Critical Role of Water Molecules in Proton Translocation by the Membrane-Bound Transhydrogenase

Pius S. Padayatti, Josephine H. Leung, Paween Mahinthichaichan, Emad Tajkhorshid, Andrii Ishchenko, Vadim Cherezov, S. Michael Soltis, J. Baz Jackson, C. David Stout, Robert B. Gennis, Qinghai Zhang

Research output: Contribution to journalArticlepeer-review

Abstract

The nicotinamide nucleotide transhydrogenase (TH) is an integral membrane enzyme that uses the proton-motive force to drive hydride transfer from NADH to NADP+ in bacteria and eukaryotes. Here we solved a 2.2-Å crystal structure of the TH transmembrane domain (Thermus thermophilus) at pH 6.5. This structure exhibits conformational changes of helix positions from a previous structure solved at pH 8.5, and reveals internal water molecules interacting with residues implicated in proton translocation. Together with molecular dynamics simulations, we show that transient water flows across a narrow pore and a hydrophobic “dry” region in the middle of the membrane channel, with key residues His42α2 (chain A) being protonated and Thr214β (chain B) displaying a conformational change, respectively, to gate the channel access to both cytoplasmic and periplasmic chambers. Mutation of Thr214β to Ala deactivated the enzyme. These data provide new insights into the gating mechanism of proton translocation in TH.

Original languageEnglish (US)
Pages (from-to)1111-1119.e3
JournalStructure
Volume25
Issue number7
DOIs
StatePublished - Jul 5 2017

Keywords

  • X-ray crystallography
  • membrane protein
  • molecular dynamics simulations
  • proton channel
  • transhydrogenase

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology

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