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Official Full Name
Neuraminidase
Background
Influenza virus belongs to the genus orthomyxovirus in the family of Orthomyxoviridae. There are 4 antigens present, the haemagglutinin (HA), neuraminidase (NA), nucleocapsid (NA), the matrix (M) and the nucleocapsid proteins.
Synonyms
Influenzavirus B neuraminidase; NA; Neuraminidase

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 [1].

Gene function

  • Neuraminidase 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.
  • Neuraminidase 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.
  • Neuraminidase may facilitate viral invasion of the upper airways by cleaving the sialic acid moieties on the mucin of the airway epithelial cells.
  • Neuraminidase maybe plays a role in the budding process through its association with lipid rafts during intracellular transport.
  • Neuraminidase may display a raft-association independent effect on budding.
  • Neuraminidase plays a role in the determination of host range restriction on replication and virulence. Sialidase activity in late endosome/lysosome traffic seems to enhance virus replication.

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 [2].

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 [3].

Conclusions

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 [4].

References:

  1. Kamali, A. and M. Holodniy, Influenza treatment and prophylaxis with neuraminidase inhibitors: a review. Infect Drug Resist, 2013. 6: p. 187-98.
  2. Piralla, A., et al., Multiple clusters of A(H1N1)pdm09 virus circulating in severe cases of influenza during the 2010-2011 season: a phylogenetic and molecular analysis of the neuraminidase gene. J Med Virol, 2013. 85(6): p. 944-52.
  3. Gnirss, K., et al., Tetherin Sensitivity of Influenza A Viruses Is Strain Specific: Role of Hemagglutinin and Neuraminidase. J Virol, 2015. 89(18): p. 9178-88.
  4. Eichelberger, M.C. and H. Wan, Influenza neuraminidase as a vaccine antigen. Curr Top Microbiol Immunol, 2015. 386: p. 275-99.