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Since hemagglutinin is the major surface protein of the influenza A virus and is essential to the entry process, it is the primary target of neutralizing antibodies. [citation needed] These antibodies against flu have been found to act by two different mechanisms, mirroring the dual functions of hemagglutinin:
This attachment is required for efficient transfer of flu virus genes into cells, a process that can be blocked by antibodies that bind to the hemagglutinin proteins. One genetic factor in distinguishing between human flu viruses and avian flu viruses is that avian influenza HA bind to alpha 2-3 sialic acid receptors while human influenza HA ...
Hemagglutinins are small proteins that extend from the surface of the virus membrane as spikes that are 135 Angstroms (Å) in length and 30-50 Å in diameter. [19] Each spike is composed of three identical monomer subunits, making the protein a homotrimer.
Influenza viruses A and B are estimated to have diverged from a single ancestor around 4,000 years ago, while the ancestor of influenza viruses A and B and the ancestor of influenza virus C are estimated to have diverged from a common ancestor around 8,000 years ago. [40] Outbreaks of influenza-like disease can be found throughout recorded history.
Viral neuraminidase cleaves terminal sialic acid residues from glycan structures on the surface of the infected cell. This promotes the release of progeny viruses and the spread of the virus from the host cell to uninfected surrounding cells. Neuraminidase also cleaves sialic acid residues from viral proteins, preventing aggregation of viruses.
Influenza A viruses are further classified, based on the viral surface proteins hemagglutinin (HA or H) and neuraminidase (NA or N). 18 HA subtypes (or serotypes) and 11 NA subtypes of influenza A virus have been isolated in nature. Among these, the HA subtype 1-16 and NA subtype 1-9 are found in wild waterfowl and shorebirds and the HA ...
“For example, if a human gets infected with a bird flu and also carries a human influenza A virus, these two viruses can exchange genetic material. This is known as genetic shift,” Michael ...
Examples of class II viral fusion proteins include the dengue virus E protein, and the west nile virus E protein. [5] [6] Class III: Structural conformation is a combination of features from Class I and Class II viral membrane fusion proteins. An example of a Class III viral fusion protein is the rabies virus glycoprotein, G. [6]