This domain contains about 17 amino acid residues with two cysteines forming a disulfide bridge. It can be found in the antimicrobial peptides from Ranidae (riparian frogs), such as Nigroain-A antimicrobial peptide, Ranacyclin-T/E, Odorranain-B1 and Odorranain-B-RA1, which are secreted from frog skin.