Hemagglutinin-neuraminidase

PDB 1usr EBI

Hemagglutinin-neuraminidase (HN) is a type of glycoprotein found on the surface of certain types of viruses, playing a crucial role in the viral life cycle. This molecule has dual enzymatic activities: it can cause red blood cells to clump together (hemagglutination) and it can cleave sialic acid groups from glycoproteins (neuraminidase activity). These functions are essential for the virus's ability to infect host cells and subsequently release new viral particles.

Structure and Function

The HN glycoprotein is a tetramer, consisting of four identical subunits that form a functional unit. Each subunit contains a site for hemagglutination activity and a separate site for neuraminidase activity. The structure of HN enables it to bind to sialic acid-containing receptors on the surface of host cells, facilitating viral entry. After replication, the neuraminidase activity helps in the release of newly formed viral particles by cleaving sialic acids from the host cell surface, preventing reattachment of the virus and allowing it to spread to infect other cells.

Role in Viral Pathogenesis

HN plays a significant role in the pathogenesis of viruses that possess this protein, such as paramyxoviruses, which include important human and animal pathogens like mumps virus, human parainfluenza viruses, and Newcastle disease virus. The interaction of HN with host cell receptors is a critical step in the viral infection process, determining the host range and tissue tropism of the virus. Moreover, the neuraminidase activity of HN is vital for the efficient spread of the virus within the host organism.

Immune Response and Vaccine Development

The HN protein is a key target for the immune response against viruses that carry this molecule. Antibodies that block the binding sites or enzymatic activities of HN can neutralize the virus, preventing it from infecting cells. This has made HN an important antigen for vaccine development. Vaccines that elicit a strong immune response against HN can potentially confer protection against the diseases caused by HN-bearing viruses.

Clinical Significance

Understanding the structure and function of HN is crucial for the development of antiviral drugs and vaccines. Inhibitors that target the neuraminidase activity of HN, similar to those used against influenza virus neuraminidase, could be effective in treating infections caused by HN-bearing viruses. Additionally, the hemagglutination activity of HN makes it a useful tool in laboratory diagnostics for virus identification and quantification.

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