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].

1: Structure of a lipid-bound extended synaptotagmin indicates a role in lipid transfer. Schauder CM, Wu X, Saheki Y, Narayanaswamy P, Torta F, Wenk MR, De Camilli P, Reinisch KM; Nature. 2014;510:552-555. PMID:24847877