Equilibria of oligomeric proteins under high pressure - A theoretical description

High-pressure small-angle X-ray scattering cell for biological solutions and soft materials

Pressure is a fundamental thermodynamic parameter controlling the behavior of biological macromolecules. Pressure affects protein denaturation, kinetic parameters of enzymes, ligand binding, membrane permeability, ion trans-duction, expression of genetic information, viral infectivity, protein association and aggregation, and chemical processes. In many cases pressure alters the molecular shape. Small-angle X-ray scattering (SAXS) is a primary method to determine the shape and size of macromolecules. However, relatively few SAXS cells described in the literature are suitable for use at high pressures and with biological materials. Described here is a novel high-pressure SAXS sample cell that is suitable for general facility use by prioritization of ease of sample loading, temperature control, mechanical stability and X-ray background minimization. Cell operation at 14 keV is described, providing a q range of 0.01 < q < 0.7 Å-1, pressures of 0-400 MPa and an achievable temperature range of 0-80°C. The high-pressure SAXS cell has recently been commissioned on the ID7A beamline at the Cornell High Energy Synchrotron Source and is available to users on a peer-reviewed proposal basis.

Pressure tolerance of deep-sea enzymes can be evolved through increasing volume changes in protein transitions: a study with lactate dehydrogenases from abyssal and hadal fishes

We explore the principles of pressure tolerance in enzymes of deep-sea fishes using lactate dehydrogenases (LDH) as a case study. We compared the effects of pressure on the activities of LDH from hadal snailfishes Notoliparis kermadecensis and Pseudoliparis swirei with those from a shallow-adapted Liparis florae and an abyssal grenadier Coryphaenoides armatus. We then quantified the LDH content in muscle homogenates using mass-spectrometric determination of the LDH-specific conserved peptide LNLVQR. Existing theory suggests that adaptation to high pressure requires a decrease in volume changes in enzymatic catalysis. Accordingly, evolved pressure tolerance must be accompanied with an important reduction in the volume change associated with pressure-promoted alteration of enzymatic activity ( Δ V PP ∘ ). Our results suggest an important revision to this paradigm. Here, we describe an opposite effect of pressure adaptation-a substantial increase in the absolute value of Δ V PP ∘ in deep-living species compared to shallow-water counterparts. With this change, the enzyme activities in abyssal and hadal species do not substantially decrease their activity with pressure increasing up to 1-2 kbar, well beyond full-ocean depth pressures. In contrast, the activity of the enzyme from the tidepool snailfish, L. florae, decreases nearly linearly from 1 to 2500 bar. The increased tolerance of LDH activity to pressure comes at the expense of decreased catalytic efficiency, which is compensated with increased enzyme contents in high-pressure-adapted species. The newly discovered strategy is presumably used when the enzyme mechanism involves the formation of potentially unstable excited transient states associated with substantial changes in enzyme-solvent interactions.