High-pressure SAXS, deep life, and extreme biophysics.

Abstract

The biological relevance of hydrostatic pressure is becoming much more widely understood and appreciated as discoveries of new niches for extreme life continue to emerge. The unusual chemistry and physiological adaptations of organisms under extreme pressure promises to be a rich source of new insights in the years ahead if structural information can be obtained at the molecular level. Fortunately, recent advances in instrumentation are making structural biology techniques easier to perform at extreme pressures and more widely available. In addition to biological applications, hydrostatic pressure is a useful biophysical tool that can perturb systems in ways directly connected to the presence of atomic-level voids, cavities, and other volumetric properties. Under pressure, individual molecular complexes can dissociate, and monomers can unfold; transitions can occur in lipid mesophases, and liquid phases can dissolve and re-form. Small angle X-ray solution scattering (SAXS) can detect and characterize pressure-induced changes in all these situations. This chapter reviews what is known about pressure effects in a wide variety of biomolecular systems and how those effects display in X-ray scattering data. The influence of hydrostatic pressure on solution scattering is discussed, and the most widely used data processing methods are re-examined considering pressure effects. The chapter concludes with an overview of the high-pressure SAXS instrument design followed by recommended data collection protocol.