Three of the residues identified here (N224, Q226 and T318) have been strictly conserved among H5 HA proteins isolated since 2003. However, as H5N1 viruses continue to evolve and infect people, receptor-binding variants of H5N1 viruses, including avian–human reassortant viruses as tested here, may emerge. One of the four mutations we identified in our transmissible virus, the N158D mutation, results in loss of a glycosylation site. Many H5N1 viruses isolated in the Middle East, Africa, Asia and Europe do not have this glycosylation site. Therefore, only three nucleotide changes are needed for the HA of these viruses to support efficient transmission in ferrets. In addition, the H5N1 viruses circulating in these geographic areas also possess a glutamic-acid-to-lysine mutation at position 627 in the PB2 protein, which promotes viral replication in certain mammals, including humans40, 45. Therefore, these viruses may be several steps closer to those capable of efficient transmission in humans and are of concern.http://www.nature.com/nature/journal/va ... 10831.htmlThe above description notes the widespread presence of N158D (and/or T160A), which eliminates the glycosylation site at position 158. Also noted is E627K, which is fixed in clade 2.2.
However. no mention is made of A242S or A242T which are found in transmitting H5N1 in ferrets. Both chngaes crreate a glycosylation site at position 240, and most clade 2.2.1 F sequences in Egypt or Israel collected since 2009 have A242T and the associated glycosylation at position 240.
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