Binds to OSBPL3, which mediates recruitment of VAPA to plasma membrane sites. The ORP3-VAPA complex stimulates RRAS signaling which in turn attenuates integrin beta-1 (ITGB1) activation at the cell surface. With OSBPL3, may regulate ER morphology. May play a role in vesicle trafficking. Homodimer, and heterodimer with VAPB. Interacts with VAMP1, VAMP2, STX1A, BET1, SEC22C and with the C-terminal domain of OCLN. Interacts with OSBPL1A. Interacts (via MSP domain) with ZFYVE27; may retain ZFYVE27 in the endoplasmic reticulum and regulate its function in cell projections formation. Interacts with OSBP. Interacts (via C-terminus) with RSAD2/viperin (via C-terminus). Interacts with OSBPL3 (phosphorylated form). Interacts with STARD3 (via FFAT motif). Interacts with STARD3NL (via FFAT motif). Interacts with CERT1 (By similarity). Interacts with PLEKHA3 and SACM1L to form a ternary complex (By similarity). Interacts with VPS13A (via FFAT motif) (By similarity). Present in the plasma membrane and in intracellular vesicles, together with SNARE proteins. May also associate with the cytoskeleton. Colocalizes with OCLN at the tight junction in polarized epithelial cells. Belongs to the VAMP-associated protein (VAP) (TC 9.B.17) family.