Classification of Protein Disulfide Bonds.

Protein disulfide bonds are the links between pairs of cysteine residues in the polypeptide chain. These bonds are classified based on the sign of the five dihedral angles that define the cystine residue. Twenty disulfide configurations are possible using this convention and all 20 are represented in protein structures. Force distribution analysis of the pairwise forces between the cysteine residues of the different configurations identified two of the 20 as having significant strain: the -RHstaple and -/+RHhook disulfide bonds. These two disulfide configurations are associated with allosteric function in proteins. An online tool is available that provides a comprehensive analysis of protein disulfide bonds in Protein Data Bank structures, including configuration, strain energy, and solvent accessibility.