PMID:14725766

Citation	Chakrabarti, N, Tajkhorshid, E, Roux, B and Pomès, R (2004) Molecular basis of proton blockage in aquaporins. Structure 12:65-74
Abstract	Water transport channels in membrane proteins of the aquaporin superfamily are impermeable to ions, including H+ and OH-. We examine the molecular basis for the blockage of proton translocation through the single-file water chain in the pore of a bacterial aquaporin, GlpF. We compute the reversible thermodynamic work for the two complementary steps of the Grotthuss "hop-and-turn" relay mechanism: consecutive transfers of H+ along the hydrogen-bonded chain (hop) and conformational reorganization of the chain (turn). In the absence of H+, the strong preference for the bipolar orientation of water around the two Asn-Pro-Ala (NPA) motifs lining the pore over both unidirectional polarization states of the chain precludes the reorganization of the hydrogen-bonded network. Inversely, translocation of an excess proton in either direction is opposed by a free-energy barrier centered at the NPA region. Both hop and turn steps of proton translocation are opposed by the electrostatic field of the channel.
Links	PubMed
Keywords	Aquaporins/chemistry; Aquaporins/genetics; Biological Transport/physiology; Computer Simulation; Hydrogen/chemistry; Hydrogen Bonding; Ion Channels/chemistry; Ion Channels/genetics; Models, Molecular; Oxygen/chemistry; Protons; Static Electricity; Structure-Activity Relationship; Water/chemistry
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