayers via their lipid-harboring SMP domains and Ca2 + regulates their membrane tethering and lipid transport function [ 3 ].

1. Structure of a lipid-bound extended synaptotagmin indicates a role in lipid transfer. Nature 510, 552-5
2. Arabidopsis SYT1 maintains stability of cortical endoplasmic reticulum networks and VAP27-1-enriched endoplasmic reticulum-plasma membrane contact sites. J. Exp. Bot. 67, 6161-6171
3. The Extended-Synaptotagmins. Biochim. Biophys. Acta 1864, 1490-1493