Acceleration of the folding of acylphosphatase by stabilization of local secondary structure

The addition of trifluoroethanol or hexafluoroisopropanol converts the appa rent two-state folding of acylphosphatase, a small alpha/beta protein, into a multistate mechanism where secondary structure accumulates significantly in the denatured state before folding to the native state. This results in a marked acceleration of folding as revealed by following the intrinsic fl uorescence and circular dichroism changes upon folding. The folding rate is at a maximum when the secondary-structure content of the denatured state c orresponds to that of the native state, while further stabilization of seco ndary structure decreases the folding rate. These findings indicate that st abilization of intermediate structure can either enhance or retard folding depending on its nature and content of native-like interactions.