Increased stability of alcohol oxidase under high hydrostatic pressure

Stabilization of galactose oxidase by high hydrostatic pressure: Insights on the role of cavities size

High hydrostatic pressure stabilized galactose oxidase (GaOx) at 70.0-80.0°C against thermal inactivation. The pseudo-first-order rate constant of inactivation kinact decreased by a factor of 8 at 80°C and by a factor of 44 at 72.5°C. The most pronounced effect of pressure was at the lowest studied temperature of 70.0°C with an activation volume of inactivation ΔV‡ of 78.8 cm3 mol-1. The optimal pressure against thermal inactivation was between 200 and 300 MPa. Unlike other enzymes, as temperature increased the ΔV‡ of inactivation decreased, and as pressure increased the activation energy of inactivation Eai increased. Combining the results for GaOx with earlier research on the pressure-induced stabilization of other enzymes suggests that ΔV‡ of inactivation correlates with the total molar volume of cavities larger than ~100 Å3 in enzyme monomers for enzymes near the optimal pH and whose thermal unfolding is not accompanied by oligomer dissociation.

Alternative design strategies to help build the enzymatic retrosynthesis toolbox

Most of the complex molecules found in nature still cannot be synthesized by current organic chemistry methods. Given the number of enzymes that exist in nature and the incredible potential of directed evolution, the field of synthetic biology contains perhaps all the necessary building blocks to bring about the realization of applied enzymatic retrosynthesis. Current thinking anticipates that enzymatic retrosynthesis will be implemented using conventional cell-based synthetic biology approaches where requisite native, heterologous, designer, and evolved enzymes making up a given multi-enzyme pathway are hosted by chassis organisms to carry out designer synthesis. In this perspective, we suggest that such an effort should not be limited by solely exploiting living cells and enzyme evolution and describe some useful yet less intensive complementary approaches that may prove especially productive in this grand scheme. By decoupling reactions from the environment of a living cell, a significantly larger portion of potential synthetic chemical space becomes available for exploration; most of this area is currently unavailable to cell-based approaches due to toxicity issues. In contrast, in a cell-free reaction a variety of classical enzymatic approaches can be exploited to improve performance and explore and understand a given enzyme's substrate specificity and catalytic profile towards non-natural substrates. We expect these studies will reveal unique enzymatic capabilities that are not accessible in living cells.

Production of Aldehydes by Biocatalysis

The production of aldehydes, highly reactive and toxic chemicals, brings specific challenges to biocatalytic processes. Absence of natural accumulation of aldehydes in microorganisms has led to a combination of in vitro and in vivo strategies for both, bulk and fine production. Advances in genetic and metabolic engineering and implementation of computational techniques led to the production of various enzymes with special requirements. Cofactor synthesis, post-translational modifications and structure engineering are applied to prepare active enzymes for one-step or cascade reactions. This review presents the highlights in biocatalytical production of aldehydes with the potential to shape future industrial applications.

Increased activity of alcohol oxidase at high hydrostatic pressure

Alcohol oxidase (AOx) from P. pastoris has potential applications in the production of carbonyl compounds and for the detection and quantification of alcohols. However, AOx's poor stability and low activity have hindered its practical application. There are two fractions of AOx in P. pastoris with different thermal stability. High hydrostatic pressure (HHP) increased the activity of the labile (L) + resistant (R) combined fractions but not of the R fraction alone. The activity of the L + R fractions increased 2.4-fold at 160 MPa and 30 °C compared to the activity at 0.1 MPa. At higher temperatures, the increase in activity with pressure was greater due to the combined stabilization and activation effects. The reaction rate of the R fraction at 50 °C was 17.9 ± 3.6 or 17.7 ± 0.8 μM min^-1 at 80 or 160 MPa, respectively, and was not significantly different from the activity of the L + R fractions under the same conditions (18.4 ± 2.7 μM min^-1). The activation energy of the R fraction was not significantly different between 80 MPa (41.5 ± 10.5 kJ mol^-1) and 160 MPa (43.8 ± 7.8 kJ mol^-1). The combined increase in the stability of the R fraction at HHP enables the use of the enzyme at 50 °C with little loss of activity and an increased catalytic rate.