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Influenza hemagglutinin (HA) or haemagglutinin [p] (British English) is a homotrimeric glycoprotein found on the surface of influenza viruses and is integral to its infectivity. Hemagglutinin is a class I fusion protein , [ 1 ] [ 2 ] having multifunctional activity as both an attachment factor and membrane fusion protein .
For influenza A virus and influenza B virus, hemagglutinin (HA) and neuraminidase (NA) are encoded on one segment each, whereas influenza C virus and influenza D virus encode a hemagglutinin-esterase fusion (HEF) protein on one segment that merges the functions of HA and NA.
Structure of Influenza, showing neuraminidase marked as NA and hemagglutinin as HA Influenza virus replication, showing how in step 6 the neuraminidase and hemagglutinin proteins incorporated into the host cell's membrane are used to escape. Viral neuraminidase is a type of neuraminidase found on the surface of influenza viruses that enables the
Illustration showing influenza virus attaching to cell membrane via the surface protein hemagglutinin. Hemagglutinins (alternatively spelt haemagglutinin, from the Greek haima, 'blood' + Latin gluten, 'glue') are homotrimeric glycoproteins present on the protein capsids of viruses in the Paramyxoviridae and Orthomyxoviridae families.
To unambiguously describe a specific isolate of virus, researchers use the Influenza virus nomenclature, [21] which describes, among other things, the subtype, year, and place of collection. Some examples include: [22] A/Rio de Janeiro/62434/2021 (H3N2). [22] The starting A indicates that the virus is an influenza A virus.
3D model of the flu virion. (M2 labeled in white.) The Matrix-2 (M2) protein is a proton-selective viroporin, integral in the viral envelope of the influenza A virus. The channel itself is a homotetramer (consists of four identical M2 units), where the units are helices stabilized by two disulfide bonds, and is activated by low pH.
There are four different types of influenza virus: A, B, C, and D. Influenza C usually causes only mild illness while D mostly affects animals, especially cattle.
Influenza A virus structure. The influenzavirus virion is pleomorphic; the viral envelope can occur in spherical and filamentous forms. In general, the virus's morphology is ellipsoidal with particles 100–120 nm in diameter, or filamentous with particles 80–100 nm in diameter and up to 20 μm long. [5]