アクアポリン６の水・イオン透過機序

抄録

The aquaporins are a family of membrane proteins that are permeated by water but not by any ions. The structure of aquaporin-1 (AQP1) provides a uniquely selective mechanism for free permeation of water molecules through a channel and a mechanism for repelling hydronium ions. Ion permeability is not a general feature of aquaporins; we recently demonstrated, however, that aquaporin-6 (AQP6) functions not as a water channel but as an anion channel. Here we find that a single residue substitution at Asn-60 residue (N60G mutant) turns AQP6 into a constitutively active water channel without any ion conductance. Amino acid sequence alignment reveals that most aquaporins have a glycine residue at the corresponding residue of Asn-60 in AQP6: An atomic model of AQP1 structure indicates that the corresponding glycine residue is important for the protein folding. Asn-60 residue is, therefore, critical for anion permeation of AQP6, and that AQP6 might have quite distinct pore structure from other aquaporins. Structural comparison between AQP1 and AQP6 may explain a general mechanism for repelling any ions through aquaporins. [Jpn J Physiol 55 Suppl:S36 (2005)]