Biocatalysis has become an important aspect of modern organic synthesis, both in academia and across the chemical and pharmaceutical industries. Its success has been largely due to a rapid expansion of the range of chemical reactions accessible, made possible by advanced tools for enzyme discovery coupled with high-throughput laboratory evolution techniques for biocatalyst optimization. A wide range of tailor-made enzymes with high efficiencies and selectivities can now be produced quickly and on a gram to kilogram scale, with dedicated databases and search tools aimed at making these biocatalysts accessible to a broader scientific community. This Primer discusses the current state-of-the-art methodology in the field, including route design, enzyme discovery, protein engineering and the implementation of biocatalysis in industry. We highlight recent advances, such as de novo design and directed evolution, and discuss parameters that make a good reproducible biocatalytic process for industry. The general concepts will be illustrated by recent examples of applications in academia and industry, including the development of multistep enzyme cascades.

Carboxylic acid reductase enzymes (CARs) meet the demand in synthetic chemistry for a green and regiospecific route to aldehydes from their respective carboxylic acids. However, relatively few of these enzymes have been characterized. A sequence alignment with members of the ANL (Acyl‐CoA synthetase/ NRPS adenylation domain/Luciferase) superfamily of enzymes shed light on CAR functional dynamics. Four unstudied enzymes were selected by using a phylogenetic analysis of known and hypothetical CARs, and for the first time, a thorough biochemical characterization was performed. Kinetic analysis of these enzymes with various substrates shows that they have a broad but similar substrate specificity. Electron‐rich acids are favored, which suggests that the first step in the proposed reaction mechanism, attack by the carboxylate on the α‐phosphate of adenosine triphosphate (ATP), is the step that determines the substrate specificity and reaction kinetics. The effects of pH and temperature provide a clear operational window for the use of these CARs, whereas an investigation of product inhibition by NADP+, adenosine monophosphate, and pyrophosphate indicates that the binding of substrates at the adenylation domain is ordered with ATP binding first. This study consolidates CARs as important and exciting enzymes in the toolbox for sustainable chemistry and provides specifications for their use as a biocatalyst.

As the enzyme toolbox for biocatalysis has expanded, so has the potential for the construction of powerful enzymatic cascades for efficient and selective synthesis of target molecules. Additionally, recent advances in computer-aided synthesis planning are revolutionising synthesis design in both synthetic biology and organic chemistry. However, the potential for biocatalysis is not well captured by tools currently available in either field. Here we present RetroBioCat, an intuitive and accessible tool for computer-aided design of biocatalytic cascades, freely available at retrobiocat.com . Our approach uses a set of expertly encoded reaction rules encompassing the enzyme toolbox for biocatalysis, and a system for identifying literature precedent for enzymes with the correct substrate specificity where this is available. Applying these rules for automated biocatalytic retrosynthesis, we show our tool to be capable of identifying promising biocatalytic pathways to target molecules, validated using a test-set of recent cascades described in the literature.

Carboxylic acid reductases (CARs) are biocatalysts of industrial importance. Their properties, especially their poor stability, render them sub-optimal for use in a bioindustrial pipeline. Here, we employed ancestral sequence reconstruction (ASR) – a burgeoning engineering tool that can identify stabilizing but enzymatically neutral mutations throughout a protein. We used a three-algorithm approach to reconstruct functional ancestors of the Mycobacterial and Nocardial CAR1 orthologues. Ancestral CARs (AncCARs) were confirmed to be CAR enzymes with a preference for aromatic carboxylic acids. Ancestors also showed varied tolerances to solvents, pH and in vivo-like salt concentrations. Compared to well-studied extant CARs, AncCARs had a Tm up to 35 °C higher, with half-lives up to nine times longer than the greatest previously observed. Using ancestral reconstruction we have expanded the existing CAR toolbox with three new thermostable CAR enzymes, providing access to the high temperature biosynthesis of aldehydes to drive new applications in biocatalysis.

Monoacylated diamines are common motifs present in pharmaceuticals, agrochemicals, and natural products. However, the synthesis of these compounds often requires selective protection/deprotection steps leading to waste and poor atom economy. Here we describe the truncation of a carboxylic acid reductase (CAR) yielding an adenylation domain capable of selective amide bond formation under aqueous conditions. This truncated construct had a higher amidation activity compared to the full-length enzyme. The amidation reaction is mediated by ATP, which can be recycled from polyphosphate using a class III polyphosphate kinase (CHU). The wide substrate scope and selectivity of this enzymatic amidation method were confirmed through the synthesis of 24 pharmaceutically relevant amides including building blocks of six active pharmaceutical ingredients (APIs). Moreover, up-scaling of selected examples, including two API’s, was achieved demonstrating the value of this approach for synthesis.

Abstract

Multi‐step enzyme reactions offer considerable cost and productivity benefits. Process models offer a route to understanding the complexity of these reactions, and allow for their optimization. Despite the increasing prevalence of multi‐step biotransformations, there are few examples of process models for enzyme reactions. From a toolbox of characterized enzyme parts, we demonstrate the construction of a process model for a seven enzyme, three step biotransformation using isolated enzymes. Enzymes for cofactor regeneration were employed to make this in vitro reaction economical. Good modelling practice was critical in evaluating the impact of approximations and experimental error. We show that the use and validation of process models was instrumental in realizing and removing process bottlenecks, identifying divergent behavior, and for the optimization of the entire reaction using a genetic algorithm. We validated the optimized reaction to demonstrate that complex multi‐step reactions with cofactor recycling involving at least seven enzymes can be reliably modelled and optimized.

Protein-based adhesives could have several advantages over petroleum-derived alternatives, including substantially lower toxicity, smaller environmental footprint, and renewable sourcing. Here, we report that non-covalently crosslinked bovine serum albumin and recombinant spider silk proteins have high adhesive strength on glass (8.53 and 6.28 MPa, respectively) and other transparent substrates. Moreover, the adhesives have high visible transparency and showed no apparent degradation over a period of several months. The mechanism of adhesion was investigated and primarily attributed to dehydration-induced reorganization of protein secondary structure, resulting in the supramolecular association of β-sheets into a densely hydrogen-bonded network.