Mycobacterium smegmatis acyltransferase: The big new player in biocatalysis

Comprehensive Review of EGCG Modification: Esterification Methods and Their Impacts on Biological Activities

Epigallocatechin gallate (EGCG), the key constituent of tea polyphenols, presents challenges in terms of its lipid solubility, stability, and bioavailability because of its polyhydroxy structure. Consequently, structural modifications are imperative to enhance its efficacy. This paper comprehensively reviews the esterification techniques applied to EGCG over the past two decades and their impacts on bioactivities. Both chemical and enzymatic esterification methods involve catalysts, solvents, and hydrophobic groups as critical factors. Although the chemical method is cost-efficient, it poses challenges in purification; on the other hand, the enzymatic approach offers improved selectivity and simplified purification processes. The biological functions of EGCG are inevitably influenced by the structural changes incurred through esterification. The antioxidant capacity of EGCG derivatives can be compromised under certain conditions by reducing hydroxyl groups, while enhancing lipid solubility and stability can strengthen their antiviral, antibacterial, and anticancer properties. Additionally, esterification broadens the utility of EGCG in food applications. This review provides critical insights into developing cost-effective and environmentally sustainable selective esterification methods, as well as emphasizes the elucidation of the bioactive mechanisms of EGCG derivatives to facilitate their widespread adoption in food processing, healthcare products, and pharmaceuticals.

Achieving cinnamic acid amides in water by a variant of acyltransferase from Mycobacterium smegmatis and its immobilized form using Ni-NTA modified aspen powder as a carrier

An aqueous N-acylation reaction for preparing cinnamic acid amides was realized by using a variant of acyltransferase from Mycobacterium smegmatis (MsAcT-L12A), whereas the wild-type MsAcT showed no activity. MsAcT-L12A exhibited broad substrate adaptability, and preferred the substrates with electron-donating group. When the vinyl cinnamate (1a, 40 mM) and p-methoxyaniline (2a, 4 mM) were involved in the reaction, the excellent yield reached to 86.7 % ± 2.1 % within 3 h by MsAcT-L12A (1 mgpro./mL) in a PBS buffer (100 mM, pH 8.0) at 25 °C. The aqueous N-acylation reaction could be further improved by using an immobilized MsAcT-L12A. The biomass aspen powder (AP) as a carrier provided a low-cost, green, and environmental-friendly immobilization strategy. After it was modified by Ni-NTA, the obtained Ni-NAP could realize one-step purification and immobilization of MsAcT-L12A. The accomplished MsAcT-L12A-Ni-NAP exhibited excellent stability and recyclability, and retained its relative yield as 83.3 % ± 2.2 % even after the 7th cycle of reuse. Using only PBS buffer as a reaction medium, the operation for MsAcT-L12A-catalyzed acyl transfer was greatly simplified, and the improved stabilities of MsAcT-L12A-Ni-NAP could enhance its application potential.

The Quantum Chemical Cluster Approach in Biocatalysis

ConspectusThe quantum chemical cluster approach has been used for modeling enzyme active sites and reaction mechanisms for more than two decades. In this methodology, a relatively small part of the enzyme around the active site is selected as a model, and quantum chemical methods, typically density functional theory, are used to calculate energies and other properties. The surrounding enzyme is modeled using implicit solvation and atom fixing techniques. Over the years, a large number of enzyme mechanisms have been solved using this method. The models have gradually become larger as a result of the faster computers, and new kinds of questions have been addressed. In this Account, we review how the cluster approach can be utilized in the field of biocatalysis. Examples from our recent work are chosen to illustrate various aspects of the methodology. The use of the cluster model to explore substrate binding is discussed first. It is emphasized that a comprehensive search is necessary in order to identify the lowest-energy binding mode(s). It is also argued that the best binding mode might not be the productive one, and the full reactions for a number of enzyme-substrate complexes have therefore to be considered to find the lowest-energy reaction pathway. Next, examples are given of how the cluster approach can help in the elucidation of detailed reaction mechanisms of biocatalytically interesting enzymes, and how this knowledge can be exploited to develop enzymes with new functions or to understand the reasons for lack of activity toward non-natural substrates. The enzymes discussed in this context are phenolic acid decarboxylase and metal-dependent decarboxylases from the amidohydrolase superfamily. Next, the application of the cluster approach in the investigation of enzymatic enantioselectivity is discussed. The reaction of strictosidine synthase is selected as a case study, where the cluster calculations could reproduce and rationalize the selectivities of both the natural and non-natural substrates. Finally, we discuss how the cluster approach can be used to guide the rational design of enzyme variants with improved activity and selectivity. Acyl transferase from Mycobacterium smegmatis serves as an instructive example here, for which the calculations could pinpoint the factors controlling the reaction specificity and enantioselectivity. The cases discussed in this Account highlight thus the value of the cluster approach as a tool in biocatalysis. It complements experiments and other computational techniques in this field and provides insights that can be used to understand existing enzymes and to develop new variants with tailored properties.

Mimicking Natural Metabolisms: Cell-Free Flow Preparation of Dopamine

The biosynthesis of dopamine (DA) from L-tyrosine as starting material is an excellent yet challenging strategy. Here we developed a versatile, multi-enzymatic platform for the biocatalytic preparation of DA in a continuous mode with excellent conversion (90 %) and reaction time (45 min). The system exploits the immobilization of a decarboxylase from Bacillus pumilis (Fdc) and a tyrosinase from Agaricus bisporus (Tyr), which were combined to mimic the in-vivo synthesis of DA (both primary and secondary metabolisms) giving rise to an efficient strategy with a considerable reduction of process associated costs and environmental impact. To enhance the system automation, an in-line purification via catch-and-release procedure was added.

Chemoenzymatic Synthesis of Optically Active Alcohols Possessing 1,2,3,4-Tetrahydroquinoline Moiety Employing Lipases or Variants of the Acyltransferase from Mycobacterium smegmatis

The enzymatic kinetic resolution (EKR) of racemic alcohols or esters is a broadly recognized methodology for the preparation of these compounds in optically active form. Although EKR approaches have been developed for the enantioselective transesterification of a vast number of secondary alcohols or hydrolysis of their respective esters, to date, there is no report of bio- or chemo-catalytic asymmetric synthesis of non-racemic alcohols possessing 1,2,3,4-tetrahydroquinoline moiety, which are valuable building blocks for the pharmaceutical industry. In this work, the kinetic resolution of a set of racemic 1,2,3,4-tetrahydroquinoline-propan-2-ols was successfully carried out in neat organic solvents (in the case of CAL-B and BCL) or in water (in the case of MsAcT single variants) using immobilized lipases from Candida antarctica type B (CAL-B) and Burkholderia cepacia (BCL) or engineered acyltransferase variants from Mycobacterium smegmatis (MsAcT) as the biocatalysts and vinyl acetate as irreversible acyl donor, yielding enantiomerically enriched (S)-alcohols and the corresponding (R)-acetates with E-values up to 328 and excellent optical purities (>99% ee). In general, higher ee-values were observed in the reactions catalyzed by lipases; however, the rates of the reactions were significantly better in the case of MsAcT-catalyzed enantioselective transesterifications. Interestingly, we have experimentally proved that enantiomerically enriched 1-(7-nitro-3,4-dihydroquinolin-1(2H)-yl)propan-2-ol undergoes spontaneous amplification of optical purity under achiral chromatographic conditions.

Process intensification in continuous flow biocatalysis by up and downstream processing strategies

In this review, we focus on the holistic continuous enzymatic production and put special emphasis on process intensification by up- and downstream processing in continuous flow biocatalysis. After a brief introduction, we provide an overview of current examples of enzyme immobilization as an upstream process for flow biocatalysis. Thereafter, we provide an overview of unit operations as downstream processing strategies, namely continuous (i) liquid-liquid extraction, (ii) adsorptive downstream processing, and (iii) crystallization and precipitation. Eventually, we present our perspectives on future trends in this research field.