Refolding kinetic model

Scheme II. Kinetic model for the slow-refolding reactions of RNase T1 under strongly native conditions, U stands for unfolded species, I for intermediates of refolding, and N is the native protein. The superscript and the subscript indicate the isomeric states of Pro39 and Pro55, respectively, in the correct, nativelike cis (c) and in the incorrect, nonnative trans (t) isomeric state. As an example, 155 stands for an intermediate with Pro55 in the correct cis and Pro39 in the incorrect trans state. The time constants given for the individual steps refer to folding conditions of 0.15 M GdmCl, 0.1 M Tris-HCl, pH 8.0, at 10°C. From Kiefhaber et al. (1990b,c).

Once this domain is removed, refolding of the three collagen polypeptides to the correctly staggered molecules is very difficult or impossible. The folding reaction from three polypeptides into a triple helix is affected by the concentration of the peptides. For the kinetic refolding analysis of triple helical model... 

Fig. 7. Conservation of the unfolding/folding mechanism of cold-shock proteins (Csp) from B. subtilis (Bs), B. caldolyticus (fid), and Thermotoga maritima (Tm). (a) Equilibrium unfolding transitions of Csp from Bs (A), Be ( ), and Tm ( ) induced by GdmCI at 25° and monitored by intrinsic fluorescence. Least-squares fit analyses based on the two-state model yield stabilization energies AGstab = 11.3,20.1, and 26.2 kJ/mol for Csp from Bs, Be, and Tm, respectively, (b) Kinetics of unfolding (open symbols) and refolding (closed symbols) of Bs (A, A), Be ( , ) and T Csp (O, ), respectively. The apparent rate constants, X, are plotted against the GdmCI concentration. The fits are on the basis of the linear two-state model. ...

The sequence studied consists of M = 23 monomers, of which four represent C sites. The native conformation corresponds to [2-15 9-22] (Fig. 8a). The model sequence has six possible single and two disulfide intermediates including the native state. There are three native intermediates and two non-native intermediates. Even though the number of such intermediates are far less than the corresponding number in BPTI, it is sufficient to examine the cmcial distinction between the roles played by native and non-native intermediates in the folding kinetics. Some of the questions that arise in the experimental studies of refolding of BPTI can be precisely answered using these simple models. 

The results from studies of the kinetics of refolding of various oligomeric proteins are summarized in Table 11.1. Also listed are the kinetic constants for renaturation of the different enzymes studied by Jaenicke and co-workers as well as the activity of the monomeric unit (if any) fitting with the irreversible unimolecular-bimolecular model (Jaenicke, 1979 Jaenicke and Rudolph, 1980). 

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