Molecular dynamics simulations of the transport of reactive oxygen species by mammalian and plant aquaporins

• Both mammalian and plant aquaporins may act as H2O2 channels.
• Solution-to-pore transfer free energies were low for HO and HO2 radicals.
• HO might enter the pore and oxidize amino acids responsible for channel selectivity.
• O2− radicals could in principle diffuse through aquaporins in the form of HO2.
• Oxidation of disulfide bonds in the plant aquaporin did not lead to oxidative gating.

BackgroundAquaporins are responsible for water transport across lipid membranes. They are also able to transport reactive oxygen species, playing an important role in redox signaling. Certain plant aquaporins have even the ability to be regulated by oxidative stress. However, the underlying mechanisms are still not fully understood.MethodsHere, molecular dynamics simulations were employed to determine the activation free energies related to the transport of reactive oxygen species through both mammalian and plant aquaporin models.Results and conclusionsBoth aquaporins may transport hydrogen peroxide (H2O2) and the protonated form of superoxide radicals (HO2). The solution-to-pore transfer free energies were low for small oxy-radicals, suggesting that even highly reactive hydroxyl radicals (HO) might have access to the pore interior and oxidize amino acids responsible for channel selectivity. In the plant aquaporin, no significant change in water permeability was observed upon oxidation of the solvent-exposed disulfide bonds at the extracellular region. During the simulated time scale, the existence of a direct oxidative gating mechanism involving these disulfide bonds could not be demonstrated.General significanceSimulation results may improve the understanding of redox signaling mechanisms and help in the interpretation of protein oxidative labeling experiments.

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