PD

P or trefoil or TFF domain
PD
SMART accession number:SM00018
Description: Proposed role in renewal and pathology of mucous epithelia.
Interpro abstract (IPR000519):

A cysteine-rich domain of approximately forty five amino-acid residues has been found in some extracellular eukaryotic proteins [(PUBMED:7820556), (PUBMED:9187350), (PUBMED:8518738), (PUBMED:8267796)]. 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 beta-sheet, which is capped by an irregular loop and forms a central hairpin (loop 3). The beta-sheet is preceded by a short alpha-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 [(PUBMED:7820556), (PUBMED:8518738), (PUBMED:8267796)], including:

  • protein pS2 (TFF1), a protein secreted by the stomach mucosa
  • spasmolytic polypeptide (SP) (TFF2), a protein of about 115 residues that inhibits gastrointestinal motility and gastric acid secretion
  • intestinal trefoil factor (ITF) (TFF3)
  • Xenopus laevis stomach proteins xP1 and xP4
  • xenopus 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 environment
  • xenopus skin protein xp2 (or APEG)
  • Zona pellucida sperm-binding protein B (ZP-B)
  • intestinal sucrase-isomaltase (EC 3.2.1.48 / EC 3.2.1.10), a vertebrate membrane bound, multifunctional enzyme complex which hydrolyses sucrose, maltose and isomaltose
  • lysosomal alpha-glucosidase (EC 3.2.1.20)

Family alignment:
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There are 1230 PD domains in 822 proteins in SMART's nrdb database.

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