An amantadine-sensitive chimeric BM2 ion channel of influenza B virus has implications for the mechanism of drug inhibition

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National Academy of Sciences

RESUMO

Influenza A virus M2 (A/M2) and the influenza B virus BM2 are both small integral membrane proteins that form proton-selective ion channels. Influenza A virus A/M2 channel is the target of the antiviral drug amantadine (and its methyl derivative rimantadine), whereas BM2 channel activity is not affected by the drug. The atomic structure of the pore–transmembrane (TM) domain peptide has been determined by x-ray crystallography [Stouffer et al. (2008) Nature 451:596–599] and of a larger M2 peptide by NMR methods [Schnell and Chou (2008) Nature 451:591–595]. The crystallographic data show electron density (at 3.5 Å resolution) in the channel pore, consistent with amantadine blocking the pore of the channel. In contrast, the NMR data show 4 rimantadine molecules bound on the outside of the helices toward the cytoplasmic side of the membrane. Drug binding includes interactions with residues 40–45 and a polar hydrogen bond between rimantadine and aspartic acid residue 44 (D44). These 2 distinct drug-binding sites led to 2 incompatible drug inhibition mechanisms. We have generated chimeric channels between amantadine-sensitive A/M2 and amantadine-insensitive BM2 designed to define the drug-binding site. Two chimeras containing 5 residues of the A/M2 ectodomain and residues 24–36 of the A/M2 TM domain show 85% amantadine/rimantadine sensitivity and specific activity comparable to that of WT BM2. These functional data suggest that the amantadine/rimantadine binding site identified on the outside of the 4 helices is not the primary site associated with the pharmacologic inhibition of the A/M2 ion channel.

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