Hybrids of salicylalkylamides and Mannich bases: control of the amide conformation by hydrogen bonding in solution and in the solid state

N-terminal loops at the tetramer interface of nitrile hydratase act as "hooks" determining resistance to high amide concentrations

Nitrile hydratase (NHase) has been extensively utilized in industrial acrylamide production. However, the vulnerability to high concentrations of acrylamide limits its further application. Herein, we redesigned the N-terminal loop at the tetramer interface of a thermophilic NHase from Pseudonocardia thermophila JCM3095 (PtNHase), and its catalytic activity, resistance to high acrylamide concentrations, and thermostability were improved. Amino acid residues located in the N-terminal loop of the tetramer interface that are responsible for enhancing the resistance to high acrylamide concentrations were identified via static structural analysis and molecular dynamics simulations. A variant library was used to fine-tune the tetramer interface. Variant αL6T exhibited 3.5-fold greater resistance to 50% (v/v) acrylamide, whereas its activity was 1.2-fold higher than that of the wild-type (WT) enzyme, revealing no activity-stability trade-off. Compared to the use of Escherichia coli harboring the WT enzyme, the use of E. coli harboring αL6T increased the acrylamide concentration from 398.1 g/L to 500 g/L. Crystal structure-guided analysis of αL6T and molecular dynamics simulations revealed that increased enzyme surface hydration and the introduction of positive cross-correlation into the N-terminal loop of the tetramer interface caused the two loop regions to hook to each other, thus improving the resistance to high acrylamide concentrations.

Insight into the broadened substrate scope of nitrile hydratase by static and dynamic structure analysis

The narrow substrate scope limits the wide industrial application of enzymes. Here, we successfully broadened the substrate scope of a nitrile hydratase (NHase) through mutation of two tunnel entrance residues based on rational tunnel calculation. Two variants, with increased specific activity, especially toward bulky substrates, were obtained. Crystal structure analysis revealed that the mutations led to the expansion of the tunnel entrance, which might be conducive to substrate entry. More importantly, molecular dynamics simulations illustrated that the mutations introduced anti-correlated movements to the regions around the substrate tunnel and the active site, which would promote substrate access during the dynamic process of catalysis. Additionally, mutations on the corresponding tunnel entrance residues on other NHases also enhanced their activity toward bulky substrates. These results not only revealed that residues located at the enzyme surface were a key factor in enzyme catalytic performance, but also provided dynamic evidence for insight into enzyme substrate scope broadening.

Acidic and alkaline bimolecular hydrolysis of substituted formanilides. Computational analysis and modelling of substitution effects

In this article, the study of 67 compounds representing various para-, meta- and ortho- substituted formanilides is presented. These molecules and the products of their acidic and alkaline hydrolysis were studied using DFT quantum chemical methods in order to calculate the reaction enthalpies. These enthalpies are correlated with the hydrolysis rate constants, kH, published for the acid-catalysed acyl cleavage bimolecular (AAC2) mechanism and the modified base-catalysed acyl cleavage bimolecular (BAC2) mechanism. The found linear dependences can be used for the prediction of rate constants of non-synthesised formanilide derivatives.