STRUCTURE OF INFLUENZA-VIRUS NEURAMINIDASE B LEE/40 COMPLEXED WITH SIALIC-ACID AND A DEHYDRO ANALOG AT 1.8-ANGSTROM RESOLUTION - IMPLICATIONS FOR THE CATALYTIC MECHANISM/

Neuraminidase is one of the two glycoprotein spikes protruding from th e influenza virus membrane. We have determined by X-ray crystallograph y the native structure of B/Lee/40 neuraminidase (NA) and the structur es of its crystals soaked with a substrate, N-acetylneuraminyllactose (NANL), and an inhibitor, 2-deoxy-2,3-didehydro-N-acetylneuraminic aci d (DANA) at 1.8-Angstrom resolution. NANL was hydrolyzed by the crysta lline NA to generate the product N-acetylneuraminic acid (NANA, also k nown as sialic acid), which is still able to bind to NA. In the differ ence Fourier map of the presumed NA-NANA complex, the moiety bound in the active site had a distorted boat conformation of NANA, but there i s no significant electron density for O2. The structure of the bound m oiety is not identical to that of chemically synthesized DANA soaked i nto NA crystals. Prolonged incubation of NANA with NA in solution at r oom temperature produced only a trace amount of DANA as detected by NM R. On the basis of our studies, a mechanism is proposed for the enzyma tic hydrolysis by influenza virus neuraminidase.