Alpha2-6-linked Sialic Acid Expression

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Human Uniqueness Compared to "Great Apes": 
Relative Difference
Human Universality: 
Individual Universal (All Individuals Everywhere)
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The alpha2-6 linkage represents one of three common glycosidic linkages (attachments) of the cell surface sugar, sialic acid. The presence of sialic acid in this linkage to glycoproteins on cell surfaces is determined mainly by the activity of the sialyltransferase gene ST6GAL1. There are differences between humans and other hominids with respect to this cell surface structure. Chief among them is the strong presence of the structure on the bronchial epithelial lining of humans, but not in other hominids. A similar difference exists with respect to red blood cells. In contrast, certain tissues of other hominids show higher levels of alpha2-6-linked sialic acids than humans (including cords and vessels of the spleen, lymphoid follicles, and bile ducts in the liver). The human expression of alpha2-6-linked sialic acids on the lining of the human airways can explain the specificity of influenza virus invasion and the relative protection of humans from the "bird flu". The available data predicts that other hominids would be much more susceptible to the "bird flu".


Timing of appearance of the difference in the Hominin Lineage as a defined date or a lineage separation event. The point in time associated with lineage separation events may change in the future as the scientific community agrees upon better time estimates. Lineage separation events are defined in 2017 as:

  • the Last Common Ancestor (LCA) of humans and old world monkeys was 25,000 - 30,000 thousand (25 - 30 million) years ago
  • the Last Common Ancestor (LCA) of humans and chimpanzees was 6,000 - 8,000 thousand (6 - 8 million) years ago
  • the emergence of the genus Homo was 2,000 thousand (2 million) years ago
  • the Last Common Ancestor (LCA) of humans and neanderthals was 500 thousand years ago
  • the common ancestor of modern humans was 100 - 300 thousand years ago

Possible Appearance: 
6,000 thousand years ago
Probable Appearance: 
2,000 thousand years ago
Definite Appearance: 
100 thousand years ago
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  1. Human-specific regulation of alpha 2-6-linked sialic acids, Gagneux, P., Cheriyan M., Hurtado-Ziola N., van der Linden E. C., Anderson D., McClure H., Varki Ajit, and Varki Nissi M. , J Biol Chem, Nov 28, Volume 278, Number 48, p.48245-50, (2003)