SIGLEC9 (sialic acid binding Ig-like lectin 9)

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True   Likely   Speculative
Human Uniqueness Compared to "Great Apes": 
Likely Difference
Human Universality: 
Individual Universal (All Individuals Everywhere)
MOCA Domain: 
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Siglec-9 a sialic acid binding protein found on cells of the innate immune system, and may be involved in down-regulating innate immune responses. The homologous molecule found on the same cell types and chimpanzees and gorillas and appears to strongly prefer to bind to the non-human sialic acid Neu5Gc. This is in contrast to the human molecule, which prefers to binding the human sialic acid Neu5Ac. Thus the ancestral condition of the molecule was likely to prefer the sialic acid that was lost during hominid evolution. It is reasonable to speculate that the human molecule had to undergo adjustments to accommodate to bind Neu5Ac ligand. Indeed, there are several amino acid changes in the binding pocket off human Siglec-9 that a potentially involved in this evolution adjustment. It is unclear whether the evolutionary adjustment of binding is complete, and whether or not this has any consequences for modern human immunity or disease.


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 (Lineage Separation Event): 
Probable Appearance (Lineage Separation Event): 
Definite Appearance (Lineage Separation Event): 
Related MOCA Topics
Genetics Topic Attributes
Gene symbols follow the HUGO Gene Nomenclature Committee standard.
Gene Symbol Type of Human-Specific Changes
SIGLEC9 Accelerated Evolution, Amino Acid Change


  1. A uniquely human consequence of domain-specific functional adaptation in a sialic acid-binding receptor., Sonnenburg, Justin L., Altheide Tasha K., and Varki Ajit , Glycobiology, 2004 Apr, Volume 14, Issue 4, p.339-46, (2004)