vesicle-associated membrane protein-associated protein B/C (VAPB) is presents in mitochondria-associated membranes that are endoplasmic reticulum membrane regions closely apposed to the outer mitochondrial membrane. It can form homodimer, and heterodimer with VAPA. It also interacts with VAMP1, VAMP2, HCV NS5A, NS5B, ZFYVE27 and RMDN3. VAPB participates in the endoplasmic reticulum unfolded protein response (UPR) by inducing ERN1/IRE1 activity. It is involved in cellular calcium homeostasis regulation.