13C NMR chemical shifts can predict disulfide bond formation

The presence of disulfide bonds can be detected unambiguously only by X-ray crystallography, and otherwise must be inferred by chemical methods. In this study we demonstrate that ¹³C NMR chemical shifts are diagnostic of disulfide bond formation, and can discriminate between cysteine in the reduced (free) and oxidized (disulfide bonded) state. A database of cysteine ¹³C C and C chemical shifts was constructed from the BMRB and Sheffield databases, and published journals. Statistical analysis indicated that the C shift is extremely sensitive to the redox state, and can predict the disulfide-bonded state. Further, chemical shifts in both states occupy distinct clusters as a function of secondary structure in the C/C chemical shift map. On the basis of these results, we provide simple ground rules for predicting the redox state of cysteines; these rules could be used effectively in NMR structure determination, predicting new folds, and in protein folding studies.