The barriers in protein folding.

Elimination of an interaction which forms in denatured cytochrome c enables the majority of the molecules to fold to the native state on a 15 ms time scale, without populating observable intermediates. These results are contrary to the current view that particular steps in protein folding, including the supposedly rate-limiting molten globule to native transition, are intrinsically slow. Instead it appears that intermediates characterized so far may be kinetically trapped by barriers that are optional rather than integral to the folding process. Major barriers may result from misorganization of the chain in the initial condensation step.