Protein thermal unfolding

What is the predominant secondary structure in unfolded proteins In thermally unfolded proteins, there appears to be no predominant secondary structure. Individual residue conformations are distributed over the Pn, a, and f regions that constitute energy minima for single residues in aqueous solution (Section II,B). Still, since there is increasing evidence that the Pn conformation is at the global minimum, Pn conformers must be the most abundant in this ensemble. Short Pn- and o -helices and /1-strands will be present, but will rarely exceed two or three residues in length. 

Why is this reconciliation important After all, a 6 M GuHCl solution hardly recapitulates the physiologically milieu, and proteins unfolded under more physiologically relevant conditions are often (though not always see Hoshino et al., 1997) much more compact than expected for an excluded-volume random coil. Still, the chemically or thermally... 

DSC in biochemistry is the study of the energetics of thermally induced protein unfolding [276]. 

Many other fluorophores are temperature-sensitive only when they are bound to macromolecules. Figure 10.16 shows the effect of temperature on the fluorescence intensity of native and guanidine unfolded AEDANS-RNase. Increasing the temperature from 10 to 30°C induces a decrease in fluorescence intensity for both protein states. The intensity decrease in native protein is more affected by temperature than the guanidine-unfolded protein. This thermal quenching is the consequence of rapid movements of the protein structure around the fluorescent probe. These movements occur during the lifetime of the excited state, and their rate is temperature-dependent. 

The calcium ion in a-LA plays a structural role in stabilizing the protein. The thermal stability of the calcium-bound form of a-LA increases more than 40 °C compared to that of the apo-form. At low pH (e.g. pH 2), a-LA releases the calcium ion and becomes partially unfolded (molten globule state). This partially unfolded protein loses its tertiary structure but retains its secondary structure. Other metals, such as manganese or magnesium, are able to compete with calcium at the same site with a similar stabilizing effect. However, the binding of zinc, which is proposed to bind at different locations, decreases a-LA stability. ... 

Protein denaturation can be caused by a large number of physical and chemical factors (for an overview, see for example Refs. 1-3). We shall focus here on thermal denaturation (in solution), since it is obviously of prime importance in food science and technology, and also for fundamental reasons of its direct links with the thermodynamics of protein unfolding. Interfacial denaturation will be treated more succinctly, for less information is available on it. 

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