Kinetic role of early intermediates in protein folding

The traditional view that partly folded intermediates are important for directing a protein toward the native state has been challenged by the notion that proteins can intrinsically fold rapidly in a single step if kinetic complications due to slow conformational events are avoided. Intermediates that accumulate within the first few milliseconds of folding are, however, a common observation even for small single-domain proteins. Recent spectroscopic studies, coupled with quantitative kinetic analysis, suggest that folding is facilitated by the rapid formation of compact intermediates with some native-like structural features.