Identification of the functional core of the influenza A virus A/M2 proton-selective ion channel

Proc Natl Acad Sci U S A. 2009 Jul 28;106(30):12283-8. doi: 10.1073/pnas.0905726106. Epub 2009 Jul 9.


The influenza A virus M2 protein (A/M2) is a homotetrameric pH-activated proton transporter/channel that mediates acidification of the interior of endosomally encapsulated virus. This 97-residue protein has a single transmembrane (TM) helix, which associates to form homotetramers that bind the anti-influenza drug amantadine. However, the minimal fragment required for assembly and proton transport in cellular membranes has not been defined. Therefore, the conductance properties of truncation mutants expressed in Xenopus oocytes were examined. A short fragment spanning residues 21-61, M2(21-61), was inserted into the cytoplasmic membrane and had specific, amantadine-sensitive proton transport activity indistinguishable from that of full-length A/M2; an epitope-tagged version of an even shorter fragment, M2(21-51)-FLAG, had specific activity within a factor of 2 of the full-length protein. Furthermore, synthetic fragments including a peptide spanning residues 22-46 were found to transport protons into liposomes in an amantadine-sensitive manner. In addition, the functionally important His-37 residue pK(a) values are highly perturbed in the tetrameric form of the protein, a property conserved in the TM peptide and full-length A/M2 in both micelles and bilayers. These data demonstrate that the determinants for folding, drug binding, and proton translocation are packaged in a remarkably small peptide that can now be studied with confidence.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amantadine / pharmacology
  • Amino Acid Sequence
  • Animals
  • Biological Transport / drug effects
  • Dopamine Agents / pharmacology
  • Female
  • HeLa Cells
  • Humans
  • Hydrogen-Ion Concentration
  • Ion Channels / chemistry
  • Ion Channels / genetics
  • Ion Channels / physiology*
  • Membrane Potentials / drug effects
  • Microinjections
  • Molecular Sequence Data
  • Peptide Fragments / chemistry
  • Peptide Fragments / genetics
  • Peptide Fragments / physiology*
  • Protein Multimerization
  • Protons
  • Sequence Homology, Amino Acid
  • Thermodynamics
  • Viral Matrix Proteins / chemistry
  • Viral Matrix Proteins / genetics
  • Viral Matrix Proteins / physiology*
  • Xenopus


  • Dopamine Agents
  • Ion Channels
  • M2 protein, Influenza A virus
  • Peptide Fragments
  • Protons
  • Viral Matrix Proteins
  • Amantadine