CT

C-terminal cystine knot-like domain (CTCK)
CT
SMART accession number:SM00041
Description: The structures of transforming growth factor-beta (TGFbeta), nerve growth factor (NGF), platelet-derived growth factor (PDGF) and gonadotropin all form 2 highly twisted antiparallel pairs of beta-strands and contain three disulphide bonds. The domain is non-globular and little is conserved among these presumed homologues except for their cysteine residues. CT domains are predicted to form homodimers.
Interpro abstract (IPR006207): Four recent crystal structures of growth factors--nerve growth factor, transforming growth factor-beta, platelet-derived growth factor, and human chorionic gonadotropin--from four separate superfamilies revealed that these proteins are structurally related and share a common overall topology [(PUBMED:8490958)]. These proteins have very little sequence homology, but they all have an unusual arrangement of six cysteines linked to form a "cystine-knot" conformation. The active forms of these proteins are dimers, either homo- or heterodimers [(PUBMED:7663117)]. Because of their shape, there appears to be an intrinsic requirement for the cystine-knot growth factors to form dimers. This extra level of organisation increases the variety of structures built around this simple structural motif [(PUBMED:7583638)].
Family alignment:
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There are 746 CT domains in 746 proteins in SMART's nrdb database.

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