A new family of growth factor-like peptides. 'Trefoil' disulphide loop structures as a common feature in breast cancer associated peptide (pS2), pancreatic spasmolytic polypeptide (PSP), and frog skin peptides (spasmolysins)

Abstract

Four peptides present in completely different biological sources have been shown to exhibit a large degree of structural similarity. The peptides include: (i) a 60 amino acid residue breast cancer associated pS2 peptide isolated from human gastric juice and the culture media of the human breast cancer cell line MCF-7; (ii) a 106 amino acid residue pancreatic spasmolytic polypeptide (PSP) isolated from porcine pancreas and pancreatic juice; and (iii) a 49 and 50 amino acid residue peptide predicted from a cDNA isolated from the skin of the frog, Xenopus laevis. These peptides are characterized by having one (pS2 and the frog peptides) or two (PSP) domains of a highly conserved 38-39 amino acid residue consensus sequence not found in any other known peptides or proteins. The domain sequences contain 6 cysteine residues in nearly the same positions and it is suggested that these 6 residues are linked by 3 disulphide bonds to form a characteristic 'trefoil' disulphide loop structure common in all four peptides. From the sources of which the peptides have been isolated and from experiments showing that PSP has a growth factor stimulatory effect on MCF-7 cells, it is further suggested that these peptides may represent members of a new family of growth factors.