RESUMEN
The cystine knot (CK) motif comprises an internal ring formed by two disulfide bonds and their connecting backbone segments which is threaded by a third disulfide bond .It is present in peptides and proteins of a variety of species ,in-cluding fungi ,plants ,marine molluscs ,insects and spiders .CK polypeptide is one of the ideal model molecules for drug design and molecular engineering research because of its stable structure and variety of bioactivities .Here we summarized the main structural features of both inhibitor cystine knot (ICK) peptide and cyclic cystine knot (CCK) peptide ,including primary se-quence ,topology ,permutation ,synthesis and folding characteristics ,as well as its applications on drug design and molecular engineering .