aquaporin-4; AQP-4; WCH4; mercurial-insensitive water channel; MIWC (AQP4)

Function

• forms a water-specific channel
• osmoreceptor which regulates body water balance & mediates water flow within the central nervous system
• phosphorylation by PKC at Ser-180 reduces conductance by 50%
• phosphorylation by PKG at Ser-111 in response to glutamate increases conductance by 40% (putative)
• part of a complex containing MLC1, TRPV4, HEPACAM & ATP1B1

Structure

• homotetramer
• aquaporins contain two tandem repeats each containing 3 membrane-spanning domains & a pore-forming loop with the signature motif Asn-Pro-Ala (NPA)
• belongs to the MIP/aquaporin (TC 1.A.8) family

Compartment

• membrane, primarily on astrocyte end foot processes

Alternative splicing

named isoforms=2

Expression

• brain - muscle >> heart, kidney, lung, & trachea

Pathology

• autoantibody of Devic's disease (neuromyelitis optica)

Pharmacology

• inebilizumab-cdon (Uplizna) a CD19 monoclonal antibody is FDA-approved for treatment of neuromyelitis optica spectrum disorder (NMOSD) in adults with aquaporin-4 (AQP4) autoantibodies

Comparative biology

• contact of aquaporin-4 containing astrocyte end-feet with microvasculature of brain (mice)

More general terms

• transmembrane 6 protein
• aquaporin
• glycoprotein
• phosphoprotein

Database

• Entrez gene: http://www.ncbi.nlm.nih.gov/sites/entrez?db=gene&cmd=Retrieve&dopt=Graphics&list_uids=361
• Kegg: http://www.genome.jp/dbget-bin/www_bget?hsa:361
• OMIM: https://mirror.omim.org/entry/600308
• UniProt: http://www.uniprot.org/uniprot/P55087.html