Emerging strategies for expanding the toolbox of enzymes in biocatalysis

Abstract

Expanding the repertoire of reactions available to enzymes is an enduring challenge in biocatalysis. Owing to the synthetic versatility of transition metals, metalloenzymes have been favored targets for achieving new catalytic functions. Although less well explored, enzymes lacking metal centers can also be effective catalysts for non-natural reactions, providing access to reaction modalities that compliment those available to metals. By understanding how these activation modes can reveal new functions, strategies can be developed to access novel biocatalytic reactions. This review will cover discoveries in the last two years which access catalytic reactions that go beyond the native repertoire of metal-free biocatalysts.

Figure 1.

(a) Design and evolution of the artificial aldolase RA95.5–8F. Reactivity of the evolved enzyme (left) and the enzyme substrate interactions leading to enhanced reactivity (right).(b) Incorporation of a non-natural amino acid coupled with evolution leads to the creation of the novel esterase OE1.4. The unnatural amino acid facilitates hydrolysis of the acyl enzyme intermediate.

Figure 2.

(a) Merger of photocatalysis with non-natural lipase reactivity using wheat germ lipase (WGL). (b) Cyclohexanone Monooxygenase (CHMO) catalyzed ketone reduction. (c) ‘Ene’-reductase (YqjM) catalyzed reductive carbocyclization. (d) 4-oxalocrotonate tautomerase (4-OT) catalyzed coupling of nitromethane with Michael acceptors via an iminium intermediate.

Figure 3.

(a) ERED catalyzed radical dehalogenation using Gluconobacter oxydans ene-reductase (GluER). (b) Semiquinone enabled redox neutral radical cyclization with 12-oxophytodienoate reductase 1 (OPR1). (c) Photoinduced reductive cyclization with GluER. (d) Deacetoxylation via enzymatic redox activation using the NADPH dependent double bond reductase from Nicotiana tabacum (NtDBR).