Tethers the endoplasmic reticulum to the cell membrane and promotes the formation of appositions between the endoplasmic reticulum and the cell membrane. Binds glycerophospholipids in a barrel-like domain and may play a role in cellular lipid transport (By similarity). Localizes to endoplasmic reticulum-plasma membrane contact sites (EPCS). Recruited to the cell membrane via the third C2 domain (By similarity). The SMP-LTD domain is a barrel-like domain that binds glycerophospholipids in its interior (By similarity). Belongs to the extended synaptotagmin family.