Protonation equilibria and pore-opening structure of the dual-histidine influenza B virus M2 transmembrane proton channel from solid-state NMR

Jonathan K. Williams, Alexander A. Shcherbakov, Jun Wang, Mei Hong

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Abstract

The influenza A and B viruses are the primary cause of seasonal flu epidemics. Common to both viruses is the M2 protein, a homotetrameric transmembrane proton channel that acidifies the virion after endocytosis. Although influenza A M2 (AM2) and B M2 (BM2) are functional analogs, they have little sequence homology, except for a conserved HXXXW motif, which is responsible for proton selectivity and channel gating. Importantly, BM2 contains a second titratable histidine, His-27, in the tetrameric transmembrane domain that forms a reverse WXXXH motif with the gating tryptophan. To understand how His-27 affects the proton conduction property of BM2, we have used solid-state NMR to characterize the pH-dependent structure and dynamics of His-27. In cholesterol-containing lipid membranes mimicking the virus envelope, 15N NMR spectra show that the His-27 tetrad protonates with higher pKa values than His-19, indicating that the solvent-accessible His-27 facilitates proton conduction of the channel by increasing the proton dissociation rates of His-19. AM2 is inhibited by the amantadine class of antiviral drugs, whereas BM2 has no known inhibitors. We measured the N-terminal interhelical separation of the BM2 channel using fluorinated Phe-5. The interhelical 19F-19F distances show a bimodal distribution of a short distance of 7 A˚ and a long distance of 15–20 A˚, indicating that the phenylene rings do not block small-molecule entry into the channel pore. These results give insights into the lack of amantadine inhibition of BM2 and reveal structural diversities in this family of viral proton channels.

Original languageEnglish (US)
Pages (from-to)17876-17884
Number of pages9
JournalJournal of Biological Chemistry
Volume292
Issue number43
DOIs
StatePublished - Oct 27 2017

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ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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