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Description

Aquaporin-4 (UniProt: P55087, also known as AQP-4, Mercurial-insensitive water channel, MIWC, WCH4) is encoded by the AGP4 gene (Gene ID: 361) in human. Aquaporin-4 is a multi-pass membrane protein that forms a water-specific channel and serves as an osmoreceptor that regulates body water balance and mediates water flow within the central nervous system. Its extracellular domains are localized to amino acids 58-64, 137-155, and 206-231), its transmembrane domains are in amino acids 37-57, 65-85, 116-136, 156-176, 185-205, and 232-252), and the cytoplasmic domain is in amino acids 1-36, 86-115, 177-184, and 253-323). Aquaporin-4 is largely expressed in the brain and the skeletal muscle and at lower levels in heart, kidney, and lung tissue. Phosphorylation of Aquaporin-4 at Serine 180 by protein kinase C is shown to reduce conductance by about 50%, whereas phosphorylation at Serine 111 by protein kinase G in response to glutamate can increase conductance by about 40%. Two isoforms of Aquaporin-4 have been described that are produced by alternative splicing. Antibodies to Aquaporin-4 can serve as useful serum markers to distinguishing neuromyelitis optica (NMO) from multiple sclerosis. Clone mECD is shown to induce clustering and internalization of Aquporin-4 and cause its redistribution, which is also observed with NMO-IgG. Exposure to mECD antibody is also shown to cause coaggregation of astrocytic CD28B and Aquaporin-4. (Ref.: Hinson, SR et al. (2017). Proc. Natl.Acad. Sci. USA 114(21), 5491-5496).