Hemagglutinin-neuraminidase refers to a single viral protein that has both hemagglutinin and neuraminidase activity. This is in contrast to the proteins found in influenza, where both functions exist but in two separate proteins. However it does show a structural similarity to influenza viral neuraminidase and has a six-bladed beta-propeller structure. Hemagglutinin-neuraminidase allows the virus to stick to a potential host cell, and cut itself loose if necessary. Hemagglutinin-neuraminidase can be found in a variety of paramyxoviruses including mumps virus, human parainfluenza virus 3, and the avian pathogen Newcastle disease virus.