VAP-B (vesicle-associated membrane protein (VAMP)-associated protein B) is a ubiquitously expressed type IV transmembrane protein belonging to the VAP family. It is found in ER, Golgi and other membranes as a homodimer or a heterodimer with VAP-A. VAPs recruit FFAT proteins that mediate many of their effects on regulation of membrane transport, phospholipid biosynthesis, microtubule organization, and the unfolded protein response. VAPs also interact with some SNARE and viral proteins, notably hepatitis C virus (HCV), which requires VAB-B for its propagation. The P56S polymorphism of VAP-B is found in amylotrophic lateral sclerosis and causes formation of intracellular aggregates and increased ER-stress-induced death of motor neurons. It can also promote cleavage and secretion of soluble VAP-B, which can then function as a ligand for EPH receptors.