Three-dimensional structure of influenza A/Tern/Australia/G70C/75 N9 neuraminidase and its complex with the inhibitor 2-deoxy-2,3-dehydro N-acetyl neuraminic acid

There is currently no way to effectively halt the spread of influenza due to its ability to undergo antigenic variation. Antigenic variation results in variability of the three-dimensional structures of two viral surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA). By altering these two proteins, the virus escapes recognition by the host immune system and new strains of virus continually arise in the population.; The target for neutralizing antibodies is primarily the HA which is responsible for the initial attachment of the virus and subsequent fusion with the host cell membrane. Vaccines incorporate viruses from the most prevalent circulating strains during annual seasonal epidemics. But due to the variability of the surface antigens, vaccines are totally ineffective after several years and must be constantly updated and redesigned at great expense.; As an alternative to vaccine development, efforts can be geared towards the design of specific compounds against a specific viral target. Neuraminidase is a good candidate for anti-influenza drug design. A potent inhibitor would not destroy the virus' ability to initially infect hosts, but would halt virus spread. A permitted single round of viral replication would provide an additional boost to the host by stimulating the host's own immune defenses.; Detailed structural information at atomic resolution must be obtained to design specific inhibitors. At this time, the only satisfactory method for obtaining this information is by X-ray crystallography. Single crystal X-ray diffraction was used in this dissertation to obtain three-dimensional information at atomic resolution for avian N9 influenza neuraminidase, A/Tern/Australia/G-70C/75, by the method of multiple isomorphous replacement (MIR). The structure of the enzyme and its complex with the inhibitor 2-deoxy-2,3-dehydro, N-acetyl neuraminic acid are reported to 2.5 A and 2.8 A, respectively.; The native and ligand complex crystals are isomorphous and belong to cubic space group I432. Unit cell lengths are 183.8 A. The models refine to an R-factor of 0.25 for the native, and 0.24 for the inhibitor complex. The final geometric constraints of 0.02 A for bond lengths and 4{dollar}spcirc{dollar} for bond angles suggest that the models have acceptable geometry. Density for the weak inhibitor 2-deoxy-2,3-dehydro N-acetyl neuraminic acid is well-defined in the substrate-binding site. This is the first published report of a neuraminidase inhibitor complex.