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On the Lower Susceptibility of Oseltamivir to Influenza Neuraminidase Subtype N1 than Those in N2 and N9

Ornjira Aruksakunwong ^*, Maturos Malaisree , Panita Decha , Pornthep Sompornpisut , Vudhichai Parasuk , Somsak Pianwanit  and Supot Hannongbua 

^* Department of Chemistry, Faculty of Science, Rangsit University, Pathumtani, 12000 Thailand; and Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand

Correspondence: Address reprint requests to Supot Hannongbua, Tel.: 66-22-187602; Fax: 66-22-187603; E-mail: supot.h{at}chula.ac.th.

Aiming to understand, at the molecular level, why oseltamivir (OTV) cannot be used for inhibition of human influenza neuraminidase subtype N1 as effectively as for subtypes N2 and N9, molecular dynamics simulations were carried out for the three complexes, OTV-N1, OTV-N2, and OTV-N9. The three-dimensional OTV-N2 and OTV-N9 initial structures were represented by the x-ray structures, whereas that of OTV-N1, whose x-ray structure is not yet solved, was built up using the aligned sequence of H5N1 isolated from humans in Thailand with the x-ray structure of the N2-substrate as the template. In comparison to the OTV-N2 and OTV-N9 complexes, dramatic changes were observed in the OTV conformation in the OTV-N1 complex in which two of its bulky side chains, N-acethyl (–NHAc) and 1-ethylproxy group (–OCHEt₂), were rotated to adjust the size to fit into the N1 catalytic site. This change leads directly to the rearrangements of the OTV's environment, which are i), distances to its neighbors, W-178 and E-227, are shorter whereas those to residues R-224, E-276, and E-292 are longer; ii), hydrogen bonds to the two nearest neighbors, R-224 and E-276, are still conserved in distance and number as well as percentage occupation; iii), the calculated ligand/enzyme binding free energies of –7.20, –13.44, and –13.29 kcal/mol agree with their inhibitory activities in terms of the experimental IC₅₀ of 36.1–53.2 nM, 1.9–2.7 nM, and 9.5–17.7 nM for the OTV-N1, OTV-N2, and OTV-N9 complexes, respectively; and iv), hydrogen-bond breaking and creation between the OTV and neighborhood residues are accordingly in agreement with the ligand solvation/desolvation taking place in the catalytic site.

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