The function of ENSG00000139641 (ESYT1, extended synaptotagmin 1) is as follows. Binds calcium (via the C2 domains) and translocates to sites of contact between the endoplasmic reticulum and the cell membrane in response to increased cytosolic calcium levels (PubMed:23791178, PubMed:24183667). Helps tether the endoplasmic reticulum to the cell membrane and promotes the formation of appositions between the endoplasmic reticulum and the cell membrane (PubMed:24183667). Acts as an inhibitor of ADGRD1 G protein-coupled receptor activity in absence of cytosolic calcium (PubMed:38758649). Binds glycerophospholipids in a barrel-like domain and may play a role in cellular lipid transport (By similarity). {ECO:0000250|UniProtKB:A0FGR8, ECO:0000269|PubMed:23791178, ECO:0000269|PubMed:24183667, ECO:0000269|PubMed:38758649}.