Hey folks, I did a bit of a read on this topic tonight and have...

Hey folks,
I did a bit of a read on this topic tonight and have distilled what I learnt into the following two paragraphs. This mutation is important as it changes the way the virus gains access to different types of cells. Cheers,

The HA is the binding protein for the virus. The D225G is a sequence of amino acids in the HA that binds the virus to the salic sugars on the host cell. Changes to amino acid composition/sequence will alter the 3d structure of the binding site (perhaps even the HA protein) and will affect the way it interacts with the host’s cell surface markers (salic sugars).

Once the HA is bound to the cell surface, the virus is enveloped by the host cell ONLY after a protease from the host cell cleaves the HA-sugar complex. The host’s proteases are critical to the spread of the virus. Proteases are programmed to cleave between two specific amino acids residues, so any shift in the sequence of amino acids on the HA binding site (ie the D225G) will change its potential for cleavage. Highly virulent strains, ie avian flu, express a sequence of amino acids in the binding complex that can be targeted by many different proteases, and allows the virus to infect multiple cell types/tissues and spread throughout the body.