Unfolding rates mechanism

The molecular mechanisms by which the extension of the N-terminus by the extra methionine residue destabilized recombinant a-lactalbumin remain unclear. Additional conformational entropy of the extra methionine residue in the unfolded state could account for the destabilization and unfolding-rate acceleration of the recombinant protein [22]. Ishikawa and coworkers reported the destabilization of recombinant bovine a-lactalbumin, similarly induced by the extra N-terminal methionine residue, and showed that the enthalpy change of thermal unfolding was the same for the authentic and recombinant proteins, indicating that the destabilization was caused by an entropic effect [42]. However, the destabilization by the extra methionine residue in the lysozyme homologous to a-lactalbumin was rather enthalpic and accompanied by a disruption of hydrogen-bond networks in the N-terminal region [43,44]. 

In the presence of SDS, the unfolding rate accelerates and can be measured at lower temperature. SDS inhibits the refolding of the 7 species back to the native. There is no detectable aggregation in SDS and the transformation from N to 7 and then to M is quantitative. The unfolding mechanism of tailspike protein... 

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. ...

Isotope patterns produced by EXl mechanism can be recognized by peak width analysis [39]. The majority of proteins display EX2 mechanism in native conditions. However, EXl can often be achieved by either increasing (e.g., higher pH) or decreasing (e.g., adding denaturant to destabilize the folded stracture). EXl phenomenon is particularly valuable in the study of protein dynamics because the local unfolding rate can be determined directly from the spectra of deuterated... 

An example of this effect is provided by ribonuclease A (RNase A). At pH 8 and 37°, the rate of deamidation of Asn67 was more than 30-fold lower in the native than in the unfolded protein [111]. Deamidation of the native RNase A was also ca. 30-fold slower than of an octapeptide whose sequence is similar to that of the deamidation site, although the reaction mechanisms were similar [108][123],... 

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