[2] The crystal structure of FAS1 domains 3 and 4 of fasciclin I from Drosophila melanogaster (Fruit fly) has been determined, revealing a novel domain fold consisting of a seven-stranded beta wedge and at least five alpha helices; two well-ordered N-acetylglucosamine groups attached to a conserved asparagine are located in the interface region between the two FAS1 domains.

[3] Fasciclin I is an insect neural cell adhesion molecule involved in axonal guidance that is attached to the membrane by a GPI-anchored protein.

FAS1 domains are present in many secreted and membrane-anchored proteins.

Proteins known to contain a FAS1 domain include: The FAS1 domains of both human periostin and BIgH3 proteins were found to contain vitamin K-dependent gamma-carboxyglutamate residues.

[8] Gamma-carboxyglutamate residues are more commonly associated with GLA domains, where they occur through post-translational modification catalysed by the vitamin K-dependent enzyme gamma-glutamylcarboxylase.