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Fatty aldehydes (FALs) can be derived from fatty acids (FAs) and related compounds and are frequently used as flavors and fragrances. Although chemical methods have been conventionally used, their selective biotechnological production aiming at more efficient and eco-friendly synthetic routes is in demand. α-Dioxygenases (α-DOXs) are heme-dependent oxidative enzymes biologically involved in the initial step of plant FA α-oxidation during which molecular oxygen is incorporated into the Cα-position of a FA (Cn) to generate the intermediate FA hydroperoxide, which is subsequently converted into the shortened corresponding FAL (Cn-1). α-DOXs are promising biocatalysts for the flavor and fragrance industries, they do not require NAD(P)H as cofactors or redox partner proteins, and they have a broad substrate scope. Here, we highlight recent advances in the biocatalytic utilization of α-DOXs with emphasis on newly discovered cyanobacterial α-DOXs as well as analytical methods to measure α-DOX activity in vitro and in vivo.
Fast screening of enzyme variants is crucial for tailoring biocatalysts for the asymmetric synthesis of non-natural chiral chemicals, such as amines. However, most existing screening methods either are limited by the throughput or require specialized equipment. Herein, we report a simple, high-throughput, low-equipment dependent, and generally applicable growth selection system for engineering amine-forming or converting enzymes and apply it to improve biocatalysts belonging to three different enzyme classes. This results in (i) an amine transaminase variant with 110-fold increased specific activity for the asymmetric synthesis of the chiral amine intermediate of Linagliptin; (ii) a 270-fold improved monoamine oxidase to prepare the chiral amine intermediate of Cinacalcet by deracemization; and (iii) an ammonia lyase variant with a 26-fold increased activity in the asymmetric synthesis of a non-natural amino acid. Our growth selection system is adaptable to different enzyme classes, varying levels of enzyme activities, and thus a flexible tool for various stages of an engineering campaign.
p-Coumaric acid (p-CA) is a key precursor for the biosynthesis of flavonoids. Tyrosine ammonia lyases (TALs) specifically catalyze the synthesis of p-CA from l-tyrosine, which is a convenient enzymatic pathway. To explore novel and highly active TALs, a phylogenetic tree-building approach was conducted including 875 putative TALs and 46 putative phenylalanine/tyrosine ammonia lyases (PTALs). Among them, 5 TALs and 3 PTALs were successfully characterized and found to exhibit the proposed enzymatic activity. The TAL from Chryseobacterium luteum sp. nov (TALclu) has the highest affinity (Km=0.019 mm) and conversion efficiency (kcat/Km=1631 s−1 ⋅ mm−1) towards l-tyrosine. The reaction conditions for two purified enzymes and their E. coli recombinant cells were optimized and p-CA yields of 2.03 g/L after 8 hours by TALclu and 2.35 g/L after 24 h by TAL from Rivularia sp. PCC 7116 (TALrpc) in whole cells were achieved. These TALs are thus candidates for the construction of whole-cell systems to produce the flavonoid precursor p-CA.
Enzymes, the driving biocatalysts in living organisms, are typically not suited for large-scale industrial use. In the last decade, enzyme engineering has evolved into the key technology to design tailor-made enzymes for chemical and pharmaceutical applications. We highlight current trends in enzyme engineering and biocatalysis based on outstanding examples from the pharmaceutical industry.
Abstract
Enzyme activity data for biocatalytic applications are currently often not annotated with standardized conditions and terms. This makes it extremely hard to retrieve, compare, and reuse enzymatic data. With advances in the fields of artificial intelligence (AI) and machine learning (ML), the automated usability of data in the form of machine‐readable annotations will play a crucial role for their success. It is becoming increasingly easy to retrieve complex data sets and extract relevant information; however, standardized data readability is a current limitation. In this contribution, we outline an iterative approach to develop standardized terms and create semantic relations (ontologies) to achieve this highly desirable goal of improving the discoverability, accessibility, interoperability, and reuse of digital resources in the field of biocatalysis.
β-Glucosidases (Bgls) convert cellobiose and other soluble cello-oligomers into glucose and play important roles in fundamental biological processes, providing energy sources in living organisms. Bgls are essential terminal enzymes of cellulose degradation systems and attractive targets for lignocellulose-based biotechnological applications. Characterization of novel Bgls is important for broadening our knowledge of this enzyme class and can provide insights into its further applications. In this study, we report the biochemical and structural analysis of a Bgl from the hemicellulose-degrading thermophilic anaerobe Thermoanaerobacterium saccharolyticum (TsaBgl). TsaBgl exhibited its maximum hydrolase activity on p-nitrophenyl-β-d-glucopyranoside at pH 6.0 and 55 °C. The crystal structure of TsaBgl showed a single (β/α)8 TIM-barrel fold, and a β8-α14 loop, which is located around the substrate-binding pocket entrance, showing a unique conformation compared with other structurally known Bgls. A Tris molecule inhibited enzyme activity and was bound to the active site of TsaBgl coordinated by the catalytic residues Glu163 (proton donor) and Glu351 (nucleophile). Titration experiments showed that TsaBgl belongs to the glucose-tolerant Bgl family. The gatekeeper site of TsaBgl is similar to those of other glucose-tolerant Bgls, whereas Trp323 and Leu170, which are involved in glucose tolerance, show a unique configuration. Our results therefore improve our knowledge about the Tris-mediated inhibition and glucose tolerance of Bgl family members, which is essential for their industrial application.
Abstract
First Aid Kits are collections of the most important medical equipment required for quick medical assistance. Similarly, enzyme kits can provide a proficient, ready‐ and easy‐to‐use collection of biocatalysts that can be applied with high reproducibility. In this article, we illustrate how kits of oxyfunctionalisation enzymes could operate as synthetic ‘First Aid’ for chemists working on complex natural product total synthesis in an early‐ or late‐stage fashion, as well as in lead diversification in drug discovery processes. We reason that enzyme kits could catalyse the integration of biocatalysis into (synthetic) organic chemistry and describe how we envision their future application.
Polybutylene adipate terephthalate (PBAT) is a biodegradable alternative to polyethylene and can be broadly used in various applications. These polymers can be degraded by hydrolases of terrestrial and aquatic origin. In a previous study, we identified tandem PETase-like hydrolases (Ples) from the marine microbial consortium I1 that were highly expressed when a PBAT blend was supplied as the only carbon source. In this study, the tandem Ples, Ple628 and Ple629, were recombinantly expressed and characterized. Both enzymes are mesophilic and active on a wide range of oligomers. The activities of the Ples differed greatly when model substrates, PBAT-modified polymers or PET nanoparticles were supplied. Ple629 was always more active than Ple628. Crystal structures of Ple628 and Ple629 revealed a structural similarity to other PETases and can be classified as member of the PETases IIa subclass, α/β hydrolase superfamily. Our results show that the predicted functions of Ple628 and Ple629 agree with the bioinformatic predictions, and these enzymes play a significant role in the plastic degradation by the consortium.
Abstract
Chiral and enantiopure amines can be produced by enantioselective transaminases via kinetic resolution of amine racemates. This transamination reaction requires stoichiometric amounts of co‐substrate. A dual‐enzyme recycling system overcomes this limitation: l‐amino acid oxidases (LAAO) recycle the accumulating co‐product of (S)‐selective transaminases in the kinetic resolution of racemic amines to produce pure (R)‐amines. However, availability of suitable LAAOs is limited. Here we use the heterologously produced, highly active fungal hcLAAO4 with broad substrate spectrum. H2O2 as byproduct of hcLAAO4 is detoxified by a catalase. The final system allows using sub‐stoichiometric amounts of 1 mol% of the transaminase co‐substrate as well as the initial application of l‐amino acids instead of α‐keto acids. With an optimized protocol, the synthetic potential of this kinetic resolution cascade was proven at the preparative scale (>90 mg) by the synthesis of highly enantiomerically pure (R)‐methylbenzylamine (>99 %ee) at complete conversion (50 %).
Abstract
The aldehyde tag is appropriate to selectively label proteins, prepare antibody‐drug conjugates or to immobilize enzymes or antibodies for biotechnological and medical applications. The cysteine within the consensus sequence CxPxR of the aldehyde tag is specifically oxidized by the formylglycine‐generating enzyme (FGE) to the non‐canonical and electrophilic amino acid Cα‐formylglycine (FGly). Subsequent reductive amination is a common method for site‐directed immobilization, which usually results in poor immobilization efficiency due to the reaction conditions. Here, we introduce a new solid support like agarose modified with an aryl substituted pyrazolone (Knoevenagel reagent) that was obtained in a facile and efficient 2‐step synthesis. The modified agarose allowed the site‐selective and efficient immobilization of aldehyde‐containing small molecules, peptides and proteins – in particular enzymes – at physiological pH (6.2–8.2) without any additive or catalyst needed. In comparison to reductive amination, higher loadings and activities were achieved in various buffers at different concentrations and temperatures.