Sterol-binding protein that mediates cholesterol transport from the endoplasmic reticulum to endosomes. The sterol transport mechanism is triggered by phosphorylation of FFAT motif that leads to membrane tethering between the endoplasmic reticulum and late endosomes via interaction with VAPA and VAPB. Acts as a lipid transfer protein that redirects sterol to the endosome at the expense of the cell membrane and favors membrane formation inside endosomes. May also mediate cholesterol transport between other membranes, such as mitochondria membrane or cell membrane. However, such results need additional experimental evidences; probably mainly mediates cholesterol transport from the endoplasmic reticulum to endosomes. Does not activate transcriptional cholesterol sensing. Able to bind other lipids, such as lutein, a xanthophyll carotenoids that form the macular pigment of the retina (By similarity). Able to bind other lipids, such as lutein, a xanthophyll carotenoids that form the macular pigment of the retina .
Subcellular locations: Late endosome membrane
Localizes to contact sites between the endoplasmic reticulum and late endosomes: associates with the endoplasmic reticulum membrane via interaction with VAPA, VAPB or MOSPD2.
Present in retina. Localizes to all neurons of macular retina and especially cone inner segments and axons (at protein level).