Neuraminidase (NA)
and hemagglutinin (HA) are major membrane glycoproteins found on the surface of
influenza virus. Hemagglutinin binds to the sialic acid-containing receptors on
the surface of host cells during initial infection and at the end of an
infectious cycle. Hemagglutinin also plays a major role in the determination of
host range restriction and virulence. As a class I viral fusion protein,
hemagglutinin is responsible for penetration of the virus into the cell
cytoplasm by mediating the fusion of the membrane of the endocytosed virus
particle with the endosomal membrane. Binds to sialic acid-containing receptors
on the cell surface, bringing about the attachment of the virus particle to the
cell. This attachment induces virion internalization either through
clathrin-dependent endocytosis or through clathrin- and caveolin-independent
pathway. Plays a major role in the determination of host range restriction and
virulence. Class I viral fusion protein. Responsible for penetration of the
virus into the cell cytoplasm by mediating the fusion of the membrane of the
endocytosed virus particle with the endosomal membrane. Low pH in endosomes
induces an irreversible conformational change in HA2, releasing the fusion
hydrophobic peptide. Several trimers are required to form a competent fusion
pore.
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