Enzymatic dynamic kinetic resolution of racemic N-formyl- and N-carbamoyl-amino acids using immobilized l-N-carbamoylase and N-succinyl-amino acid racemase

Nanostructured supports for multienzyme co-immobilization for biotechnological applications: Achievements, challenges and prospects

The synergistic combination of current biotechnological and nanotechnological research has turned to multienzyme co-immobilization as a promising concept to design biocatalysis engineering. It has also intensified the development and deployment of multipurpose biocatalysts, for instance, multienzyme co-immobilized constructs, via biocatalysis/protein engineering to scale-up and fulfil the ever-increasing industrial demands. Considering the characteristic features of both the loaded multienzymes and nanostructure carriers, i.e., selectivity, specificity, stability, resistivity, induce activity, reaction efficacy, multi-usability, high catalytic turnover, optimal yield, ease in recovery, and cost-effectiveness, multienzyme-based green biocatalysts have become a powerful norm in biocatalysis/protein engineering sectors. In this context, the current state-of-the-art in enzyme engineering with a synergistic combination of nanotechnology, at large, and nanomaterials, in particular, are significantly contributing and providing robust tools to engineer and/or tailor enzymes to fulfil the growing catalytic and contemporary industrial needs. Considering the above critics and unique structural, physicochemical, and functional attributes, herein, we spotlight important aspects spanning across prospective nano-carriers for multienzyme co-immobilization. Further, this work comprehensively discuss the current advances in deploying multienzyme-based cascade reactions in numerous sectors, including environmental remediation and protection, drug delivery systems (DDS), biofuel cells development and energy production, bio-electroanalytical devices (biosensors), therapeutical, nutraceutical, cosmeceutical, and pharmaceutical oriented applications. In conclusion, the continuous developments in nano-assembling the multienzyme loaded co-immobilized nanostructure carriers would be a unique way that could act as a core of modern biotechnological research.

Measurement of Minute Liquid Volumes of Chiral Molecules Using In-Fiber Polarimetry

We report an optofluidic method that enables to efficiently measure the enantiomeric excess of chiral molecules at low concentrations. The approach is to monitor the optical activity induced by a Kagome-lattice hollow-core photonic crystal fiber filled with a sub-μL volume of chiral compounds. The technique also allows monitoring the enzymatic racemization of R-mandelic acid.

The N-Acetyl Amino Acid Racemases (NAAARs); Native and evolved biocatalysts applied to the synthesis of canonical and non-canonical amino acids

Amino acids are one of the most important synthons employed in the biotechnology, pharmaceutical and agrochemical industries for the preparation of active agents. Recently, the emerging use of these compounds as tools for protein engineering, has also been reported. Numerous chemo- and biocatalytic strategies have been developed for the stereoselective synthesis of these compounds. One of the most efficient processes is the enzymatic dynamic kinetic resolution of N-acylated derivatives, where an N-acyl amino acid racemase (NAAAR) is coupled with an enantioselective, hydrolytic enzyme (aminoacylase), and used to convert a racemic mixture of starting materials to enantiopure products. Here we provide a brief overview of the structure and mechanism of NAAAR. We will also review the applications of this class of biocatalyst, as well as discussing the various strategies employed to obtain an efficient system for the synthesis of optically pure canonical and non-canonical amino acids.

Immobilization of an amino acid racemase for application in crystallization-based chiral resolutions of asparagine monohydrate

Integration of racemization and a resolution process is an attractive way to overcome yield limitations in the production of pure chiral molecules. Preferential crystallization and other crystallization-based techniques usually produce low enantiomeric excess in solution, which is a constraint for coupling with racemization. We developed an enzymatic fixed bed reactor that can potentially overcome these unfavorable conditions and improve the overall yield of preferential crystallization. Enzyme immobilization strategies were investigated on covalent-binding supports. The amino acid racemase immobilized in Purolite ECR 8309F with a load of 35 mg-enzyme/g-support showed highest specific activity (approx. 500 U/g-support) and no loss in activity in reusability tests. Effects of substrate inhibition observed for the free enzyme were overcome after immobilization. A packed bed reactor with the immobilized racemase showed good performance in steady state operation processing low enantiomeric excess inlet. Kinetic parameters from batch reactor experiments can be successfully used for prediction of packed bed reactor performance. Full conversions could be achieved for residence times above 1.1 min. The results suggest the potential of the prepared racemase reactor to be combined with preferential crystallization to improve resolution of asparagine enantiomers.

Overview on Multienzymatic Cascades for the Production of Non-canonical α-Amino Acids

The 22 genetically encoded amino acids (AAs) present in proteins (the 20 standard AAs together with selenocysteine and pyrrolysine), are commonly referred as proteinogenic AAs in the literature due to their appearance in ribosome-synthetized polypeptides. Beyond the borders of this key set of compounds, the rest of AAs are generally named imprecisely as non-proteinogenic AAs, even when they can also appear in polypeptide chains as a result of post-transductional machinery. Besides their importance as metabolites in life, many of D-α- and L-α-"non-canonical" amino acids (NcAAs) are of interest in the biotechnological and biomedical fields. They have found numerous applications in the discovery of new medicines and antibiotics, drug synthesis, cosmetic, and nutritional compounds, or in the improvement of protein and peptide pharmaceuticals. In addition to the numerous studies dealing with the asymmetric synthesis of NcAAs, many different enzymatic pathways have been reported in the literature allowing for the biosynthesis of NcAAs. Due to the huge heterogeneity of this group of molecules, this review is devoted to provide an overview on different established multienzymatic cascades for the production of non-canonical D-α- and L-α-AAs, supplying neophyte and experienced professionals in this field with different illustrative examples in the literature. Whereas the discovery of new or newly designed enzymes is of great interest, dusting off previous enzymatic methodologies by a "back and to the future" strategy might accelerate the implementation of new or improved multienzymatic cascades.

Evaluation of Designed Immobilized Catalytic Systems: Activity Enhancement of Lipase B from Candida antarctica

Immobilized enzymatic catalysts are widely used in the chemical and pharmaceutical industries. As Candida antarctica lipase B (CALB) is one of the more commonly used biocatalysts, we attempted to design an optimal lipase-catalytic system. In order to do that, we investigated the enantioselectivity and lipolytic activity of CALB immobilized on 12 different supports. Immobilization of lipase on IB-D152 allowed us to achieve hyperactivation (178%) in lipolytic activity tests. Moreover, the conversion in enantioselective esterification increased 43-fold, when proceeding with lipase-immobilized on IB-S861. The immobilized form exhibited a constant high catalytic activity in the temperature range of 25 to 55 °C. Additionally, the lipase immobilized on IB-D152 exhibited a higher lipolytic activity in the pH range of 6 to 9 compared with the native form. Interestingly, our investigations showed that IB-S500 and IB-S60S offered a possibility of application in catalysis in both organic and aqueous solvents. A significant link between the reaction media, the substrates, the supports and the lipase was confirmed. In our enzymatic investigations, high-performance liquid chromatography (HPLC) and the titrimetric method, as well as the Bradford method were employed.

N-succinylamino acid racemases: Enzymatic properties and biotechnological applications

The N-succinylamino acid racemase/o-succinylbenzoate synthase (NSAR/OSBS) subfamily from the enolase superfamily contains different enzymes showing promiscuous N-substituted-amino acid racemase (NxAR) activity. These enzymes were originally named as N-acylamino acid racemases because of their industrial application. Nonetheless, they are pivotal in several enzymatic cascades due to their versatility to catalyze a wide substrate spectrum, allowing the production of optically pure d- or l-amino acids from cheap precursors. These compounds are of paramount economic interest, since they are used as food additives, in the pharmaceutical and cosmetics industries and/or as chiral synthons in organic synthesis. Despite its economic importance, the discovery of new N-succinylamino acid racemases has become elusive, since classical sequence-based annotation methods proved ineffective in their identification, due to a high sequence similarity among the members of the enolase superfamily. During the last decade, deeper investigations into different members of the NSAR/OSBS subfamily have shed light on the classification and identification of NSAR enzymes with NxAR activity of biotechnological potential. This review aims to gather the dispersed information on NSAR/OSBS members showing NxAR activity over recent decades, focusing on their biotechnological applications and providing practical advice to identify new enzymes.

Toward a cell-free hydantoinase process: screening for expression optimization and one-step purification as well as immobilization of hydantoinase and carbamoylase

The hydantoinase process is applied for the industrial synthesis of optically pure amino acids via whole cell biocatalysis, providing a simple and well-established method to obtain the catalyst. Nevertheless, whole cell approaches also bear disadvantages like intracellular degradation reactions, transport limitations as well as low substrate solubility. In this work the hydantoinase and carbamoylase from Arthrobacter crystallopoietes DSM 20117 were investigated with respect to their applicability in a cell-free hydantoinase process. Both enzymes were heterologously expressed in Escherichia coli BL21DE3. Cultivation and induction of the hydantoinase under oxygen deficiency resulted in markedly higher specific activities and a further increase in expression was achieved by codon-optimization. Further expression conditions of the hydantoinase were tested using the microbioreactor system BioLector^®, which showed a positive effect upon the addition of 3% ethanol to the cultivation medium. Additionally, the hydantoinase and carbamoylase were successfully purified by immobilized metal ion affinity using Ni Sepharose beads as well as by functionalized magnetic beads, while the latter method was clearly more effective with respect to recovery and purification factor. Immobilization of both enzymes via functionalized magnetic beads directly from the crude cell extract was successful and resulted in specific activities that turned out to be much higher than those of the purified free enzymes.