| Cystine-knot domain | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Structure of human chorionic gonadotropin.[1] | |||||||||
| Identifiers | |||||||||
| Symbol | Cys_knot | ||||||||
| Pfam | PF00007 | ||||||||
| Pfam clan | CL0079 | ||||||||
| InterPro | IPR006208 | ||||||||
| SCOP | 1hcn | ||||||||
|
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A cystine knot is a protein structural motif where two disulfide bridges (cystines - formed from pairs of cysteine molecules) are formed. The sections of polypeptide that occur between them then form a loop through which a third disulfide bond passes, forming a rotaxane substructure. It occurs in many proteins across many species and provides considerable structural stability.[2]
This motif was first observed in the structure of Nerve Growth Factor, solved by X-ray crystallography and published in 1991 by Tom Blundell in Nature.[3]