**4. Identification of drug binding pathway**

172 Bioinformatics

studies of a possible mechanism for the H274Y mutation-induced drug resistance through water infiltration and destabilization of favourable drug packing. However, because no change in PG-SASA was observed during our simulations in the case of N294S for either protein,

**Figure 6.** Electrostatic surface potential of avian H5N1 and swine H1N1pdm neuraminidases in oseltamivir-bound simulations, revealing a positively charged pathway into the binding pocket. (A) through (C) show oseltamivir bound to H5N1 wild type, H274Y, and N294S drug-resistant mutant structures, respectively. (D) through (F) show oseltamivir bound to wild type, H274Y, and N294S drugresistant mutant structures, respectively. The outer columns show a close-up view of the binding pocket, highlighted as a subset of the enter protein shown in the central column. The positions of the

While alterations in hydrophobic sidegroup packing may explain in part the mechanism behind H274Y mutation-induced drug resistance, they fail to shed light on the role that the N294S mutation plays for oseltamivir binding inhibition. Initial investigations of the electrostatic surface potentials of drug-bound N1 neuraminidases have proposed that drug binding affinity is closely related to favourable charge-charge interactions with the

mutant residues are shown in green for residue 274 and 294 in the mutant systems

N294S induced drug resistance is probably due to a different mechanism.
