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Resumen del póster presentado a la 9ª Jornada de Jóvenes Investigadores de Química y Física de Aragón, celebrada el 16 de diciembre de 2021 en la Universidad de Zaragoza.

Objectives Formate dehydrogenases (FDHs) are NAD(P)H-dependent enzymes that catalyse the reversible oxidation of formate to CO2. The main goal was to use directed evolution to obtain variants of the FDH fromChaetomium thermophilum(CtFDH) with enhanced reduction activity in the conversion of CO(2)into formic acid. Results Four libraries were constructed targeting five residues in the active site. We identified two variants (G93H/I94Y and R259C) with enhanced reduction activity which were characterised in the presence of both aqueous CO(2(g))and HCO3-. The A1 variant (G93H/I94Y) showed a 5.4-fold increase in catalytic efficiency (k(cat)/K-M) compared to that of the wild-type for HCO(3)(-)reduction. The improved biocatalysts were also applied as a coupled cofactor recycling system in the enantioselective oxidation of 4-phenyl-2-propanol catalysed by the alcohol dehydrogenase fromStreptomyces coelicolorA3 (ScADH). Conversions in these reactions increased from 56 to 91% when the A1 variant was used instead of wild-typeCtFDH. Conclusions Two variants presenting up to five-fold increase in catalytic efficiency andk(cat)were obtained and characterised. They constitute a promising enzymatic alternative for CO(2)utilization and will serve as scaffolds to be further developed in order to meet industrial requirements.

Reductive Aminases (RedAms) catalyze the asymmetric reductive amination of ketones with primary amines to give secondary amine products. RedAms have great potential for the synthesis of bioactive chiral amines, however, insights into their mechanism are currently limited. Comparative studies on reductive amination of cyclohexanone with allylamine in the presence of RedAms, imine reductases (IREDs) or NaBH3CN support the distinctive activity of RedAms in catalyzing both imine formation and reduction in the reaction. Structures of AtRedAm from Aspergillus terreus, in complex with NADPH and ketone and amine substrates, along with kinetic analysis of active-site mutants, reveal modes of substrate binding, the basis for the specificity of RedAms for reduction of imines over ketones, and the importance of domain flexibility in bringing the reactive participants together for the reaction. This information is used to propose a mechanism for their action and also to expand the substrate specificity of RedAms using protein engineering.

Over the next decades, with the growing concern of rising atmospheric carbon dioxide (CO2) levels, the importance of investigating new approaches for its reduction becomes crucial. Reclamation of CO2 for conversion into biofuels represents an alternative and attractive production method that has been studied in recent years, now with enzymatic methods gaining more attention. Formate dehydrogenases (FDHs) are NAD(P)H-dependent oxidoreductases that catalyze the conversion of formate into CO2 and have been extensively used for cofactor recycling in chemoenzymatic processes. A new FDH from Clostridium ljungdahlii (ClFDH) has been recently shown to possess activity in the reverse reaction: the mineralization of CO2 into formate. In this study, we show the successful homologous expression of ClFDH in Escherichia coli. Biochemical and kinetic characterization of the enzyme revealed that this homologue also demonstrates activity toward CO2 reduction. Structural analysis of the enzyme through homology modeling is also presented.

Chiral primary amines are important intermediates in the synthesis of pharmaceutical compounds. Fungal reductive aminases (RedAms) are NADPH-dependent dehydrogenases that catalyse reductive amination of a range of ketones with short-chain primary amines supplied in an equimolar ratio to give corresponding secondary amines. Herein we describe structural and biochemical characterisation as well as synthetic applications of two RedAms from Neosartorya spp. (NfRedAm and NfisRedAm) that display a distinctive activity amongst fungal RedAms, namely a superior ability to use ammonia as the amine partner. Using these enzymes, we demonstrate the synthesis of a broad range of primary amines, with conversions up to >97% and excellent enantiomeric excess. Temperature dependent studies showed that these homologues also possess greater thermal stability compared to other enzymes within this family. Their synthetic applicability is further demonstrated by the production of several primary and secondary amines with turnover numbers (TN) up to 14000 as well as continuous flow reactions, obtaining chiral amines such as (R)-2-aminohexane in space time yields up to 8.1 g L-1 h-1. The remarkable features of NfRedAm and NfisRedAm highlight their potential for wider synthetic application as well as expanding the biocatalytic toolbox available for chiral amine synthesis.