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Several protein engineering approaches were combined to optimize the selectivity and activity of Vibrio fluvialis aminotransferase (Vfat) for the synthesis of (3S,5R)-ethyl 3-amino-5-methyloctanoate; a key intermediate in the synthesis of imagabalin, an advanced candidate for the treatment of generalized anxiety disorder. Starting from wild-type Vfat, which had extremely low activity catalyzing the desired reaction, we engineered an improved enzyme with a 60-fold increase in initial reaction velocity for transamination of (R)-ethyl 5-methyl 3-oxooctanoate to (3S,5R)-ethyl 3-amino-5-methyloctanoate. To achieve this, <450 variants were screened, which allowed accurate assessment of enzyme performance using a low-throughput ultra performance liquid chromatography assay. During the course of this work, crystal structures of Vfat wild type and an improved variant (Vfat variant r414) were solved and they are reported here for the first time. This work also provides insight into the critical residues for substrate specificity for the transamination of (R)-ethyl 5-methyl 3-oxooctanoate and structurally related β-ketoesters.

Reductive amination of carbonyl compounds constitutes one of the most efficient ways to rapidly construct chiral and achiral amine frameworks. Imine reductase (IRED) biocatalysts represent a versatile family of enzymes for amine synthesis through NADPH‐mediated imine reduction. The reductive aminases (RedAms) are a subfamily of IREDs that were recently shown to catalyze imine formation as well as imine reduction. Herein, a diverse library of novel enzymes were expressed and screened as cell‐free lysates for their ability to facilitate reductive amination to expand the known suite of biocatalysts for this transformation and to identify more enzymes with potential industrial applications. A range of ketones and amines were examined, and enzymes were identified that were capable of accepting benzylamine, pyrrolidine, ammonia, and aniline. Amine equivalents as low as 2.5 were employed to afford up to >99 % conversion, and for chiral products, up to >98 % ee could be achieved. Preparative‐scale reactions were conducted with low amine equivalents (1.5 or 2.0) of methylamine, allylamine, and pyrrolidine, achieving up to >99 % conversion and 76 % yield.

A major challenge in chemical synthesis is to develop catalytic systems that convert simple molecules to complex high-value products. Often these valuable compounds must be manufactured asymmetrically, as their biochemical properties can differ based on the chirality of the molecule. Of great interest are enantioenriched amine diastereomers, which are prevalent in pharmaceuticals and agrochemicals, 1 yet their preparation often relies on low-e ciency multi-step synthesis. 2 Herein, we report the discovery and characterisation of a multi-functional biocatalyst, which operates using a previously unreported conjugate reduction-reductive amination mechanism. This enzyme (pIR-120), identi ed within a metagenomic imine reductase (IRED) collection 3 and originating from an unclassi ed Pseudomonas species, possesses an unusual active site architecture that facilitates an amine-activated conjugate alkene reduction followed by reductive amination. This enzyme enables the coupling of a broad selection of α,β-unsaturated carbonyls with amines for the e cient preparation of enantioenriched amine diastereomers. Moreover, employing a racemic substrate partner or conjugated dienyl-ketone provides a means of controlling additional stereocentres using the single catalyst. Mechanistic and structural studies have been carried out to delineate the order of individual steps catalysed by pIR-120 which have led to a proposal for the overall catalytic cycle. This work shows that the IRED family can serve as a platform for facilitating the discovery of further enzymatic activities for application in synthetic biology and organic synthesis.

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Enzyme design is an important area of ongoing research with a broad range of applications in protein therapeutics, biocatalysis, bioengineering, and other biomedical areas; however, significant challenges exist in the design of enzymes to catalyze specific reactions of interest. Here, we develop a computational protocol using an approach that combines molecular dynamics, docking, and MM-GBSA scoring to predict the catalytic activity of enzyme variants. Our primary focuses are to understand the molecular basis of substrate recognition and binding in an S-stereoselective ω-aminotransferase (ω-AT), which naturally catalyzes the transamination of pyruvate into alanine, and to predict mutations that enhance the catalytic efficiency of the enzyme. The conversion of (R)-ethyl 5-methyl-3-oxooctanoate to (3S,5R)-ethyl 3-amino-5-methyloctanoate in the context of several ω-AT mutants was evaluated using the computational protocol developed in this work. We correctly identify the mutations that yield the greatest improvements in enzyme activity (20-60-fold improvement over wild type) and confirm that the computationally predicted structure of a highly active mutant reproduces key structural aspects of the variant, including side chain conformational changes, as determined by X-ray crystallography. Overall, the protocol developed here yields encouraging results and suggests that computational approaches can aid in the redesign of enzymes with improved catalytic efficiency.

Insects tend to feed on related hosts. The phylogenetic composition of host plant communities thus plays a prominent role in determining insect specialization, food web structure, and diversity. Previous studies showed a high preference of insect herbivores for congeneric and confamilial hosts suggesting that some levels of host plant relationships may play more prominent role that others. We aim to quantify the effects of host phylogeny on the structure of quantitative plant-herbivore food webs. Further, we identify specific patterns in three insect guilds with different life histories and discuss the role of host plant phylogeny in maintaining their diversity. We studied herbivore assemblages in three temperate forests in Japan and the Czech Republic. Sampling from a canopy crane, a cherry picker and felled trees allowed a complete census of plant-herbivore interactions within three 0·1 ha plots for leaf chewing larvae, miners, and gallers. We analyzed the effects of host phylogeny by comparing the observed food webs with randomized models of host selection. Larval leaf chewers exhibited high generality at all three sites, whereas gallers and miners were almost exclusively monophagous. Leaf chewer generality dropped rapidly when older host lineages (5-80 myr) were collated into a single lineage but only decreased slightly when the most closely related congeneric hosts were collated. This shows that leaf chewer generality has been maintained by feeding on confamilial hosts while only a few herbivores were shared between more distant plant lineages and, surprisingly, between some congeneric hosts. In contrast, miner and galler generality was maintained mainly by the terminal nodes of the host phylogeny and dropped immediately after collating congeneric hosts into single lineages. We show that not all levels of host plant phylogeny are equal in their effect on structuring plant-herbivore food webs. In the case of generalist guilds, it is the phylogeny of deeper plant lineages that drives the food web structure whereas the terminal relationships play minor roles. In contrast, the specialization and abundance of monophagous guilds are affected mainly by the terminal parts of the plant phylogeny and do not generally reflect deeper host phylogeny.

Biocatalytic retrosynthetic analysis of dibenz[c,e]azepines has highlighted the use of imine reductase (IRED) and ω-transaminase (ω-TA) biocatalysts to establish the key stereocentres of these molecules. Several enantiocomplementary IREDs were identified for the synthesis of (R)- and (S)-5-methyl-6,7-dihydro-5H-dibenz[c,e]azepine with excellent enantioselectivity, by reduction of the parent imines. Crystallographic evidence suggests that IREDs may be able to bind one conformer of the imine substrate such that, upon reduction, the major product conformer is generated directly. ω-TA biocatalysts were also successfully employed for the production of enantiopure 1-(2-bromophenyl)ethan-1-amine, thus enabling an orthogonal route for the installation of chirality into dibenz[c,e]azepine framework.