Neuraminidase (NA) is the second most abundant glycoprotein
on the surface of influenza virus. It cleaves the linkage between
hemagglutinin (HA) and cell surface receptors, and thus helps the
release and spread of influenza virus.NA is a tetramer of identical
subunits anchored in the lipidbilayer by a hydrophobic amino-terminal sequence.
The active site of the enzyme is located in a crater on the top
of each monomer. Inhibition of NA enzyme activity by either NAspecific
antibodies or drugs can limit the spread of influenza virus,
thus reduce viral load and disease symptoms. Antibodies against
NA, while do not prevent influenza virus attachment and entry into
cells, sharply limit virus spread and thereby
contribute to immunity against influenza virus.