Protein Domain : P-type trefoil, chordata IPR017994

Type	Family
Description	A cysteine-rich domain of approximately forty five amino-acid residues has been found in some extracellular eukaryotic proteins [ , , , ]. It is known as either the 'P', 'trefoil' or 'TFF' domain, and contains six cysteines linked by three disulphide bonds with connectivity 1-5, 2-4, 3-6. This leads to a characteristic three leafed structure ('trefoil'). The P-type domain is clearly composed of three looplike regions. The central core of the domain consists of a short two-stranded antiparallel β-sheet, which is capped by an irregular loop and forms a central hairpin (loop 3). The β-sheet is preceded by a short α-helix, with majority of the remainder of the domain contained in two loops, which lie on either side of the central hairpin.This domain has been found in a variety of extracellular eukaryotic proteins [ , , ], including:Protein pS2 (TFF1), a protein secreted by the stomach mucosaSpasmolytic polypeptide (SP) (TFF2), a protein of about 115 residues that inhibits gastrointestinal motility and gastric acid secretionIntestinal trefoil factor (ITF) (TFF3)Xenopus laevis stomach proteins xP1 and xP4Xenopus integumentary mucins A.1 (FIM-A.1 or preprospasmolysin) and C.1 (FIM-C.1), proteins which may be involved in defence against microbial infections by protecting the epithelia from the external environmentXenopus skin protein xp2 (or APEG)Zona pellucida sperm-binding protein B (ZP-B)Intestinal sucrase-isomaltase ( / ), a vertebrate membrane bound, multifunctional enzyme complex which hydrolyses sucrose, maltose and isomaltose Lysosomal alpha-glucosidase ( )
Short Name	P_trefoil_chordata