CRYSTAL-STRUCTURE OF A DISULFIDE-LINKED TREFOIL MOTIF FOUND IN A LARGE FAMILY OF PUTATIVE GROWTH-FACTORS

Porcine pancreatic spasmolytic polypeptide (PSP) belongs to a large fa mily of homologous growth factor-like polypeptides characterized by a disulfide-linked ''trefoil motif,'' duplicated and conserved in variou s family members. PSP contains two trefoil motifs, has several pharmac ological actions on the gut, and has growth factor properties on epith elial cells in vitro. The human PSP analogue, human spasmolytic polype ptide, appears to be involved in many regenerative situations and, esp ecially, in healing gastrointestinal ulcers. One member of the trefoil family, pS2, is secreted in almost-equal-to 50% of estrogen-dependent human breast carcinomas, which has led to its use as a tumor prognost ic marker. Both pS2 and human spasmolytic polypeptide are also widely expressed in chronic gastrointestinal ulcerative conditions such as Cr ohn disease. Here we report the three-dimensional structure at 2.6-ang strom resolution of a trefoil-containing protein, namely PSP, purified from porcine pancreas. The structure shows two homologous domains tha t share a supersecondary structure and disulfide bond pattern. The two domains pack asymmetrically giving rise to a number of protruding loo ps, exposed clefts, and an unusual electrostatic surface potential. Kn owledge of the structure of PSP should allow the design of mutants to investigate further the function of PSP and other trefoil-containing p eptides.