AQP9
Domain
Aquaporins contain two tandem repeats each containing three membrane-spanning domains and a pore-forming loop with the signature motif Asn-Pro-Ala (NPA).
Function
Aquaglyceroporins form homotetrameric transmembrane channels, with each monomer independently mediating glycerol and water transport across the plasma membrane along their osmotic gradient (PubMed:10564231, PubMed:30420639, PubMed:35054513, PubMed:9514918). AQP9 is the primary route for glycerol uptake in hepatocytes, supporting hepatic gluconeogenesis (By similarity). It exhibits broad specificity and may transport various small, non-charged solutes, including carbamides, polyols, purines, and pyrimidines (PubMed:10564231). AQP9 may also facilitate hepatic urea extrusion (PubMed:10564231, PubMed:9514918). Due to its permeability to lactate, AQP9 might participate in the astrocyte-to-neuron lactate shuttle, supplying neurons with energy (PubMed:10564231, PubMed:35054513). Additionally, AQP9 is permeable to arsenite, contributing to arsenic excretion by the liver and providing partial protection against arsenic toxicity (PubMed:10564231). It is also permeable to H2O2 in vivo (PubMed:26837049). Could also be permeable to ammonium (By similarity).
Sequence Similarities
Belongs to the MIP/aquaporin (TC 1.A.8) family.
Tissue Specificity
Highly expressed in peripheral leukocytes. Also expressed in liver, lung, and spleen.
Cellular localization
- Cell membrane
- Multi-pass membrane protein
- Basolateral cell membrane
- Multi-pass membrane protein
- Functions at the hepatocyte basolateral membrane.
Alternative names
SSC1, AQP9, Aquaporin-9, AQP-9, Aquaglyceroporin-9, Small solute channel 1