A sequon is a sequence of three consecutive amino acids in a protein
that can serve as the attachment site to a polysaccharide (sugar) called an
N-linked-Glycan. This is a polysaccharide
linked to the protein via the nitrogen atom in the side chain of
asparagine (Asn). A
sequon is either Asn-X-Ser or Asn-X-Thr, where X is any amino
acid except proline. The term appears to have been first used by
Derek Marshall
.
The textbook by Dwek et al. states that "Occasionally, such as in the leukocyte surface protein (CD69), the
amino acid sequence Asn-Xaa- Cys is an acceptable sequon for the
addition of N-linked glycans"
The term is not frequently used. For example it does not appear in the textbooks
Essentials of Glycobiology, edited by A. Varki or Introduction to Glycobiology
by Maureen E. Taylor and Kurt Drickamer.