Recombining H1N1 and H5N1 Is Very Scary

Avian Flu Acquired a Basic Internalization Domain in the 1990’s

Avian flu was simply for the birds until its hemagglutinin (the H or H5N1) acquired an extra four basic amino acids that provided another way into human cells.

Basic Amino Acids Accumulate in the Hemagglutinin

During the early 1990’s isolates of avian flu, H5N1 started to appear that eventually developed six basic amino acids in a stretch about 340 residues from the amino terminus. These basic amino acids are thought to be an adaptation to decrease inactivation by a host protease.

H5N1
~PQRE TRGLFG~ ABB88379 Mexico 1994
~PQRK TRGLFG~ ABQ84472 Italy 1993
~PQRK ETRGLFG~ ACH88842 USA 1993
~PQRKRKRKTRGLFG~AAC58990 Mexico 1995
~PQRE RKKRGLFG~ ABQ84473 Italy 1997
~PQRERRRKKRGLFG~ AAD37782 China 1996
~PQRK RKTRGLFG~ ACL79965 Mexico 1994
H1N1
~PSIQ SRGLFG~ AAF87275

The red area is the region that has accumulated the basic amino acids (R and K). Note that the novel H1N1, does not yet have this region.

The New Basic Region Looks Like an Internalization Signal

Those who have followed this blog know that I have an interest in heparin binding domains, groups of basic amino acids (K for lysine and R for arginine) of proteins that bind the common acidic extracellular polysaccharide heparin. Most recently I have been focusing on unusual triplets of basic amino acids that are found in the proteins of allergens and autoantigens. These basic triplets are similar to the basic quartets that are used as signals to move proteins from cytoplasm into the nucleus of cells, i.e. the nuclear localization signal (NLS).

Basic Sextet for Internalization and More

The newly evolved basic sextet, RRRKKR, should be readily transported into cells by the mannose receptor and then taken into the nucleus, because it would also act as a NLS. This should also mean that the new H5N1 viruses with this hemagglutinin should attach to numerous cells of the immune system and potentially transported to other areas of the body.

Is this Dangerous?

I don’t know what the likelihood of recombination between H5N1 and H1N1 is if a bird, pig or human is infected with both nor is the impact of acquisition of the basic sextet by H1N1 on virulence known, but the acquisition of the basic sextet occurred at the same time that H5N1 moved from birds to people and became lethal.

Basic Sextet May Explain New Entry for H5N1

H5N1 has recently been found to infect tissue that lack the sialic acid sugars that are the typical target for avian flu. The new targets are not known. I would start to suspect the mannose receptor that I have postulated to be involved in initiation of allergy and autoimmunity.