Neuramidase flu proteins (yellow), artwork. Neuramidase is a membrane (surface) protein for the infuenza virus. An example is H1N1 flu virus, where N1 stands for neuramidase 1. This protein is the second most abundant membrane protein of flu viruses. Also called sialidase, it is a target for the immune system and antiviral drugs like oseltamivir (Tamiflu) and zanamivir (Relenza). By disrupting the functioning of neuramidase, these drugs prevent the viruses from binding to host cells.