UniProt functional annotation for P03474

UniProt code: P03474.

Organism: Influenza B virus (strain B/Lee/1940).
Taxonomy: Viruses; ssRNA negative-strand viruses; Orthomyxoviridae; Influenzavirus B.
Function: Catalyzes the removal of terminal sialic acid residues from viral and cellular glycoconjugates. Cleaves off the terminal sialic acids on the glycosylated HA during virus budding to facilitate virus release. Additionally helps virus spread through the circulation by further removing sialic acids from the cell surface. These cleavages prevent self-aggregation and ensure the efficient spread of the progeny virus from cell to cell. Otherwise, infection would be limited to one round of replication. Described as a receptor-destroying enzyme because it cleaves a terminal sialic acid from the cellular receptors. May facilitate viral invasion of the upper airways by cleaving the sialic acid moities on the mucin of the airway epithelial cells (By similarity). {ECO:0000250}.
Catalytic activity: Hydrolysis of alpha-(2->3)-, alpha-(2->6)-, alpha-(2->8)- glycosidic linkages of terminal sialic acid residues in oligosaccharides, glycoproteins, glycolipids, colominic acid and synthetic substrates.
Cofactor: Name=Ca(2+); Xref=ChEBI:CHEBI:29108; Evidence={ECO:0000269|PubMed:10547289, ECO:0000269|PubMed:15159560, ECO:0000269|PubMed:7880809}; Note=Binds 1 Ca(2+) ion per subunit. {ECO:0000269|PubMed:10547289, ECO:0000269|PubMed:15159560, ECO:0000269|PubMed:7880809};
Enzyme regulation: Inhibited by the neuraminidase inhibitors zanamivir (Relenza) and oseltamivir (Tamiflu). These drugs interfere with the release of progeny virus from infected cells and are effective against all influenza strains. Resistance to neuraminidase inhibitors is quite rare.
Subunit: Homotetramer. {ECO:0000269|PubMed:10547289, ECO:0000269|PubMed:15159560, ECO:0000269|PubMed:7880809}.
Subcellular location: Virion membrane {ECO:0000250}. Host apical cell membrane {ECO:0000250}; Single-pass type II membrane protein {ECO:0000250}. Note=Preferentially accumulates at the apical plasma membrane in infected polarized epithelial cells, which is the virus assembly site. In the virion, forms a mushroom-shaped spike on the surface of the membrane (By similarity). {ECO:0000250}.
Ptm: N-glycosylated. {ECO:0000269|PubMed:7880809}.
Miscellaneous: The influenza B genome consist of 8 RNA segments. Genetic variation of hemagglutinin and/or neuraminidase genes results in the emergence of new influenza strains. The mechanism of variation can be the result of point mutations or the result of genetic reassortment between segments of two different strains.
Similarity: Belongs to the glycosyl hydrolase 34 family. {ECO:0000305}.

Annotations taken from UniProtKB at the EBI.