Characterization of a New Marine Leucine Dehydrogenase from Pseudomonas balearica and Its Application for L-tert-Leucine Production

Leucine dehydrogenase (LeuDH) has emerged as the most promising biocatalyst for L-tert-leucine (L-Tle) production via asymmetric reduction in trimethylpyruvate (TMP). In this study, a new LeuDH named PbLeuDH from marine Pseudomonas balearica was heterologously over-expressed in Escherichia coli, followed by purification and characterization. PbLeuDH possessed a broad substrate scope, displaying activities toward numerous L-amino acids and α-keto acids. Notably, compared with those reported LeuDHs, PbLeuDH exhibited excellent catalytic efficiency for TMP with a Km value of 4.92 mM and a kcat/Km value of 24.49 s−1 mM−1. Subsequently, L-Tle efficient production was implemented from TMP by whole-cell biocatalysis using recombinant E. coli as a catalyst, which co-expressed PbLeuDH and glucose dehydrogenase (GDH). Ultimately, using a fed-batch feeding strategy, 273 mM (35.8 g L−1) L-Tle was achieved with a 96.1% yield and 2.39 g L−1 h−1 productivity. In summary, our research provides a competitive biocatalyst for L-Tle green biosynthesis and lays a solid foundation for the realization of large-scale L-Tle industrial production.

Novel Salt-Tolerant Leucine Dehydrogenase from Marine Pseudoalteromonas rubra DSM 6842

This study reported the cloning, expression, and characterization of a new salt-tolerant leucine dehydrogenase (PrLeuDH) from Pseudoalteromonas rubra DSM 6842. A codon-optimized 1038 bp gene encoding PrLeuDH was successfully expressed on pET-22b( +) in E. coli BL21(DE3). The purified recombinant PrLeuDH showed a single band of about 38.7 kDa on SDS-PAGE. It exhibited the maximum activity at 40 °C and pH 10.5, while kept high activities in the range of 25-45 °C and pH 9.5-12. The K_m value and turnover number k_cat for leucine of PrLeuDH were 2.23 ± 0.12 mM and 35.39 ± 0.05 s^-1, respectively, resulting in a catalytic efficiency k_cat/K_m of 15.87 s^-1/mM. Importantly, PrLeuDH remained 92.1 ± 2.67% active in the presence of 4.0 M NaCl. The study provides the first in-depth understanding of LeuDH from marine Pseudoalteromonas rubra, meanwhile the unique properties of high activity at low temperature and high salt tolerance make it a promising biocatalyst for the synthesis of non-protein amino acids and α-ketoacids under special conditions in pharmaceutical industry.

Industrial applications of cold-adapted enzymes: challenges, innovations and future perspective

Extreme cold environments are potential reservoirs of microorganisms producing unique and novel enzymes in response to environmental stress conditions. Such cold-adapted enzymes prove to be valuable tools in industrial biotechnology to meet the increasing demand for efficient biocatalysts. The inherent properties like high catalytic activity at low temperature, high specific activity and low activation energy make the cold-adapted enzymes well suited for application in various industries. The interest in this group of enzymes is expanding as they are the preferred alternatives to harsh chemical synthesis owing to their biodegradable and non-toxic nature. Irrespective of the multitude of applications, the use of cold-adapted enzymes at the industrial level is still limited. The current review presents the unique adaptive features and the role of cold-adapted enzymes in major industries like food, detergents, molecular biology and bioremediation. The review highlights the significance of omics technology i.e., metagenomics, metatranscriptomics and metaproteomics in enzyme bioprospection from extreme environments. It further points out the challenges in using cold-adapted enzymes at the industrial level and the innovations associated with novel enzyme prospection strategies. Documentations on cold-adapted enzymes and their applications are abundant; however, reports on the role of omics tools in exploring cold-adapted enzymes are still scarce. So, the review covers the aspect concerning the novel techniques for enzyme discovery from nature.

Enhanced catalytic efficiency and coenzyme affinity of leucine dehydrogenase by comprehensive screening strategy for L-tert-leucine synthesis

L-tert-leucine (L-Tle) is widely used as vital chiral intermediate for pharmaceuticals and as chiral auxiliarie for organocatalysis. L-Tle is generally prepared via the asymmetric reduction of trimethylpyruvate (TMP) catalyzed by NAD⁺-dependent leucine dehydrogenase (LeuDH). To improve the catalytic efficiency and coenzyme affinity of LeuDH from Bacillus cereus, mutation libraries constructed by error-prone PCR and iterative saturation mutation were screened by two kinds of high-throughput methods. Compared with the wild type, the affinity of the selected mutant E24V/E116V for TMP and NADH increased by 7.7- and 2.8-fold, respectively. And the k_cat/K_m of E24V/E116V on TMP was 5.4-fold higher than that of the wild type. A coupled reaction comprising LeuDH with glucose dehydrogenase of Bacillus amyloliquefaciens resulted in substrate inhibition at high TMP concentrations (0.5 M), which was overcome by batch-feeding of the TMP substrate. The total turnover number and specific space-time conversion of 0.57 M substrate increased to 11,400 and 22.8 mmol·h^-1·L^-1·g^-1, respectively. KEY POINTS: • The constructed new high-throughput screening strategy takes into account the two indicators of catalytic efficiency and coenzyme affinity. • A more efficient leucine dehydrogenase (LeuDH) mutant (E24V/E116V) was identified. • E24V/E116V has potential for the industrial synthesis of L-tert-leucine.

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.

Cloning and Expression of a Novel Leucine Dehydrogenase: Characterization and L-tert-Leucine Production

Among many genes encoding for amino acid dehydrogenase, a novel leucine dehydrogenase gene from Exiguobacterium sibiricum (EsiLeuDH) was isolated by using genome mining strategy. EsiLeuDH was overexpressed in Escherichia coli BL21 (DE3), followed by purification and characterization. The high thermostability of the enzyme confers its half-life up to 14.7 h at 50°C. Furthermore, the substrate specificity shows a broad spectrum, including many L-amino acids and aliphatic α-keto acids, especially some aryl α-keto acids. This enzyme coupled with recombinant formate dehydrogenase (FDH) was used to catalyze trimethylpyruvic acid (TMP) through reductive amination to generate enantiopure L-tert-leucine (L-Tle). In order to overcome the substrate inhibition effect, a fed-batch feeding strategy was adopted to transform up to 0.8 M of TMP to L-Tle, with an average conversion rate of 81% and L-Tle concentration of 65.6 g⋅L^–1. This study provides a highly efficient biocatalyst for the synthesis of L-Tle and lays the foundation for large-scale production and application of chiral non-natural amino acids.

Applications of Marine-Derived Microorganisms and Their Enzymes in Biocatalysis and Biotransformation, the Underexplored Potentials

Biodiversity has been explored in the search for novel enzymes, including forests, savannas, tundras, deserts, and finally the sea. Marine microorganisms and their enzymes are capable of being active in high-salt concentration, large range of temperature, and high incidence of light and pressure, constituting an important source of unique biocatalysts. This review presents studies employing whole-cell processes of marine bacteria and fungi, aiming for new catalysts for different reactions in organic synthesis, such as reduction, oxidation, hydroxylation, hydrolysis, elimination, and conjugation. Genomics and protein engineering studies were also approached, and reactions employing isolated enzymes from different classes (oxidoreductases, hydrolases, lyases, and ligases) were described and summarized. Future biotechnological studies and process development should focus on molecular biology for the obtention of enzymes with interesting, fascinating and enhanced properties, starting from the exploration of microorganisms from the marine environment. This review approaches the literature about the use of marine-derived bacteria, fungi, and their enzymes for biocatalytic reactions of organic compounds, promoting a discussion about the possibilities of these microorganisms in the synthesis of different substances.

A Novel Cold-Adapted Leucine Dehydrogenase from Antarctic Sea-Ice Bacterium Pseudoalteromonas sp. ANT178

l-tert-leucine and its derivatives are useful as pharmaceutical active ingredients, in which leucine dehydrogenase (LeuDH) is the key enzyme in their enzymatic conversions. In the present study, a novel cold-adapted LeuDH, psleudh, was cloned from psychrotrophic bacteria Pseudoalteromonas sp. ANT178, which was isolated from Antarctic sea-ice. Bioinformatics analysis of the gene psleudh showed that the gene was 1209 bp in length and coded for a 42.6 kDa protein containing 402 amino acids. PsLeuDH had conserved Phe binding site and NAD⁺ binding site, and belonged to a member of the Glu/Leu/Phe/Val dehydrogenase family. Homology modeling analysis results suggested that PsLeuDH exhibited more glycine residues, reduced proline residues, and arginine residues, which might be responsible for its catalytic efficiency at low temperature. The recombinant PsLeuDH (rPsLeuDH) was purified a major band with the high specific activity of 275.13 U/mg using a Ni-NTA affinity chromatography. The optimum temperature and pH for rPsLeuDH activity were 30 °C and pH 9.0, respectively. Importantly, rPsLeuDH retained at least 40% of its maximum activity even at 0 °C. Moreover, the activity of rPsLeuDH was the highest in the presence of 2.0 M NaCl. Substrate specificity and kinetic studies of rPsLeuDH demonstrated that l-leucine was the most suitable substrate, and the catalytic activity at low temperatures was ensured by maintaining a high k_cat value. The results of the current study would provide insight into Antarctic sea-ice bacterium LeuDH, and the unique properties of rPsLeuDH make it a promising candidate as a biocatalyst in medical and pharmaceutical industries.

Enzymatic asymmetric synthesis of chiral amino acids

This review summarizes the progress achieved in the enzymatic asymmetric synthesis of chiral amino acids from prochiral substrates.

Identification of catalysis, substrate, and coenzyme binding sites and improvement catalytic efficiency of formate dehydrogenase from Candida boidinii

Formate dehydrogenases (FDHs) are continually used for the cofactor regeneration in biocatalysis and biotransformation with hiring NAD(P)H-dependent oxidoreductases. Major weaknesses of most native FDHs are their low activity and operational stability in the catalytic reaction. In this work, the FDH from Candida boidinii (CboFDH) was engineered in order to gain an enzyme with high activity and better operational stability. Through comparing and analyzing its spatial structure with other FDHs, the catalysis, substrate, and coenzyme binding sites of the CboFDH were identified. To improve its performance, amino acids, which concentrated on the enzyme active site or in the conserved NAD(+) and substrate binding motif, were mutated. The mutant V120S had the highest catalytic efficiency (k cat/K m ) with COONH4 as it enhanced the catalytic velocity (k cat) and k cat/K m 3.48-fold and 1.60-fold, respectively, than that of the wild type. And, the double-mutant V120S-N187D had the highest k cat/K m with NAD(+) as it displayed an approximately 1.50-fold increase in k cat/K m . The mutants showed higher catalytic efficiency than other reported FDHs, suggesting that the mutation has achieved good results. The single and double mutants exhibited higher thermostability than the wild type. The structure-function relationship of single and double mutants was analyzed by homology models and site parsing. Asymmetric synthesis of L-tert-leucine was executed to evaluate the ability of cofactor regeneration of the mutants with about 100 % conversion rates. This work provides a helpful theoretical reference for the evolution of an enzyme in vitro and promotion of the industrial production of chiral compounds, e.g., amino acid and chiral amine.