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Influenza A contains eight gene segments that encode eleven proteins, including hemagglutinin (HA) and neuraminidase (NA) glycoproteins, which is a negative sense RNA virus with a low fidelity RNA polymerase. The influenza A virus attach to sialic acid residues on host cells by via HA, which then initiates the infection. Once cells are infected, there are direct necrotic effects on the respiratory cell as the virus begins to replicate by using the host cell machinery and then shuts off host cell RNA transcription and translation.
Neuraminidase is a receptor-destroying enzyme for it cleaves a terminal sialic acid from the cellular receptors. Neuraminidase preferentially accumulates at the virus assembly site, where is apical plasma membrane in infected polarized epithelial cells. Neuraminidase uses lipid rafts for cell surface transport and apical sorting. In the virion, it forms a mushroom-shaped spike on the surface of the membrane. Zanamivir (Relenza) and oseltamivir (Tamiflu) are the inhibitors of Neuraminidase. These drugs interfere with the release of progeny virus from infected cells and are effective against all influenza strains.
Fig.1. The role of NA in the influenza virus’ life cycle .
The importance of Neuraminidase research
Influenza A virus (FLUAV) infection is responsible for substantial global morbidity and mortality, and understanding how the virus evades the immune defenses of the host may uncover novel targets for antiviral intervention. The molecular characterization of circulating influenza A viruses is essential to detect mutations potentially involved in increased virulence, drug resistance and immune escape .
Tetherin is an antiviral effector molecule of the innate immune system which can contribute to control of viral invasion. Previous study observed that several pandemic FLUAV strains can counteract tetherin via their HA and NA proteins identifies these proteins as novel tetherin antagonists and indicates that HA/NA-dependent inactivation of innate defenses may play a part in the efficient spread of pandemic FLUAV .
Clinical studies demonstrate that licensed seasonal vaccines contain immunogenic amounts of Neuraminidase, but the contribution of this immunity to vaccine efficacy is not known currently. New types of influenza vaccines could be designed to elicit Neuraminidase immunity. Because Neuraminidase induces heterologous immunity, it could be an essential constituent of universal influenza vaccines that focus on protect against unexpected emerging viruses .