Barnase folding intermediate

Barnase was used in the last chapter to exemplify the basic kinetics of multistate reactions. Barnase has only one observable step for refolding, consisting of first-order kinetics (ty2 30 ms) from a folding intermediate that is the major stable species under conditions that favor folding (equation 19.1). 

The early stages of folding of barstar have been measured on the microsecond time scale by temperature jumping its cold-denatured state from 2 to 10°C.65,66 There is the fast formation of a folding intermediate (tm 200 fxs) with the peptidy 1-proline 48 bond trans, followed by the formation with ty2 60 ms of a second intermediate that is highly native-like because it binds to and inhibits barnase. The native-like intermediate then undergoes trans cis peptidyl-proline isomerization on the time scale of minutes to give the final native structure (equation 19.2). 

To search for folding intermediates, Khan et al. have examined the folding and unfolding kinetics of wild-type barnase and four mutants . These data combined with direct structural observations and simulation support a minimal reaction pathway for the folding of barnase that involves two detectable folding... 

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