Effects of high hydrostatic pressure on Rhizopus chinensis lipase: II. Intermediate states during unfolding

Studying the effects of high pressure-temperature treatment on the structure and immunoreactivity of β-lactoglobulin using experimental and computational methods

The effects of high hydrostatic pressure (HHP) on the conformation and immunoreactivity of bovine β-lactoglobulin (BLG) were studied. BLG was treated under 100-600 MPa at the temperature of 20-60 °C. The immunoglobulin E (IgE) binding ability of BLG decreased when the pressure increased from 0.1 to 200 MPa. However, the IgE binding increased with the increase in pressure from 200 to 400 MPa, followed by a gradual decrease until a pressure of 600 MPa. The IgE binding ability continuously decreased with an increase in pressure at 60 °C. The conformation of HHP-treated BLG was evaluated using fluorescence spectroscopy, circular dichroism spectroscopy and molecular dynamics (MD) simulation. Increasing the temperature and pressure promoted the unfolding of BLG, causing the disappearance of some α-helixes and some β-sheets. Based on ELISA analysis, it was revealed that HHP-termperature treatment altered the immunoreactivity of BLG by altering the structures and conformational states of BLG.

Structural studies and molecular dynamic simulations of polyphenol oxidase treated by high pressure processing

High pressure processing (HPP) exhibited different effect on polyphenol oxidase (PPO), but the conformational changes was not clear yet. In this study, molecular dynamics simulation combined with spectroscopic experiments were used to explore PPO conformational changes under high pressure at the molecular level. The simulation results showed that high pressure decreased volume and hydrogen bonds, induced changes in active center and movement of loop. Especially, the conformational changes under 200 and above 400 MPa were different. Under 200 MPa, the distance between His 61 and Cu decreased by 0.4 Å, active pocket was exposed, substrate channel became larger. However, the distance increased by 6.1 Å under 600 MPa, active pocket moved inward, substrate channel became narrower. Docking results of 200 and 600 MPa had the highest and lowest binding affinity, whose T-score was 4.657 and 4.130, respectively. These results were consistent with spectroscopic experiments of PPO after HHP.

Protection effect of polyols on Rhizopus chinensis lipase counteracting the deactivation from high pressure and high temperature treatment

The influence of polyols on Rhizopus chinensis lipase (RCL) was investigated under high pressure. The poor stability of RCL was observed at 500 MPa at 60 °C without polyols which protected RCL against the loss of activity. The lipase is more stable in phosphate buffer than in tris buffer despite the protection of polyols. The activity was maintained 63% by the sorbitol of 2 mol/L in Tris-HCl buffer but 73% in phosphate buffer after the treatment at 500 MPa and 60 °C for 25 min. The same protective effects could be observed at 1 mol/L of sorbitol, erythritol, xylitol, and mannitol. However, further increase of hydroxyl group number could not significantly improve the enzyme stability. The protection of polyols on RCL appears to depend on both of the polyol nature and the hydroxyl group number. Together with fluorescence spectra, circular dichroism spectra indicated that the chaotic conformation of RCL under high pressure became more ordered with 1 mol/L sorbitol. The results showed that sorbitol effectively stabilized the lipase conformation including the hydrophobic core under extreme conditions. It might be attributed to the interaction of polyols with RCL surface to modify intra-/intermolecular hydrogen bonds, maintaining the hydrophobic interactions within RCL.

In situ high-pressure measurement of crystal solubility by using neutron diffraction

Crystal solubility is one of the most important thermo-physical properties and plays a key role in industrial applications, fundamental science, and geoscientific research. However, high-pressure in situ measurements of crystal solubility remain very challenging. Here, we present a method involving high-pressure neutron diffraction for making high-precision in situ measurements of crystal solubility as a function of pressure over a wide range of pressures. For these experiments, we designed a piston-cylinder cell with a large chamber volume for high-pressure neutron diffraction. The solution pressures are continuously monitored in situ based on the equation of state of the sample crystal. The solubility at a high pressure can be obtained by applying a Rietveld quantitative multiphase analysis. To evaluate the proposed method, we measured the high-pressure solubility of NaCl in water up to 610 MPa. At a low pressure, the results are consistent with the previous results measured ex situ. At a higher pressure, more reliable data could be provided by using an in situ high-pressure neutron diffraction method.