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The cystine knot structural motif is present in peptides and
proteins from a variety of species, including fungi, okants,
marine molluscs, insects and spiders. It comprises an embedded
ring formed by two disulfide bonds and their connecting backbone
segments which is threaded by a third disulfide bond. It is
invariably associated with a nearby beta-sheet structure and
appears to be a highly efficient motif for structure
stabilization. Because of this stability, it makes an ideal
framework for molecular engineering applications. Peptides
containing this cystine knot are 26-48 residues long and include
ion channel blockers, haemolytic agents as well as molecules
having anitviral and antibacterial activities. The stability of
peptide toxins containing the cystine knot motif, their range of
bioactivities and their unique structural scaffold can be
harnessed for molecular engineering applications and in drug
design.
There are three classes of cystine knots: Growth Factor
Cystine Knot (GFCK), Inhibitor Cystine Knot (ICK) and the Cyclic
Cystine Knot (CCK). All are shown below.
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