Pressure is a fundamental thermodynamic parameter that affects the free energy of a system. Le Chatelier's principle dictates that a pressurized system will organize so as to minimize its volume. For macromolecules in solution, this often results in changes in molecular structure.
There are many biophysical experiments that are enabled by the HP-SAXS cell: HP causes most proteins to unfold. Pressure affects the tertiary structure by collapsing or water-filling of internal microcavities in the proteins, thereby inducing unfolding in ways that are distinct from chemically or thermally induced denaturation. Thus, study of pressure-induced denaturation provides new information on the thermodynamics of protein folding.
Nozomi Ando, while working on her Ph.D in Sol Gruner's group at Cornell University, devised a high pressure SAXS cell to enable experimental exploration of the effects of pressure on proteins in solution. (1)
Study of the effects of pressure on biomolecular systems is not just an esoteric exercise. Most of the volume of earth’s biosphere exists at pressures in excess of 100 bar. Moreover, application of pressure in the roughly 100 to 1000 bar range encountered in the biosphere is known to have numerous effects on biomolecular systems, including, for example, large changes in enzymatic reaction rates and viral infectivity. Relatively few of these effects are well understood. Investigations using HP-SAXS can lead to a better fundamental understanding of biomolecular systems and ultimately to biotechnological applications and therapeutic strategies for targeting biomolecules related to human diseases.
Reference: (1) Ando, N. et al., High hydrostatic pressure small-angle X-ray scattering cell for protein solution studies featuring diamond windows and disposable sample cells, J. Appl. Crystallogr. 41, 167 (2008).