Influenza virus causes severe
respiratory infections that are responsible for up to half a million deaths worldwide each year. Two inhibitors targeting viral
neuraminidase have been approved to date (
oseltamivir,
zanamivir). However, the rapid development of antiviral drug resistance and the efficient transmission of resistant viruses among humans represent serious threats to public health. The approved
influenza neuraminidase inhibitors have (oxa)
cyclohexene scaffolds designed to mimic the
oxonium transition state during enzymatic cleavage of
sialic acid. Their active forms contain a carboxylate that interacts with three
arginine residues in the
enzyme active site. Recently, the
phosphonate group was successfully used as an isostere of the carboxylate in
oseltamivir, and the resulting compound,
tamiphosphor, was identified as a highly active
neuraminidase inhibitor. However, the structure of the complex of this promising inhibitor with
neuraminidase has not yet been reported. Here, we analyzed the interaction of a set of
oseltamivir and
tamiphosphor derivatives with
neuraminidase from the A/California/07/2009 (H1N1) influenza virus. We thermodynamically characterized the binding of
oseltamivir carboxylate or
tamiphosphor to the
neuraminidase catalytic domain by
protein microcalorimetry, and we determined crystal structure of the catalytic domain in complex with
tamiphosphor at 1.8 Å resolution. This structural information should aid rational design of the next generation of
neuraminidase inhibitors.