H95 Is a pH-Dependent Gate in Aquaporin 4

Aquaporin 4 (AQP4) is a transmembrane protein from the aquaporin family and is the predominant water channel in the mammalian brain. The regulation of permeability of this protein could be of potential therapeutic use to treat various forms of damage to the nervous tissue. In this work, based on data obtained from in silico and in vitro studies, a pH sensitivity that regulates the osmotic water permeability of AQP4 is demonstrated. The results indicate that AQP4 has increased water permeability at conditions of low pH in atomistic computer simulations and experiments carried out on Xenopus oocytes expressing AQP4. With molecular dynamics simulations, this effect was traced to a histidine residue (H95) located in the cytoplasmic lumen of AQP4. A mutant form of AQP4, in which H95 was replaced with an alanine (H95A), loses sensitivity to cytoplasmic pH changes in in vitro osmotic water permeability, thereby substantiating the in silico work. •AQP4 is studied using combined molecular dynamics and in vitro studies•Regulation of the permeability of AQP4 is shown to be pH sensitive•The protonation state of H95 is shown to influence the permeability of the protein•The H95A mutant loses pH sensitivity Kaptan et al. demonstrate that AQP4 permeability is regulated via a conserved histidine residue H95. The regulation is dependent on the protonation state of the residue and is sensitive to cytoplasmic pH conditions. A mutation of H95 to alanine abolishes the pH sensitivity of AQP4.