Members of this family are found in the extracellular region of the cholecystokinin A receptor, where they adopt a tertiary structure consisting of a few helical turns and a disulphide-crosslinked loop. They are required for interaction of the cholecystokinin A receptor with it's corresponding hormonal ligand [1].

1: Molecular complex of cholecystokinin-8 and N-terminus of the cholecystokinin A receptor by NMR spectroscopy. Pellegrini M, Mierke DF; Biochemistry. 1999;38:14775-14783. PMID:10555959