Tethering protein that creates contact site between the endoplasmic reticulum and late endosomes: localizes to late endosome membranes and contacts the endoplasmic reticulum via interaction with VAPA and VAPB (PubMed:24105263). Homodimer (PubMed:16709157). Interacts (via the MENTAL domain) with STARD3NL (PubMed:16709157). Interacts (via FFAT motif) with VAPA. Interacts (via FFAT motif) with VAPB (PubMed:24105263). Interacts (via FFAT motif) with MOSPD2 (via MSP domain) (PubMed:29858488). Localizes to contact sites between the endoplasmic reticulum and late endosomes: associates with the endoplasmic reticulum membrane via interaction with VAPA, VAPB or MOSPD2. The FFAT motif mediates interaction with VAPA, VAPB and MOSPD2. The MENTAL domain anchors the protein in endosome membranes and exposes the START domain in the cytosol (By similarity). It binds cholesterol and mediates homotypic as well as heterotypic interactions between STARD3 and STARD3NL (PubMed:15718238, PubMed:16709157). Belongs to the STARD3 family.