Molecular Basis of Proton Blockage in Aquaporins

Nilmadhab Chakrabarti, Emad Tajkhorshid, Benoît Roux, Régis Pomès

Research output: Contribution to journalArticlepeer-review

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.

Original languageEnglish (US)
Pages (from-to)65-74
Number of pages10
JournalStructure
Volume12
Issue number1
DOIs
StatePublished - Jan 2004

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology

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