AN INFLUENZA VIRUS NEURAMINIDASE VARIANT WITH DECREASED SENSITIVITY TO THE NEURAMINIDASE INHIBITOR 4-GUANIDINO-NEU5AC2EN. J.N.Varghese, P.M.Colman, T.J. Blick, T.Tiong, S.Sahasrabudhe, & J.L. McKimm-Breschkin, Biomolecular Research Institute, Parkville, Victoria 3052.

A variant of influenza virus with 1000-fold less sensitivity in vitro to the anti-influenza drug 4-guanidino-Neu5Ac2en has been isolated by multiple passage of influenza virus NWS/G70C with the N9 subtype neuraminidase in MDCK cells in the presence of 4-guanidino-Neu5Ac2en. The crystal structure of this variant of influenza virus NWS/G70C neuraminidase, has been determined to 2 Angstrom resolution for the native enzyme and a complex with 4-guanidino-Neu5Ac2en. This study has confirmed a single site mutation of a conserved active site residue in the floor of the active site pocket, Glu 119 to Gly, and suggests that the reduced affinity for the 4-guanidino derives partly from loss of stabilising interaction between the guanidino moiety and the carboxylate at residue 119, and partly from alterations in the solvent structure of the active site. A water molecule was found close to the position formerly occupied by one of the glutamic acid carboxylate oxygens in the wild type structure, and this water molecule Hydrogen-bonds with the secondary amino nitrogens of an active site arginine (156).