Influenza Virus Structure and Surface Proteins
Influenza viruses belong to the Orthomyxoviridae family and contain single-stranded, segmented RNA. The internal structure consists of a ribonucleoprotein surrounded by matrix protein M1. The outer lipid envelope (supercapsid) contains surface glycoproteins that determine the virus subtype and act as antigens.
Key surface structures include:
- Hemagglutinin (H) — mediates virion attachment (adhesion) to sialic acids on respiratory epithelial cells.
- Neuraminidase (N) — cleaves hemagglutinin bonds with cellular receptors, facilitating viral entry and release after replication.
Adsorption, Penetration, and the Role of the M2 Protein
The infectious process begins with the virus attaching to the target cell via the interaction of hemagglutinin with sialic acids. The virion then enters the cell via endocytosis, forming an endosome.
Inside the endosome, the environment becomes acidified. Hydrogen ions enter the viral particle through the proton channel formed by the M2 protein. This process leads to the dissociation of the matrix protein and ribonucleoproteins—deproteinization occurs, releasing viral RNA into the cytoplasm.
The pharmacological agent rimantadine selectively blocks M2 ion channels, preventing endosomal acidification and viral uncoating.
Intracellular Synthesis, Assembly, and Release of Virions
The released viral RNA is transported into the host cell nucleus, where viral RNA polymerase mediates genome replication and viral mRNA transcription. The resulting mRNA enters the cytoplasm, where host ribosomes synthesize the required proteins.
New virions assemble at the cell membrane, after which the viral particles bud off. In the final stage, hemagglutinin retains new virions on the surface of the infected cell.
The enzyme neuraminidase cleaves this bond, ensuring the final separation of viral particles. The drug oseltamivir inhibits neuraminidase, blocking the spread of the infection.