Relationship between the native-state hydrogen exchange and the folding pathways of barnase.

The previous native-state hydrogen exchange experiment with barnase failed to detect any partially unfolded intermediate state which was contrary to the experimental results from kinetic deuterium hydrogen exchange pulse labeling and protein engineering studies. This has been taken to suggest that the native-state hydrogen exchange method cannot be used alone as an analytical tool to study the folding pathways of proteins. Here, we revisited the pulse labeling experiment with barnase and detected no stable folding intermediate. This finding allows a reconciliation of the native-state HX data and the folding pathway of barnase. Along with alternative theoretical interpretations for a curved chevron plot of protein folding, these data suggest that further investigation of the nature of the intermediate of barnase is needed.