The identification of a robust leucine dehydrogenase from a directed soil metagenome for efficient synthesis of L-2-aminobutyric acid

L-2-aminobutyric acid (L-2-ABA) is a chiral precursor for the synthesis of anti-epileptic drug levetiracetam and anti-tuberculosis drug ethambutol. Asymmetric synthesis of L-2-ABA by leucine dehydrogenases has been widely developed. However, the limitations of natural enzymes, such as poor stability, low catalytic efficiency, and inhibition of high-concentration substrates, limit large-scale applications. Herein, by directed screening of a metagenomic library from unnatural amino acid-enriched environments, a robust leucine dehydrogenase, TvLeuDH, was identified, which exhibited high substrate tolerance and excellent enzymatic activity towards 2-oxobutyric acid. In addition, TvLeuDH has strong affinity for NADH. Subsequently, a three-enzyme co-expression system containing L-threonine deaminase, TvLeuDH, and glucose dehydrogenase was established. By optimizing reaction conditions, 1.5 M L-threonine could be converted to L-2-ABA with a 99% molar conversion rate and a space-time yield of 51.5 g·L-1 ·h-1 . In this process, no external coenzyme was added. The robustness of TvLeuDH allowed the reaction to be performed without the addition of extra salt as the buffer, demonstrating the simplest reaction system currently reported. These unique properties for the efficient and environmentally friendly production of chiral amino acids make TvLeuDH a particularly promising candidate for industrial applications, which reveals the great potential of directed metagenomics for industrial biotechnology.

Biocatalytic routes to anti-viral agents and their synthetic intermediates

An assessment of biocatalytic strategies for the synthesis of anti-viral agents, offering guidelines for the development of sustainable production methods for a future COVID-19 remedy.

Dynamic kinetic resolution of Vince lactam catalyzed by γ-lactamases: a mini-review

γ-Lactamases are versatile enzymes used for enzymatic kinetic resolution of racemic Vince lactam (2-azabicyclo[2.2.1]hept-5-en-3-one) in the industry. Optically pure enantiomers and their hydrolytic products are widely employed as key chemical intermediates for developing a wide range of carbocyclic nucleoside medicines, including US FDA-approved drugs peramivir and abacavir. Owing to the broad applications in the healthcare industry, the resolution process of Vince lactam has witnessed tremendous progress during the past decades. Some of the most important advances are the enzymatic strategies involving γ-lactamases. The strong industrial demand drives the progress in various strategies for discovering novel biocatalysts. In the past few years, several new scientific breakthroughs, including the genome-mining strategy and elucidation of several crystal structures, boosted the research on γ-lactamases. So far, several families of γ-lactamases for resolution of Vince lactam have been discovered, and their number is continuously increasing. The purpose of this mini-review is to describe the discovery strategy and classification of these intriguing enzymes and to cover our current knowledge on their potential biological functions. Moreover, structural properties are described in addition to their possible catalytic mechanisms. Additionally, recent advances in the newest approaches, such as immobilization to increase stability, and other engineering efforts are introduced.

Construction of an organelle-like nanodevice via supramolecular self-assembly for robust biocatalysts

Background

When using the microbial cell factories for green manufacturing, several important issues need to be addressed such as how to maintain the stability of biocatalysts used in the bioprocess and how to improve the synthetic efficiency of the biological system. One strategy widely used during natural evolution is the creation of organelles which can be used for regional control. This kind of compartmentalization strategy has inspired the design of artificial organelle-like nanodevice for synthetic biology and “green chemistry”.

Results

Mimicking the natural concept of functional compartments, here we show that the engineered thermostable ketohydroxyglutarate aldolase from Thermotoga maritima could be developed as a general platform for nanoreactor design via supramolecular self-assembly. An industrial biocatalyst-(+)-γ-lactamase was selected as a model catalyst and successful encapsulated in the nanoreactor with high copies. These nanomaterials could easily be synthesized by Escherichia coli by heterologous expression and subsequently self-assembles into the target organelle-like nanoreactors both in vivo and in vitro. By probing their structural characteristics via transmission electronic microscopy and their catalytic activity under diverse conditions, we proved that these nanoreactors could confer a significant benefit to the cargo proteins. The encapsulated protein exhibits significantly improved stability under conditions such as in the presence of organic solvent or proteases, and shows better substrate tolerance than free enzyme.

Conclusions

Our biodesign strategy provides new methods to develop new catalytically active protein-nanoreactors and could easily be applied into other biocatalysts. These artificial organelles could have widely application in sustainable catalysis, synthetic biology and could significantly improve the performance of microbial cell factories.

Graphical Abstract

Electronic supplementary material

The online version of this article (10.1186/s12934-018-0873-3) contains supplementary material, which is available to authorized users.

Computational tools for enzyme improvement: why everyone can - and should - use them

This review presents computational methods that experimentalists can readily use to create smart libraries for enzyme engineering and to obtain insights into protein-substrate complexes. Computational tools have the reputation of being hard to use and inaccurate compared to experimental methods in enzyme engineering, yet they are essential to probe datasets of ever-increasing size and complexity. In recent years, bioinformatics groups have made a huge leap forward in providing user-friendly interfaces and accurate algorithms for experimentalists. These methods guide efficient experimental planning and allow the enzyme engineer to rationalize time and resources. Computational tools nevertheless face challenges in the realm of transient modern technology.