Cysteine conformationally constrained

Conotoxins are small (10-30 amino acids), disulphide-rich, conformationally constrained peptides produced by marine mollusks such as cone snails. The fish-hunting snails, in particular Conus geographus, have been extensively studied. Depending upon the arrangement of disulphide bonds and the number of residues between cysteines, five or more classes of conotoxin can be structurally identified ... 

T. A., Levy, M. A. and Veber, D.F. (1998). Conformation-ally constrained 1,3-diamino ketones a series of potent inhibitors of the cysteine protease cathepsin K. /. Med. Chem. 41, 3563-3567. 

It is possible to constrain peptides by introducing two codons for cysteine in both sites of the random region. Constraining a peptide in its active conformation is an advantage, but if it is constrained into an incorrect conformation, binding to the target molecule can be prevented. Several peptides have been isolated from cyclic libraries. The screening of pools... 

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