Unperturbed dimensions of disordered proteins containing an interchain disulfide cross-link

Mean-square unperturbed radii of gyration, (s2)0, have been calculated for several proteins cross-linked via an interchain disulfide bond. Thirty different polypeptide chains were used. Characteristic ratios tend to be smaller for cross-linked proteins than for the uncross-linked chains, although exceptions to this generalization do exist. Random flight statistics tend to overestimate the value of g, defined as the ratio of (s2)0 for the cross-linked protein to (s2)0 for analogous linear polypeptide chain containing the same number of amino acid residues. The parameter fi, defined as the ratio of the (s2)0 for the ith uncross-linked polypeptide chain and the cross-linked protein, is usually more accurately estimated by random flight statistics than is g. When the cross-link connects two chains of identical amino acid sequence, the values of fi obtained via random flight statistics are within 6% of those provided by rotational isomeric state theory.