Description
Neuraminidase (NA) is a major membrane glycoproteins found on the surface of influenza virus. NA specifically catalyzes the hydrolysis removal of terminal sialic acid residues from viral and cellular glycoconjugates. It is known that HA binds to the sialic acid-containing receptors on the surface of host cells during initial infection, and at the end of an infectious cycle, NA cleaves the HA-sialic acid bondage from the newly formed virions and the host cell receptors during budding. NA thus is described as a receptor-destroying enzyme which facilitates virus release and efficient spread of the progeny virus from cell to cell. NA is a single-pass type I I membrane protein which exists as a homotetramer, and the transmembrane domain is involved in lipid raft association duringintracellular transport. NA is suggested to play a role in the determination of host range restriction on replication and virulence. Nine subtypes of NA have been identified, and subtypes N1 and N2 have been positively linked to epidemics in man. Influenza A H1N1 virus is a subtype of influenza A virus. Some strains of H1N1 are endemic in humans and cause a small fraction of all influenzalike illness and a small fraction of all seasonal influenza. H1N1 strains caused a few percent of all human flu infections in 2004-2005. Other strains of H1N1 are endemic in pigs (swine influenza) and in birds (avian influenza). H1N1 was the most common cause of human influenza (flu) in 2009. In June 2009, the World Health Organization declared the new strain of swine-origin H1N1 as a pandemic. This strain is often called swine flu by the public media. This novel virus spread worldwide and had caused about 17,000 deaths by the start of 2010