Simultaneous enhancement of barley β-amylase thermostability and catalytic activity by R115 and T387 residue sites mutation

Strengthening core-region hydrogen-bond networks and rigidifying surface loop to enhance thermostability of an (R)-selective transaminase converting chiral hydroxyl amines

Transaminases have important applications in the synthesis of drug intermediates such as chiral amines. However, natural transaminases exhibit suboptimal thermal stability, limiting their further applications. Building upon an Rhodobacter sp.-derived (R)-selective transaminase (RbTA), we report a dual-region coupling engineering approach to improve thermostability of RbTA by strengthening the core hydrogen-bond networks and rigidifying the flexible surface loop. Through single strategy, we identified 4 thermostability improved single mutations, among which I249Q demonstrated the most substantial improvement, achieving a 18-fold increase in half-life (t1/240) and a 11.2 ℃ increase in T5010. Then in strategic coupling, the synergistic effect of dual-region modification was observed in both thermal stability and activity enhancement, as mutant with the best high-temperature catalytic performance, R136P/F228Y, had its T5010 improved by 7.1℃ and exhibited a 4.2-fold increase in kcat/Km towards (R)-3-amino-1-butanol. Finally, R136P/F228Y achieved a 20.5 % improvement in conversion over WT in an analytical-scale synthesis in 72 h at a 5 ℃ elevated catalytic temperature. Molecular dynamics simulations demonstrated that the synergy of the formation of new hydrogen bonds and decrease in flexibility accounted for the thermostability improvements. This study provides guidance for enhancing thermostability of similar fold-type enzymes without impairing enzymatic activity in an efficient manner.

Recent advances in simultaneous thermostability-activity improvement of industrial enzymes through structure modification

Engineered thermostable microbial enzymes are widely employed to catalyze chemical reactions in numerous industrial sectors. Although high thermostability is a prerequisite of industrial applications, enzyme activity is usually sacrificed during thermostability improvement. Therefore, it is vital to select the common and compatible strategies between thermostability and activity improvement to reduce mutants̕ libraries and screening time. Three functional protein engineering approaches, including directed evolution, rational design, and semi-rational design, are employed to manipulate protein structure on a genetic basis. From a structural standpoint, integrative strategies such as increasing substrate affinity; introducing electrostatic interaction; removing steric hindrance; increasing flexibility of the active site; N- and C-terminal engineering; and increasing intramolecular and intermolecular hydrophobic interactions are well-known to improve simultaneous activity and thermostability. The current review aims to analyze relevant strategies to improve thermostability and activity simultaneously to circumvent the thermostability and activity trade-off of industrial enzymes.