Pressure denaturation, unfolded proteins

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... 

Although very interesting biotranformations have been reported in supercritical carbon dioxide, this solvent has been found to affect enzyme activity adversely. CO can react reversibly with free amino groups (lysine residues, specifically) on the surface of the protein to form carbamates, leading to low activity enzyme. [21]. Furthermore, carbon dioxide dissolves in water at molar concentrations at moderate pressures (<100 bar) and rapidly forms H COj. This can create some problems in biocatalytic reactions because many enzymes are denatured (unfolded and/or deactivated) at low pH. Enzymes can also be denatured by pressurization/depressuriza-tion cycles. For all of them, it is necessary to develop new enzyme stabilization strategies. 

FlGURE 7.7 Combined effects of two variables on conformational stability of globular proteins, (a) Denaturation (unfolding) temperature as a function of pH for papain (P), lysozyme (L), cytochrome C (C), parvalbumin (A), and myoglobin (M). (b) Effect of concentration of guanidinium chloride concentration and temperature on conformation of lysozyme at pH 1.7. (c) Effect of pressure (1 kbar= 10s Pa) and temperature on conformation of chymotrypsinogen. (d) Effect of pressure and pH on conformation of myoglobin (20°C). 

The stabilizing (destabilizing) effect of pressure on the thermal denaturation of proteins has been associated with the presence (absence) of aggregation of the unfolded protein [79]. Intermolecular aggregation is indeed one of the most commonly observed effects of thermal denaturation. The temperature of unfolding may however be lowered considerably by a... 

At T = 300K, A ° = lOkcalmol. Applying about 10,000 atm of pressure can denature a protein at T = 300K. What is the volume change Av for the unfolding process ... 

Mechanical forces, such as shearing, shaking, and pressure, may also denature proteins [44,45], Shaking proteins may lead to inactivation owing to an increase in the area of the gas/liquid interface. At the interface, the protein unfolds and maximizes exposure of hydrophobic residues to the air. Surface denaturation may also occur at the protein/container interface and has been observed following adsorption of proteins to filter materials [46]. 

Turning now to the chapters in this volume, a variety of complementary techniques and approaches have been used to characterize peptide and protein unfolding induced by temperature, pressure, and solvent. Our goal has been to assemble these complementary views within a single volume in order to develop a more complete picture of denatured peptides and proteins. The unifying observation in common to all chapters is the detection of preferred backbone conformations in experimentally accessible unfolded states. 

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