Sequon

A sequon is a specific amino acid sequence in a protein that is glycosylated with an N-linked glycan. The consensus sequence for N-linked glycosylation is Asn-X-Ser/Thr, where Asn is asparagine, X is any amino acid except proline, and Ser/Thr is either serine or threonine. The asparagine residue within this sequon is modified by the addition of a glycan.

The presence of a sequon does not guarantee glycosylation. Factors such as the protein's three-dimensional structure and the accessibility of the sequon to glycosylation enzymes (oligosaccharyltransferases) in the endoplasmic reticulum lumen influence whether glycosylation actually occurs. Some sequons are therefore considered "cryptic" because they are present in the protein sequence but are not glycosylated.

The N-linked glycosylation of proteins is a critical post-translational modification with diverse functions, including protein folding, stability, trafficking, and interactions with other molecules. Mutations that alter or eliminate a sequon can significantly affect protein function and can be associated with various diseases.