Site-directed mutation to improve the enzymatic activity of 5-carboxy-2-pentenoyl-CoA reductase for enhancing adipic acid biosynthesis

Unveiling the power of MXenes: Solid lubrication perspectives and future directions

The interaction between two surfaces leads to the generation of friction and wear of material. Friction and wear are some of the major challenges that may readily be overcome by the third part of tribology called lubrication. Utilizing solid lubricants including polymers, carbon-based materials, soft metals, transition metal dichalcogenides, along with their potential benefits and drawbacks in dry environments can reduce friction. Recently, an emerging class of two-dimensional (2D) transition metal nitrides, carbides or carbonitrides commonly known as MXenes have emerged as an attractive alternative for solid lubrication because of their ability to establish wear-resistant tribo layers and well as low friction and shear strength. Furthermore, the inherent hydrophilic nature of these substances has led to limited dispersion stability and phase compatibility when combined with pure base oils. As a result, their potential use as solid lubricants and lubricant additives has been impeded. To address this issue and enhance the applicability of MXenes as solid lubricants, their surface modification can be an attractive tool. Therefore, this review provides a succinct summary of the current state-of-the-art in surface functionalization of MXenes, a subject that has not yet been thoroughly addressed. Further, the mechanical behavior of MXenes and composites has been discussed, followed by the potential of MXenes as a solid lubricant at micro- and macro-scale. Finally, the existing opportunities and challenges of the research area have been discussed with possible future research directions. We believe, this article will be a valuable resource for MXenes and opens the door to improve the chemical, physical and mechanical properties of MXenes in various applications, such as solid lubrication.

Characterization of aspartokinase double mutants using a combination of experiments and simulations

Aspartokinase (AK) is synergistically suppressed by Thr and Lys in the Corynebacterium metabolic pathway. Site-directed mutations can significantly improve AK inhibition. Our previous studies confirmed that sites 379 and 380 were important sites affecting enzyme activity, so we further screen the double mutants with excellent enzymatic properties from sites 379 and 380, and discuss the difference of enzyme activity between the double mutants and single mutants. Here, a double mutant, T379L/A380 M, with improved enzyme activity (2.74-fold) was obtained. Enzymatic property experiments showed that the optimum temperature of T379L/A380 M increased from 26 °C (recombinant Escherichia coli; WT-AK) to 45 °C and that the optimal pH decreased from 8.0 (WT-AK) to 7.5. Further, the half-life decreased from 4.5 to 3.32 h. These enzymatic properties were better than other mutant strains. Inhibition was diminished with low concentrations of Lys, and Lys + Thr presented an activating role. Subsequently, the reasons for the improved AK enzyme activity were illustrated with microscale thermophoresis (MST) experiments and molecular dynamic (MD) simulation by measuring ligand affinity and AK conformational changes. MST showed that the affinity between T379L/A380 M and Lys decreased, but the affinity between T379L/A380 M and Asp increased, promoting T379L/A380 M enzyme activity. MD experiments showed that T379L/A380 M enhanced the Asp-ATP affinity and catalyzed the transfer of residues S192 and D193 to Asp, promoting T379L/A380 M enzyme activity. However, the mutation did not cause fluctuations in the substrate Asp and ATP pockets. This might be why the enzyme activity was inferior to that of the single mutants (T379L and A380 M).

Recent advances in microbial production of diamines, aminocarboxylic acids, and diacids as potential platform chemicals and bio-based polyamides monomers

Recently, bio-based manufacturing processes of value-added platform chemicals and polymers in biorefineries using renewable resources have extensively been developed for sustainable and carbon dioxide (CO₂) neutral-based industry. Among them, bio-based diamines, aminocarboxylic acids, and diacids have been used as monomers for the synthesis of polyamides having different carbon numbers and ubiquitous and versatile industrial polymers and also as precursors for further chemical and biological processes to afford valuable chemicals. Until now, these platform bio-chemicals have successfully been produced by biorefinery processes employing enzymes and/or microbial host strains as main catalysts. In this review, we discuss recent advances in bio-based production of diamines, aminocarboxylic acids, and diacids, which has been developed and improved by systems metabolic engineering strategies of microbial consortia and optimization of microbial conversion processes including whole cell bioconversion and direct fermentative production.

Claisen condensation reaction mediated pimelate biosynthesis via the reverse adipate-degradation pathway and its isoenzymes

Pimelic acid is an important seven-carbon dicarboxylic acid, which is broadly applied in various fields. The industrial production of pimelic acid is mainly through chemical method, which is complicated and environment unfriendly. Herein, we found that pimelic acid could be biosynthesized by the reverse adipate-degradation pathway (RADP), a typical Claisen condensation reaction that could be applied to the arrangement of C-C bond. In order to strengthen the supply of glutaryl-CoA precursor, PA5530 protein was used to transport glutaric acid. Subsequently, we discovered that the enzymes in the BIOZ pathway was isoenzymes with the RADP. By combining the isoenzymes of the two pathways, the titer of pimelic acid reached 36.7 mg·L -1 under the optimal combination, which was increased by 382.9% compared with the control strain B-3. It was also the highest titer of pimelic acid biosynthesized by Claisen condensation reaction, laying foundations for further pimelic acid and its derivatives production.

Research status of Bacillus phytase

Phytic acid is abundant in seeds, roots and stems of plants, it acts as an anti-nutrient in food and feed industry, since it affects the absorption of nutrients by humans and monogastric animals. Furthermore, phosphorus produced through its decomposition by microorganisms can cause environmental pollution. Phytase degrades phytic acid generating precursors of inositol that can be used in clinical practice; in addition, phytase treatment can minimize the anti-nutritional effect of phytic acid. The use of phytase synthesized from Bacillus is more advantageous due to its high activity. Additionally, its good heat resistance under neutral conditions greatly fills the gap of commercial utilization of acid phytase. In this review, we summarize the latest research results on Bacillus phytase, including its physiological and biochemical characteristics, molecular structure information, calcium effects on its catalytic activity and stability, its catalytic mechanism and molecular modification.

Characterization of a short-chain dehydrogenase/reductase and its function in patulin biodegradation in apple juice

Biodegradation based on microbial enzymes is considered to be one of the promising ways for controlling patulin contamination. However, few patulin degrading enzymes have been isolated and characterized until now. Here, a short-chain dehydrogenase/reductase (SDR) gene, CgSDR, was cloned from a yeast strain Candida guilliermondii, and expressed in Escherichia coli. The expression of CgSDR conferred a strong patulin tolerance and degradation ability to E. coli, and purified CgSDR could transform patulin into E-ascladiol in vitro with NADPH as a coenzyme. Moreover, addition of CgSDR at 150 μg/mL could reduce 80% of patulin in apple juice and the biodegradation process did not affect the quality of the apple juice. A molecular docking analysis and site-directed mutagenesis indicated that CgSDR might interact with patulin via VAL188 as an active binding sites. The findings provide new insights for developing enzymic formulations for mycotoxin detoxification in fruit derived products.

Recent Progress in Adipic Acid Synthesis Over Heterogeneous Catalysts

Adipic acid is one of the most important feedstocks for producing resins, nylons, lubricants, plasticizers. Current industrial petrochemical process, producing adipic acid from KA oil, catalyzed by nitric acid, has a serious pollution to the environment, due to the formation of waste nitrous oxide. Hence, developing cleaner methods to produce adipic acid has attracted much attention of both industry and academia. This mini-review article discussed advances on adipic acid synthesis from bio-renewable feedstocks, as well as most recent progress on cleaner technology from fossil fuels over novel catalytic materials. This work on recent advances in green adipic acid production will provide insights and guidance to further study of various other industrial processes for producing nylon precursors.