Juxtaposed Half-Cystines as Disulphide Bridged Partners in Protein Tertiary Structure

Disulphide bridges involving juxtaposed half-cystines are observed in a number of protein three-dimensional structures analyzed from the Protein Data Bank. These disulphide bridges comprise a 'ring of 8-atoms' corresponding to Cα1-C'-N-Cα2-Cβ2-Sγ2-Sγ1-Cβ1-Cα1 in the two half-cystines. The presence of such disulphide bridges introduces a 'bend' or 'kink' in the protein polypeptide chain.