This family consists of cuticle protein 7 isoforms that are isolated from the carapace cuticle of a juvenile horseshoe crab, Limulus polyphemus. There are 3 isoforms of cuticle protein 7. The 3 isoforms are N-terminally blocked but could be deblocked by treatment with pyroglutaminase, showing that the N-terminal residue is a pyroglutamine residue [1].

1: Cuticular proteins from the horseshoe crab, Limulus polyphemus. Ditzel N, Andersen SO, Hojrup P; Comp Biochem Physiol B Biochem Mol Biol 2003;134:489-497. PMID:12628379