VAP-A (VAMP-associated protein A; also VAP-33) is a 33kD integral membrane protein that is ubiquitously expressed and found associated with multiple cellular organelles, including the Golgi, endosomes, tight junctions, and the cell membrane. VAP-A appears to be pleiotrophic in function, participating in synaptic vesicle fusion, maintenance of tight junction integrity, and the regulation of cholesterol synthesis. Human VAP-A is a type IV (small luminal domain) transmembrane protein 249aa in length. It is almost all cytoplasmic (aa1-227) with a one aa luminal fragment. The cytoplasmic region contains an MSP/motile sperm protein domain (aa14-131) plus a coiled-coil region (aa169-205). VAP-A homo- and hetero-dimerizes with VAP-B. It has multiple binding partners within the cell. There is one potential alternative start site at Met8, and an isoform that shows a 44aa insertion after Leu140. Over aa1-132, human VAP-A shares 97% aa identity with mouse VAP-A.