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 crys-tallographic 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.
|Original language||English (US)|
|Number of pages||5|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Nov 3 2009|
- Binding site
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