FAST AND SLOW TRACKS IN LYSOZYME FOLDING - INSIGHT INTO THE ROLE OF DOMAINS IN THE FOLDING PROCESS

The folding of lysozyme involves parallel events in which hydrogen exc hange kinetics indicate the development of persistent structure at ver y different rates. We have monitored directly the kinetics of formatio n of the native molecule by the binding of a fluorescently labelled in hibitor, MeU-diNAG ylumbelliferyl-N,N'-diacetyl-beta-D-chitobioside). The data show that native character monitored in this way also develop s with different timescales. Although the rate determining step on the slow pathway (similar to 75% of molecules at pH 5.5, 20 degrees C) ca n be attributed to the need to reorganise structure formed early in th e folding process, the data indicate that the rate determining step on the fast track (involving similar to 25% of molecules) involves the d ocking of the two constituent domains of the protein. In the fast fold ing track the data are consistent with a model in which each domain fo rms persistent structure prier to their docking in a locally cooperati ve manner on a timescale comparable to the folding of small single dom ain proteins. (C) 1997 Academic Press Limited.