Nocathiacin I, a glycosylated thiopeptide antibiotic, displays excellent antibacterial activities against multidrug resistant bacterial pathogens. Previously, a novel nocathiacin I formulation for intravenous administration has been successfully developed and its aqueous solubility is greatly enhanced for clinical application. The purpose of the present study was to increase the fermentation titer of nocathiacin I and reduce or eliminate analogous impurities by screening the medium ingredients using response surface methodology. After a sysmatic optimization, a water-soluble medium containing quality-controllable components was developed and validated, resulting in an increase in the production of nocathiacin I from 150 to 405.8 mg·L−1 at 150-L scale. Meanwhile, the analogous impurities existed in reported processes were greatly reduced or eliminated. Using optimized medium for fermentation, nocathiacin I with pharmaceutically acceptable quality was easily obtained with a recovery of 67%. In conclusion, the results from the present study offer a practical and efficient fermentation process for the production of nocathiacin I as a therapeutic agent.

AbstractGlycosaminoglycans (GAG) lyases are useful biocatalysts for the preparation of oligosaccharides, but their substrate spectra are limited to the same family. Thus, the degradation activity across families of GAG lyases is advantageous and desirable for various applications. In this study, residue Lys130 at the substrate entrance of monomeric heparinase III from Pedobacter heparinus ATCC 13125 was replaced by cysteine, and the resulting mutant K130C showed novel catalytic activity in degrading hyaluronic acid without affecting its native activity toward heparin and heparan sulfate. The broadened catalytic promiscuity by mutant K130C was the result of dimerization through a disulfide bond to expand the substrate binding pocket. This bifunctional enzyme is potentially valuable in the degradation of different types of GAGs.

Nosiheptide and nocathiacin are thiopeptides within the same series with high similarity from chemical structure to organization of the biosynthetic gene cluster. Previously, NosB, a cytochrome P450-like enzyme, was demonstrated to be responsible for the hydroxylation of Glu-6 during nosiheptide maturation. Based on 64% amino acid sequence identity, NocB from Nocardia sp. ATCC 202099 is expected to exhibit a similar catalytic function to NosB. After replacing nosB by nocB in nosiheptide-producing Streptomyces actuosus ATCC 25421, NocB was proved to be a cytochrome P450-like monooxygenase responsible for the hydroxylation of Glu-6 at the γ-position in the biosyntheses of both nosiheptide and nocathiacin. Enzyme kinetics and structural difference between nosiheptide and nocathiacin further revealed that NocB is less active than NosB towards unglycosylated intermediate 3 containing a bicyclic core structure.

D-amino acids are widely distributed in living organisms and are suggested to play important roles in protein folding and function. Genetic incorporation of D-amino acids through protein synthesis machinery has been an exploratory task in protein engineering, and is greatly enticing but difficult. In the present work, a number of D-amino acids were genetically incorporated into green fluorescent protein using a polysubstrate-specific tRNA synthetase with cognate tRNA in Escherichia coli, and the GFPuv mutant containing D-phenylalanine in the fluorophore at residue 66 was characterized. Stereochemical switching of phenylalanine at position 66 resulted in red shifts in the emission and excitation maxima and significantly improved the thermal stability of the protein. Molecular modeling further revealed that the opposite configurations of Phe66 in GFPuv produced two respective isomeric fluorophores that exhibit distinctive spectral properties and thermal stability. The present study expands the backbone stereochemistry of protein molecules by in vivo ribosomal translation to facilitate protein engineering.

Substrate inhibition is a universal challenge in biocatalytic process development. Herein, a controlled release of substrate from the microparticles was introduced and demonstrated to tackle this issue to increase the biocatalytic efficiency. Using phenylalanine dehydrogenase catalyzed production of l-homophenylalanine as a model reaction, and substrate-loaded microparticles were prepared and used as a reservoir to load a high amount of substrate and to control the release rate into the reaction media. Consequently, highly efficient biocatalysis could be sustainably achieved in the complex reaction system through constantly lowering the substrate concentration.Keywords: biocatalysis; controlled release; l-homophenylalanine; microparticle; substrate inhibition

The regulatory elements for nosiheptide biosynthesis were identified by a novel host–vector system with an endogenous gene within the biosynthetic gene cluster as a reporter gene. The present study offers a rapid and reliable method for the identification of regulatory elements in the biosynthesis of various bioactive natural products.

A novel thiol fluorophore was synthesized to be selectively attached to the non-reducing end of low molecular weight heparin (LMWH) via a Michael addition. Double labeling of LMWH was demonstrated to be a feasible approach for the determination of heparinase II activity by FRET.

l-Norephedrine, a natural plant alkaloid, possesses similar activity as ephedrine and can be used as a vicinal amino alcohol for the asymmetric synthesis of a variety of optically pure compounds, including pharmaceuticals, fine chemicals, and agrochemicals. Because of the existence of two asymmetric centers, efficient synthesis of l-norephedrine has been challenging. In the present study, an R-selective pyruvate decarboxylase from Saccharomyces cerevisiae and an S-selective ω-transaminase from Vibrio fluvialis JS17 were coupled to develop a sequential process for the stereoselective biosynthesis of l-norephedrine. After systematic optimization of the reaction conditions, a green, economic, and practical biocatalytic method to prepare l-norephedrine was established to achieve de and ee values of greater than 99.5 % and a molar yield over 60 %. The present coupling approach can facilitate the development of sequential reactions by various biocatalysts.

Enantiomerically pure l-homophenylalanine (l-HPA) is a key building block for the synthesis of angiotensin-converting enzyme inhibitors and other chiral pharmaceuticals. Among the processes developed for the l-HPA production, biocatalytic synthesis employing phenylalanine dehydrogenase has been proven as the most promising route. However, similar to other dehydrogenase-catalyzed reactions, the viability of this process is markedly affected by insufficient substrate loading and high costs of the indispensable cofactors. In the present work, a highly efficient and economic biocatalytic process for l-HPA was established by coupling genetically modified phenylalanine dehydrogenase and formate dehydrogenase. Combination of fed-batch substrate addition and a continuous product removal greatly increased substrate loading and cofactor utilization. After systemic optimization, 40 g (0.22 mol) of keto acid substrate was transformed to l-HPA within 24 h and a total of 0.2 mM NAD+ was reused effectively in eight cycles of fed-batch operation, consequently giving an average substrate concentration of 510 mM and a productivity of 84.1 g l−1 day−1 for l-HPA. The present study provides an efficient and feasible enzymatic process for the production of l-HPA and a general solution for the increase of substrate loading.

Chiral diols are a group of key building blocks useful for preparing a variety of important chiral chemicals. While the preparation of optically pure diols is generally not an easy task in synthetic organic chemistry, three classes of enzymes, namely dicarbonyl reductase, dioxygenase and epoxide hydrolase, display remarkable ability to stereoselectively introduce two hydroxyl groups in a single-step enzymatic conversion. In this tutorial review, we pay special attention to dicarbonyl reductases that directly produce chiral diols through the bio-reduction of two carbonyl groups. The dicarbonyl reductases include diketoreductase, α-acetoxy ketone reductase and sepiapterin reductase. We present these exceptional enzymes in the context of source and properties, structure and catalytic mechanism as well as biocatalytic application. In addition to the broad substrate specificity, the excellent stereoselectivity and high catalytic efficiency of these enzymes have positioned them as valuable biocatalysts. With more sophisticated understanding of the structure–function relationship, the practical utilities of these enzymes associated with their interesting chemistry will be considerably appreciated over time. Moreover, rational redesign and molecular evolution of these unusual biocatalysts will truly enable their broader applications in the synthesis of chiral diols in the future.

Diketoreductase catalyzes a two-step bioreduction on a dicarbonyl substrate through a novel dual catalysis mode, in which random hydride attack simultaneously forms two mono-carbonyl intermediates, and subsequently distinct catalytic sites are responsible for the reductions of respective carbonyl group of the intermediates to yield the final dihydroxy product.

Dynamic change of intracellular nicotinamide cofactor concentrations, the limiting factor for the bioreductions catalyzed by oxidoreductases, was monitored in Escherichia coli cells coexpressing diketoreductase and glucose dehydrogenase. On the basis of an unexpected observation, a relationship between catalytic efficiency and cofactor concentrations was established to optimize the process for the preparation of a chiral diol for statin drugs. Consequently, compared to previous reactions by E. coli cells expressing diketoreductase alone, exogenous addition of cofactors was completely eliminated to yield an increase of substrate concentration by 15-fold. The present strategy could be employed in the biocatalytic processes catalyzed by nicotinamide-dependent oxidoreductases.Keywords: coexpression; diketoreductase; glucose dehydrogenase; nicotinamide cofactor; statin drugs; whole-cell biocatalysis;

Polymerase chain reaction (PCR) is a basic technique with wide applications in molecular biology. Despite the development of different methods with various modifications, the amplification of GC-rich DNA fragments is frequently troublesome due to the formation of complex secondary structure and poor denaturation. Given the fact that GC-rich genes are closely related to transcriptional regulation, transcriptional silencing, and disease progression, we developed a PCR method combining a stepwise procedure and a mixture of additives in the present work. Our study demonstrated that the PCR method could successfully amplify targeted DNA fragments up to 1.2 Kb with GC content as high as 83.5% from different species. Compared to all currently available methods, our work showed satisfactory, adaptable, fast and efficient (SAFE) results on the amplification of GC-rich targets, which provides a versatile and valuable tool for the diagnosis of genetic disorders and for the study of functions and regulations of various genes.

The complete separation of structurally similar compounds has been a challenge due mainly to their similarity on physical and chemical properties. In the present study, a simple and effective chromatographic method to separate and purify nocathiacin acid from its structural analogue nocathiacin I was developed. After evaluating mobile phase compositions on the retention characteristics by reversed phase high-performance liquid chromatography (HPLC), the elution order of nocathiacin I and nocathiacin acid was completely reversed, and the resolution value between the two analogues was improved, by varying pH value and ionic strength, to greater than 10 from merged peaks under initial conditions. In addition, a preparative isolation of nocathiacin acid was performed by reversed phase column chromatography under the guidance of the HPLC study. This chromatographic method resulted in an efficient process to obtain pure nocathiacin acid with a recovery rate of 83%. The present approach offers a new methodology for the separation of structurally closely related secondary metabolites.

Recombinant diketoreductase showed excellent stereoselectivity in the double reduction of β,δ-diketo esters. To investigate the substrate specificity and to broaden the applications of this new biocatalyst, a number of ketone substrates were used to evaluate the substrate spectrum and enantioselectivity of this enzyme in the present study. Among the ketone substrates tested, only this enzyme displayed high efficiency and excellent enantioselectivity in the reduction of ethyl 2-oxo-4-phenylbutyrate to ethyl (S)-2-hydroxy-4-phenylbutyrate. After optimizing the reaction conditions, the bio-reduction of ethyl 2-oxo-4-phenylbutyrate at a substrate concentration of 0.8 M (164.8 g/L) was achieved by the recombinant diketoreductase in an aqueous-toluene biphasic system coupled with formate dehydrogenase for the regeneration of cofactor, resulting in an overall hydroxyl product yield of 88.7% (99.5% ee). This new enzymatic transformation may offer a practical method for the preparation of this important chiral building block.

Diketoreductase catalyzes a two-step bioreduction on a dicarbonyl substrate through a novel dual catalysis mode, in which random hydride attack simultaneously forms two mono-carbonyl intermediates, and subsequently distinct catalytic sites are responsible for the reductions of respective carbonyl group of the intermediates to yield the final dihydroxy product.

Chiral diols are a group of key building blocks useful for preparing a variety of important chiral chemicals. While the preparation of optically pure diols is generally not an easy task in synthetic organic chemistry, three classes of enzymes, namely dicarbonyl reductase, dioxygenase and epoxide hydrolase, display remarkable ability to stereoselectively introduce two hydroxyl groups in a single-step enzymatic conversion. In this tutorial review, we pay special attention to dicarbonyl reductases that directly produce chiral diols through the bio-reduction of two carbonyl groups. The dicarbonyl reductases include diketoreductase, α-acetoxy ketone reductase and sepiapterin reductase. We present these exceptional enzymes in the context of source and properties, structure and catalytic mechanism as well as biocatalytic application. In addition to the broad substrate specificity, the excellent stereoselectivity and high catalytic efficiency of these enzymes have positioned them as valuable biocatalysts. With more sophisticated understanding of the structure–function relationship, the practical utilities of these enzymes associated with their interesting chemistry will be considerably appreciated over time. Moreover, rational redesign and molecular evolution of these unusual biocatalysts will truly enable their broader applications in the synthesis of chiral diols in the future.

A novel thiol fluorophore was synthesized to be selectively attached to the non-reducing end of low molecular weight heparin (LMWH) via a Michael addition. Double labeling of LMWH was demonstrated to be a feasible approach for the determination of heparinase II activity by FRET.

The regulatory elements for nosiheptide biosynthesis were identified by a novel host–vector system with an endogenous gene within the biosynthetic gene cluster as a reporter gene. The present study offers a rapid and reliable method for the identification of regulatory elements in the biosynthesis of various bioactive natural products.