Imidazole-imidazole hydrogen bonding in the pH sensing Histidine sidechains of Influenza A M2

The arrangement of histidine sidechains in influenza A M2 tetramer determines their pKa values, which define pH controlled proton conduction critical to the virus lifecycle. Both water associated and hydrogen bonded Imidazole-Imidazolium histidine quaternary structures have been proposed, based on crystal structures, and NMR chemical shifts, respectively. Here we show, using the conduction domain construct of M2 in lipid bilayers, that the imidazole rings are hydrogen bonded even at a pH of 7.8 in the neutral charge state.\n\nAn intermolecular 8.9 {+/-} 0.3 Hz 2hJNN hydrogen bond is observed between H37 N{varepsilon} and N{delta} recorded in a fully protonated sample with 100 kHz magic-angle spinning. This interaction could not be detected in the drug-bound sample.