Pathways & interactions
TB domain (IPR017878)
Short name: TB_dom
Overlapping homologous superfamilies
- TGF-beta binding (TB) domain superfamily (IPR036773)
The transforming growth factor beta family of cytokines, are potent and multifunctional signalling molecules. Prior to ligand receptor binding there exist extracellular regulators that target these cytokines and facilitate the formation of morphogen gradients that control developmental processes. Some of these proteins that are known to sequester latent TGF-beta contains a conserved domain, the TGF-beta binding (TB) domain.
The domain is characterised by 8 conserved cysteine residues, which include an unusual cysteine triplet [PMID: 9362480, PMID: 14607119]. The TB fold is globular with six beta-strands and two alpha-helices [PMID: 9362480, PMID: 14607119, PMID: 15062093]. The pairing of the eight cysteines is 1-3, 2-6, 4-7, and 5-8, creating a fairly rigid structure. In follistatin and in the first repeat of fibrillin and LTBPs the last disulphide bridge is absent.
Proteins containing a TB domain include:
- Vertebrate fibrillin-1, 2 and 3. Fibrillins form tissue-specific and temporally regulated microfibril networks. They are implicated in the regulation of TGF-beta signalling.
- Vertebrate latent TGF-beta binding proteins (LTBPs) 1, 2, 3 and 4 LTBPs regulate TGF-beta signalling by forming a latent complex with the cleaved TGF-beta proproteins.
- Vertebrate follistatin. It is an extracellular antagonist of various TGF-beta proteins. The TB domain of follistatin mimic a type I receptor of TGF-beta and binds TGF-beta which leads to the formation of a receptor-ligand-antagonist complex [PMID: 16198295].