Folding kinetics of phage T4 thioredoxin.

The folding mechanism for bacteriophage T4 thioredoxin is best described by a four-state box mechanism, N----Uc----Ut----It----N, where N indicates native, Uc the unfolded form with the cis proline isomer, Ut unfolded with the trans proline isomer, and It a compact form with a trans proline isomer. Both manual mixing fluorescence and size-exclusion chromatography indicate that there is a cis-trans proline isomerization that is important to the folding pathway. Furthermore, the data suggest that the cis-trans isomerization can also occur in a compact nativelike state which is referred to as It. The slow phase seen in fluorescence seems to be monitoring the cis-trans isomerization in the compact form, not the isomerization which occurs in the denatured state.