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Native amine dehydrogenases offer sustainable access to chiral amines, so the search for scaffolds capable of converting more diverse carbonyl compounds is required to reach the full potential of this alternative to conventional synthetic reductive aminations. Here we report a multidisciplinary strategy combining bioinformatics, chemoinformatics and biocatalysis to extensively screen billions of sequences in silico and to efficiently find native amine dehydrogenases features using computational approaches. In this way, we achieve a comprehensive overview of the initial native amine dehydrogenase family, extending it from 2,011 to 17,959 sequences, and identify native amine dehydrogenases with non-reported substrate spectra, including hindered carbonyls and ethyl ketones, and accepting methylamine and cyclopropylamine as amine donor. We also present preliminary model-based structural information to inform the design of potential (R)-selective amine dehydrogenases, as native amine dehydrogenases are mostly (S)-selective. This integrated strategy paves the way for expanding the resource of other enzyme families and in highlighting enzymes with original features. Sustainable chemistry can benefit from biocatalysis, but a high diversity of enzymes is needed. Here, the authors screen billions of protein sequences to provide an overview of the native amine dehydrogenase family for amine synthesis. [ABSTRACT FROM AUTHOR]

The NADPH‐dependent imine reductase from Ajellomyces dermatitidis (AdRedAm) catalyzes the reductive amination of certain ketones with amine donors supplied in an equimolar ratio. The structure of AdRedAm has been determined in three forms. The first form, which belongs to space group P3121 and was refined to 2.01 Å resolution, features two molecules (one dimer) in the asymmetric unit in complex with the redox‐inactive cofactor NADPH4. The second form, which belongs to space group C21 and was refined to 1.73 Å resolution, has nine molecules (four and a half dimers) in the asymmetric unit, each complexed with NADP+. The third form, which belongs to space group P3121 and was refined to 1.52 Å resolution, has one molecule (one half‐dimer) in the asymmetric unit. This structure was again complexed with NADP+ and also with the substrate 2,2‐difluoroacetophenone. The different data sets permit the analysis of AdRedAm in different conformational states and also reveal the molecular basis of stereoselectivity in the transformation of fluorinated acetophenone substrates by the enzyme. [ABSTRACT FROM AUTHOR]

Native amine dehydrogenases (nat-AmDHs) catalyze the (S)-stereoselective reductive amination of various ketones and aldehydes in the presence of high concentrations of ammonia. Based on the structure of CfusAmDH from Cystobacter fuscus complexed with Nicotinamide adenine dinucleotide phosphate (NADP+) and cyclohexylamine, we previously hypothesized a mechanism involving the attack at the electrophilic carbon of the carbonyl by ammonia followed by delivery of the hydride from the reduced nicotinamide cofactor on the re-face of the prochiral ketone. The direct reduction of carbonyl substrates into the corresponding alcohols requires a similar active site architecture and was previously reported as a minor side reaction of some native amine dehydrogenases and variants. Here we describe the ketoreductase (KRED) activity of a set of native amine dehydrogenases and variants, which proved to be significant in the absence of ammonia in the reaction medium but negligible in its presence. Conducting this study on a large set of substrates revealed the heterogeneity of this secondary ketoreductase activity, which was dependent upon the enzyme/substrate pairs considered. In silico docking experiments permitted the identification of some relationships between ketoreductase activity and the structural features of the enzymes. Kinetic studies of MsmeAmDH highlighted the superior performance of this native amine dehydrogenases as a ketoreductase but also its very low activity towards the reverse reaction of alcohol oxidation. [ABSTRACT FROM AUTHOR]

Native Amine Dehydrogenases (nat‐AmDHs) are NAD(P)H‐enzymes performing reductive amination, mainly active towards small aliphatic aldehydes and cyclic ketones, due to active site volumes limited by the presence of several bulky amino acids. Herein, inspired by the diversity of residues at these positions among the family, we report the implementation of mutations F140A and W145A in CfusAmDH and their transposition in nine other members. Moderate to high conversions were obtained with substrates not accepted by the native enzymes, notably n‐alkylaldehydes (44.6 %–99.5 % for hexanal to nonanal) and n‐alkylketones (16.0 %–53.7 % for hexan‐2‐one to nonan‐2‐one) with retention of excellent (S)‐enantioselectivity (>99 % ee). Complementary to the reported (R)‐selective AmDHs, the promising mutant CfusAmDH−W145A was further characterized for its synthetic potential. Crystal structure resolution and molecular dynamics gave insights into the cofactor and substrate specificity and the whole structural dynamics, thus providing keys for mutagenesis work on this enzyme family. [ABSTRACT FROM AUTHOR]

The biocatalytic asymmetric synthesis of amines from carbonyl compounds and amine precursors presents an important advance in sustainable synthetic chemistry. Oxidoreductases (ORs) that catalyze the NAD(P)H‐dependent reductive amination of carbonyl compounds directly to amines using amine donors present advantages complementary to those of amine transaminases (ATAs) with respect to selectivity, stability and substrate scope. Indeed some ORs accept alkyl and aryl amines as reaction partners enabling access to chiral secondary amine products that are not directly accessible using ATAs. Moreover, superior atom economy can usually be achieved as no sacrificial amines are required as with ATAs. In recent years a number of ORs that apparently catalyze both imine formation and imine reduction in the reductive amination of carbonyls has been identified using structure informed protein engineering, sequence analysis from natural biodiversity and increasingly a mixture of both. In this review we summarize the development of such enzymes from the engineering of amino acid dehydrogenases (AADHs) and opine dehydrogenases (OpDHs) to become amine dehydrogenases (AmDHs), which are active toward ketones devoid of any requisite carboxylate and/or amine functions, through to the discovery of native AmDHs and reductive aminases (RedAms), and the engineering of all of these scaffolds for improved or altered activity. Structural and mechanistic studies have revealed similarities, but also differences in the determinants of substrate binding and mechanism in the enzymes. The survey reveals that a complementary approach to enzyme discovery that utilizes both natural genetic resources and engineering can be combined to deliver biocatalysts that have significant potential for the industrial synthesis of chiral amines. [ABSTRACT FROM AUTHOR]

Asymmetric reductive aminations are some of the most important reactions in the preparation of active pharmaceuticals, as chiral amines feature in many of the world's most important drugs. Although many enzymes have been applied to the synthesis of chiral amines, the development of reductive amination reactions that use enzymes is attractive, as it would permit the one-step transformation of readily available prochiral ketones into chiral amines of high optical purity. However, as most natural 'reductive aminase' activities operate on keto acids, and many are able to use only ammonia as the amine donor, there is considerable scope for the engineering of natural enzymes for the reductive amination of ketones, and also for the preparation of secondary amines using alkylamines as donors. This review summarises research into the development of NAD(P)H-dependent dehydrogenases for the reductive amination of ketones, including amino acid dehydrogenases (AADHs), natural amine dehydrogenases (AmDHs), opine dehydrogenases (OpDHs) and imine reductases (IREDs). In each case knowledge of the structure and mechanism of the enzyme class is addressed, with a further description of the engineering of those enzymes for the reductive amination of ketones towards primary and also secondary amine products. [ABSTRACT FROM AUTHOR]

Molecular dynamics, native amine dehydrogenases, protein engineering, reductive amination, structural biodiversity Keywords: molecular dynamics; native amine dehydrogenases; protein engineering; reductive amination; structural biodiversity EN molecular dynamics native amine dehydrogenases protein engineering reductive amination structural biodiversity 1 1 1 11/24/22 20221122 NES 221122 B The Cover Feature b shows the active site of an amine dehydrogenase (AmDH), an enzyme which catalyzes the transformation of ketones into chiral amines. [Extracted from the article]

The front cover picture, provided by Mahima Sharma and Juan Mangas ‐ Sanchez, illustrates the enzymes (AADHs, AmDHs, OpDHs and IREDs) that have been applied to date in reductive amination reactions, shown on a tree that may also bear other fruit in the form of further reductive aminase enzymes (RedAms) that are yet to be discovered or obtained through in vitro evolution. Details can be found in the review on pages 2011 – 2025 (M. Sharma, J. Mangas ‐ Sanchez, N. J. Turner, G. Grogan, Adv. Synth. Catal. 2017, 359, 2011 – 2025; DOI 10.1002/adsc.201700356). [ABSTRACT FROM AUTHOR]