Sequence- and structure-guided improvement of the catalytic performance of a GH11 family xylanase from Bacillus subtilis

Improving the inhibitory resistance of xylanase FgXyn11C from Fusarium graminearum to SyXIP-I by site-directed mutagenesis

The aim of this study was to improve the inhibitory resistance of xylanase FgXyn11C from Fusarium graminearum to XIP in cereal flour. Site saturation mutagenesis was performed using computer-aided redesign. Firstly, based on multiple primary structure alignments, the amino acid residues in the active site architecture were identified, and specific residue T144 in the thumb region of FgXyn11C was selected for site-saturation mutagenesis. After screening, FgXyn11CT144F was selected as the best mutant, as it displayed the highest enzymatic activity and resistance simultaneously compared to other mutants. The specific activity of FgXyn11CT144F was 208.8 U/mg and it exhibited complete resistance to SyXIP-I. Compared with the wild-type, FgXyn11CT144F displayed similar activity and the most resistant against SyXIP-I. The optimal temperature and pH of the wild-type and purified FgXyn11CT144F were similar at pH 5.0 and 30 °C. Our findings provided preliminary insight into how the specific residue at position 144 in the thumb region of FgXyn11C influenced the enzymatic properties and interacted with SyXIP-I. The inhibition sensitivity of FgXyn11C was reduced through directed evolution, leading to creation of the mutant enzyme FgXyn11CT144F. The FgXyn11CT144F resistance to SyXIP-I has potential application and can also provide references for engineering other resistant xylanases of the GHF11.

Improvement of thermostability and catalytic efficiency of xylanase from Myceliophthora thermophilar by N-terminal and C-terminal truncation

Introduction

Extracting xylanase from thermophilic filamentous fungi is a feasible way to obtain xylanase with good thermal stability.

Methods

The transcriptomic data of Myceliophthora thermophilic destructive ATCC42464 were differentially expressed and enriched. By comparing the sequences of Mtxylan2 and more than 10 xylanases, the N-terminal and C-terminal of Mtxylan2 were truncated, and three mutants 28N, 28C and 28NC were constructed.

Results and discussion

GH11 xylan Mtxylan2 was identified by transcriptomic analysis, the specific enzyme activity of Mtxylan2 was 104.67 U/mg, and the optimal temperature was 65°C. Molecular modification of Mtxylan2 showed that the catalytic activity of the mutants was enhanced. Among them, the catalytic activity of 28C was increased by 9.3 times, the optimal temperature was increased by 5°C, and the residual enzyme activity remained above 80% after 30 min at 50-65°C, indicating that redundant C-terminal truncation can improve the thermal stability and catalytic performance of GH11 xylanase.

Rational Design of l-Threonine Transaldolase-Mediated System for Enhanced Florfenicol Intermediate Production

l-threo-p-methylsulfonylphenylserine (compound 1b) is the main intermediate of florfenicol, and its efficient synthesis has been the subject of current research. Herein, Burkholderia diffusa l-threonine transaldolase (BuLTTA) was rationally designed based on the sequence-structure-function relationship. A mutant M4 (Asn35Ser/Thr352Asn) could produce 35.5 mM 1b with 88.8% conversion and 93.8% diastereoselectivity, 314 and 129% of the values observed for wild-type BuLTTA. Molecular dynamics simulations indicated that the shortened distance between key active site residues and the transition state (PLP-1b) and the improved hydrogen bond force enhanced the catalytic performance of the M4 variant. Then, the mutant M4 was combined with K. kurtzmanii alcohol dehydrogenase (KkADH) to eliminate the BuLTTA-inhibiting byproduct acetaldehyde, and a cosubstrate was added to regenerate the ADH cofactor NADH. Under optimized conditions, the yield of 1b reached 115.2 mM with a conversion of 96% and a diastereoselectivity of 95.5%. This work provides a new strategy for the efficient and sustainable production of 1b.

Structure-guided engineering of branched-chain α-keto acid decarboxylase for improved 1,2,4-butanetriol production by in vitro synthetic enzymatic biosystem

Efficient synthetic routes for biomanufacturing chemicals often require the overcoming of pathway bottlenecks by tailoring enzymes to improve the catalytic efficiency or even implement non-native activities. 1,2,4-butanetriol (BTO), a valuable commodity chemical, is currently biosynthesized from D-xylose via a four-enzyme reaction cascade, with the ThDP-dependent α-keto acid decarboxylase (KdcA) identified as the potential bottleneck. Here, to further enhance the catalytic activity of KdcA toward the non-native substrate α-keto-3-deoxy-xylonate (KDX), in silico screening and structure-guided evolution were performed. The best mutants, S286L/G402P and V461K, exhibited a 1.8- and 2.5-fold higher enzymatic activity in the conversion of KDX to 3,4-dihydroxybutanal when compared to KdcA, respectively. MD simulations revealed that the two sets of mutations reshaped the substrate binding pocket, thereby increasing the binding affinity for KDX and promoting interactions between KDX and cofactor ThDP. Then, when the V461K mutant instead of wild type KdcA was integrated into the enzyme cascade, a 1.9-fold increase in BTO titer was observed. After optimization of the reaction conditions, the enzyme cocktail contained V461K converted 60 g/L D-xylose to 22.1 g/L BTO with a yield of 52.1 %. This work illustrated that protein engineering is a powerful tool for modifying the output of metabolic pathway.

Simultaneously Enhanced Thermostability and Catalytic Activity of Xylanase from Streptomyces rameus L2001 by Rigidifying Flexible Regions in Loop Regions of the N-Terminus

The GH11 xylanase XynA from Streptomyces rameus L2001 has favorable hydrolytic properties. However, its poor thermal stability hinders its widespread application in industry. In this study, mutants Mut1 and Mut2 were constructed by rationally combining the mutations 11YHDGYF16, 23AP24/23SP24, and 32GP33. The residual enzyme activity of these combinational mutants was more than 85% when incubated at 80 and 90 °C for 12 h, and thus are the most thermotolerant xylanases known to date. The reduced flexibility of the N-terminus, increased overall rigidity, as well as the surface net charge of Mut1 and Mut2 may be partially responsible for the improved thermal stability. In addition, the specific activity and catalytic efficiency of Mut1 and Mut2 were improved compared with those of wild-type XynA. The broader catalytic cleft and enhanced flexibility of the "thumb" of Mut1 and Mut2 may be partially responsible for the improved specific activity and catalytic efficiency.

Enabling technology and core theory of synthetic biology

Synthetic biology provides a new paradigm for life science research ("build to learn") and opens the future journey of biotechnology ("build to use"). Here, we discuss advances of various principles and technologies in the mainstream of the enabling technology of synthetic biology, including synthesis and assembly of a genome, DNA storage, gene editing, molecular evolution and de novo design of function proteins, cell and gene circuit engineering, cell-free synthetic biology, artificial intelligence (AI)-aided synthetic biology, as well as biofoundries. We also introduce the concept of quantitative synthetic biology, which is guiding synthetic biology towards increased accuracy and predictability or the real rational design. We conclude that synthetic biology will establish its disciplinary system with the iterative development of enabling technologies and the maturity of the core theory.

Three Molecular Modification Strategies to Improve the Thermostability of Xylanase XynA from Streptomyces rameus L2001

Glycoside hydrolase family 11 (GH11) xylanases are the preferred candidates for the production of functional oligosaccharides. However, the low thermostability of natural GH11 xylanases limits their industrial applications. In this study, we investigated the following three strategies to modify the thermostability of xylanase XynA from Streptomyces rameus L2001 mutation to reduce surface entropy, intramolecular disulfide bond construction, and molecular cyclization. Changes in the thermostability of XynA mutants were analyzed using molecular simulations. All mutants showed improved thermostability and catalytic efficiency compared with XynA, except for molecular cyclization. The residual activities of high-entropy amino acid-replacement mutants Q24A and K104A increased from 18.70% to more than 41.23% when kept at 65 °C for 30 min. The catalytic efficiencies of Q24A and K143A increased to 129.99 and 92.26 mL/s/mg, respectively, compared with XynA (62.97 mL/s/mg) when using beechwood xylan as the substrate. The mutant enzyme with disulfide bonds formed between Val3 and Thr30 increased the t_1/2^{60 °C} by 13.33-fold and the catalytic efficiency by 1.80-fold compared with the wild-type XynA. The high thermostabilities and hydrolytic activities of XynA mutants will be useful for enzymatic production of functional xylo-oligosaccharides.

Recent advancements in prebiotic oligomers synthesis via enzymatic hydrolysis of lignocellulosic biomass

Interest in functional food, such as non-digestible prebiotic oligosaccharides is increasing day by day and their production is shifting toward sustainable manufacturing. Due to the presence of high carbohydrate content, lignocellulosic biomass (LCB) is the most-potential, cost-effective and sustainable substrate for production of many useful products, including lignocellulose-derived prebiotic oligosaccharides (LDOs). These have the same worthwhile properties as other common oligosaccharides, such as short chain carbohydrates digestible to the gut flora but not to humans mainly due to their resistance to the low pH and high temperature and their demand is constantly increasing mainly due to increased awareness about their potential health benefits. Despite several advantages over the thermo-chemical route of synthesis, comprehensive and updated information on the conversion of lignocellulosic biomass to prebiotic oligomers via controlled enzymatic saccharification is not available in the literature. Thus, the main objective of this review is to highlight recent advancements in enzymatic synthesis of LDOs, current challenges, and future prospects of sustainably producing prebiotic oligomers via enzymatic hydrolysis of LCB substrates. Enzyme reaction engineering practices, custom-made enzyme preparations, controlled enzymatic hydrolysis, and protein engineering approaches have been discussed with regard to their applications in sustainable synthesis of lignocellulose-derived oligosaccharide prebiotics. An overview of scale-up aspects and market potential of LDOs has also been provided.