Cystine knot

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Cystine-knot domain
PDB 1hcn EBI.jpg
Structure of human chorionic gonadotropin.[1]
Symbol Cys_knot
Pfam PF00007
Pfam clan CL0079
InterPro IPR006208
SCOP 1hcn

A cystine knot is a protein structural motif containing three disulfide bridges (formed from pairs of cysteine residues). The sections of polypeptide that occur between two of them 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] There are three types of cystine knot, which differ in the topology of the disulfide bonds:[3]

The growth factor cystine knot (GFCK) was first observed in the structure of Nerve Growth Factor, solved by X-ray crystallography and published in 1991 by Tom Blundell in Nature.[4] All GFCK structures that have been determined are dimeric, but their dimerization modes in different classes are different.[5]


  1. ^ Wu H, Lustbader JW, Liu Y, Canfield RE, Hendrickson WA (June 1994). "Structure of human chorionic gonadotropin at 2.6 A resolution from MAD analysis of the selenomethionyl protein". Structure. 2 (6): 545–58. PMID 7922031. doi:10.1016/s0969-2126(00)00054-x. 
  2. ^
  3. ^ Daly, N. L.; Craik, D. J. (2011). "Bioactive cystine knot proteins". Current Opinion in Chemical Biology. 15 (3): 362–368. PMID 21362584. doi:10.1016/j.cbpa.2011.02.008. 
  4. ^ PDB: 1bet​; McDonald NQ, Lapatto R, Murray-Rust J, Gunning J, Wlodawer A, Blundell TL (December 1991). "New protein fold revealed by a 2.3-A resolution crystal structure of nerve growth factor". Nature. 354 (6352): 411–4. PMID 1956407. doi:10.1038/354411a0. 
  5. ^ Jiang X, Dias JA, He X (Aug 2013). "Structural biology of glycoprotein hormones and their receptors: Insights to signaling". Mol Cell Endocrinol. 382 (1): 424–51. PMID 24001578. doi:10.1016/j.mce.2013.08.021.