Flu virus surface protein and antibody. Computer model showing the molecular structure of the neuraminidase glycoprotein enzyme found on the surface of the influenza (flu) virus, in complex with the antigen-binding fragment (Fab) of monoclonal antibody NC41. The presence of neuraminidase on the virus surface enables the virus to be released from the host cell. It is also a target for monoclonal antibody drugs that bind to it (seen here) and prevent influenza infection.