Life as we know it is connected to liquid water. The chemistry of life is characterized by reactions of a limited number of biomolecules. Extreme conditions of a chemical nature are e.g. water activity, salinity, acidity, etc. In general organisms cope with these external conditions by maintaining normal internal conditions. Extreme conditions of a physical nature require different mechanisms.
Proteins can be denatured/unfolded by high hydrostatic pressure as well as by high and low temperatures. The observation that stability diagrams for bacteria, viruses and more complex systems are similar to those obtained for proteins suggests that proteins are the primary target in the inactivation of organisms.
The temperature-unfolding of proteins induces intermediates that show a strong tendency to form intermolecular aggregates. Because of its important role in a number of diseases, the mechanism of the formation of these aggregates gets closer attention. It turns out that pressure may be a good parameter to induce conformations of proteins that have a less stronger tendency for aggregation. This makes pressure an ideal tool to study the mechanism of fibril formation in detail.
Although pressure- as well as temperature-induced effects in biopolymers are closely connected with water, pressure-induced amorphization has been observed in inorganic substances, liquid crystals, synthetic polymers and starch. This gives some new directions for the interpretation of the observed effects in water-soluble biopolymers.
A good overview of these and other aspects may be found in contributions to a special issue on "Frontiers in High Pressure Biochemistry and Biophysics" edited by C. Balny et al. Biochem. Biophys. Acta (2002) 1595, 1-402.