How does each substituent functional group of oseltamivir lose its activity against virulent H5N1 influenza mutants?

To reveal the source of oseltamivir-resistance in influenza (A/H5N1) mutants, the drug-target interactions at each functional group were investigated using MD/LIE simulations. Oseltamivir in the H274Y mutation primarily loses the electrostatic and the vdW interaction energies at the -NH3+ and -OCHEt2 moieties corresponding to the weakened hydrogen-bonds and changed distances to N1 residues. Differentially, the N294S mutation showed small changes of binding energies and intermolecular interactions. Interestingly, the presence of different conformations of E276 positioned between the -OCHEt2 group and the mutated residue is likely to play an important role in oseltamivir-resistant identification. In the H274Y mutant, it moves towards the -OCHEt2 group leading to a reduction in hydrophobicity and pocket size, whilst in the N294S mutant it acts as the hydrogen network center bridging with R224 and the mutated residue S294. The molecular details have answered a question of how the H274Y and N294S mutations confer the high- and medium-level of oseltamivir-resistance to H5N1.