A chemical method for investigating disulfide-coupled peptide and protein folding

Investigations of protein folding have largely involved studies using disulfide-containing proteins, as disulfide-coupled folding of proteins permits the folding intermediates to be trapped and their conformations determined. Over the last decade, a combination of new biotechnical and chemical methodology has resulted in a remarkable acceleration in our understanding of the mechanism of disulfide-coupled protein folding. In particular, expressed protein ligation, a combination of native chemical ligation and an intein-based approach, permits specifically labeled proteins to be easily produced for studies of protein folding using biophysical methods, such as NMR spectroscopy and X-ray crystallography. A method for regio-selective formation of disulfide bonds using chemical procedures has also been established. This strategy is particularly relevant for the study of disulfide-coupled protein folding, and provides us not only with the native conformation, but also the kinetically trapped topological isomer with native disulfide bonds. Here we review recent developments and applications of biotechnical and chemical methods to investigations of disulfide-coupled peptide and protein folding. Chemical additives designed to accelerate correct protein folding and to avoid non-specific aggregation are also discussed.