Pressure induced unfolding

Because the molar volume of an unfolded protein is less than that of the native state, increasing pressure leads to denaturation (Gross and Jaenicke, 1994). Royer and co-workers have employed high-pressure SAXS to monitor the pressure-induced unfolding of Snase. They find that the unfolded ensemble achieves a pressure-independent Rg of... 

It is of particular interest to note that the temperature dependence of the pressure-induced unfolding and the urea-induced unfolding of proteins at ambient pressure give rise to negative activation energies, i.e. these processes go faster at lower temperatures. Bridgman already noted this effect and found it quite unexpected [1]. 

These mechanisms are consistent with the differences that have been observed between the temperature and pressure induced unfolding of proteins with various experimental approaches. 

Fig. 31. Denaturation pressure ( p ), volume change of pressure-induced unfolding (A T°), and standard Gibbs free energy change (AG ), extrapolated to 1 bar, for the pressure-induced tmfolding of SNase at different molar concentrations (c) of cosolvents.

Certain pressure-induced unfolding transitions are known to occur slowly. The time required for conformational equilibration after the application of pressure has been found to depend on the protein itself, on the temperature, and on other environmental parameters. Therefore, as a general rule, samples should be allowed to equilibrate under pressure for 12 h prior to electrophoresis. 

Panick, G., Winter, R. Pressure-induced unfolding/refolding of ribonuclease A static and kinetic Fourier transform infrared spectroscopy study, Biochem. 39 (2000) 1862-1869. 

Pressure induced unfolding studies are more rarely performed since a specialized high pressure cell is required. 

Pressure-induced unfolding In the relationship for pressure, P, induced unfolding of proteins, AG° is again the value of the free energy change at 1 atmosphere pressure and A F = Vu -Vn is the difference in volume... 

There are several reasons to measure the effect of pressure on a wide variety of thermodynamic systems. Perhaps the most important argument is that one can separate the effects of volume and thermal energy changes, which appear simultaneously in temperature experiments . Moreover, high pressure can induce unfolding of protein in a different way from thermal denaturation. The pressure studies have considerably increased in the last decades" . 

Meersman, F., Smeller, L., and Heremans, K. (2002) Comparative Fourier transform infrared spectroscopy of cold-, pressure-, and heat-induced unfolding and aggregation of myoglobin. Biophysical Journal 82, 2635-2644... 

In the urea-induced unfolding the binding of urea to the protein is exothermic at ambient pressure... 

Vidugiris, G. J. A. and Royer, C. A. 1998, Determination of the volume changes for pressure-induced transitions of apomyoglobin between the native, molten globule, and unfolded states. Biophysical Journal 75, 463-470. 

Sasahara, K., M. Sakurai, and K. Nitta. 2001. Pressure effect on denaturant-induced unfolding of hen egg white lysozyme. Proteins Structure, Function, and Genetics. 44, 180. 

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