Pathways and mechanisms of protein folding.

The folding transitions of small globular proteins are cooperative, so partially-folded intermediates are unstable and usually not detectable at equilibrium. The kinetics of folding are usually complicated by slow cis-trans isomerisation of peptide bonds adjacent to Pro residues in the unfolded protein. Nevertheless, folding pathways may be elucidated experimentally using the disulphide interaction between Cys residues to trap the unstable intermediates. The pathways determined in this way are unexpectedly complex, probably as a result of the need to go through a high-energy distorted form of the native conformation.