The virus unmasked
The influenza A virus is deceptively simple – at its core are eight short single strands of RNA, the coding material for up to 14 proteins
Haemagglutinin is the structure that enables the virus to bind to host cells; neuraminidase is an enzyme that hydrolyses the polysaccharides that haemagglutinin binds to, helping to release new virus particles from the cell.
Adapted from Sebastian Kaulitzki/iStockphoto
There are at least 16 different types of haemagglutinin (H1–16) and nine types of neuraminidase (N1–9). Strains of flu virus are labelled according to which types of haemagglutinin and neuraminidase they carry – hence H1N1, H5N1, H7N9, etc. To date, only H1, H2 and H3 viruses have infected large numbers of people.
As well as haemagglutinin and neuraminidase, the virus coat includes some minor proteins. These include M2, an ion channel. The flow of ions through this channel enables the virus to uncoat inside the cell, freeing the strands of RNA to make new virus proteins.