Engineering the thermostability of d-lyxose isomerase from Caldanaerobius polysaccharolyticus via multiple computer-aided rational design for efficient synthesis of d-mannose

Characterization of Runella zeae D-mannose 2-epimerase and its expression in Bacillus subtilis for D-mannose production from D-glucose

D-Mannose 2-epimerase (MEase) catalyzes the bioconversion between D-glucose and D-mannose. It is an important potential biocatalyst for large-scale production of D-mannose, a functional monosaccharide used in pharmaceutical and food industries. In this study, a new microbial MEase was characterized from Runella zeae DSM 19591. The enzyme was purified by one-step nickel-affinity chromatography and determined to be a dimeric protein with two identical subunits of approximately 86.1 kDa by gel filtration. The enzyme showed the highest activity at pH 8.0 and 40 °C, with a specific activity of 2.99 U/mg on D-glucose and 3.71 U/mg on D-mannose. The melting temperature (Tm) was 49.4 °C and the half-life was 115.14 and 3.23 h at 35 and 40 °C, respectively. The purified enzyme (1 U/mL) produced 115.7 g/L of D-mannose from 500 g/L of D-glucose for 48 h, with a conversion ratio of 23.14 %. It was successfully expressed in Bacillus subtilis WB600 via pP43NMK as the vector. The highest fermentation activity was 10.58 U/mL after fed-batch cultivation for 28 h, and the whole cells of recombinant B. subtilis produced 114.0 g/L of D-mannose from 500 g/L of D-glucose, with a conversion ratio of 22.8 %.

Advancing sustainable biotechnology through protein engineering

The push for industrial sustainability benefits from the use of enzymes as a replacement for traditional chemistry. Biological catalysts, especially those that have been engineered for increased activity, stability, or novel function, and are often greener than alternative chemical approaches. This Review highlights the role of engineered enzymes (and identifies directions for further engineering efforts) in the application areas of greenhouse gas sequestration, fuel production, bioremediation, and degradation of plastic wastes.

Improving the catalytic activity and thermostability of Aspergillus niger xylanase through computational design

Xylanase plays the most important role in catalyzing xylan to xylose moieties. GH11 xylanases have been widely used in many fields, but most GH11 xylanases are mesophilic enzymes. To improve the catalytic activity and thermostability of Aspergillus niger xylanase (Xyn-WT), we predicted potential key mutation sites of Xyn-WT through multiple computer-aided enzyme engineering strategies. We introduce a simple and economical Ni affinity chromatography purification method to obtain high-purity xylanase and its mutants. Ten mutants (Xyn-A, Xyn-B, Xyn-C, E45T, Q93R, E45T/Q93R, A161P, Xyn-D, Xyn-E, Xyn-F) were identified. Among the ten mutants, four (Xyn-A, Xyn-C, A161P, Xyn-F) presented improved thermal stability and activity, with Xyn-F(A161P/E45T/Q93R) being the most thermally stable and active. Compared with Xyn-WT, after heat treatment at 55 °C and 60 °C for 10 min, the remaining enzyme activity of Xyn-F was 12 and 6 times greater than that of Xyn-WT, respectively, and Xyn-F was approximately 1.5 times greater than Xyn-WT when not heat treated. The pH adaptation of Xyn-F was also significantly enhanced. In summary, an improved catalytic activity and thermostability of the design variant Xyn-F has been reported.

Characterization and rational engineering of an alkaline-tolerant azoreductase derived from Roseibium sp. H3510 for enhanced decolorization of azo dyes

rAzoR2326, an azoreductase derived from Roseibium sp. H3510, functions as an FMN-dependent homodimer utilizing NADH as cofactor. It demonstrated maximum activity at 45 °C and retained moderate activity above 50 °C, exhibiting stability from pH 7-10. Evolution and structure guided rational design of wild-type rAzoR2326 (WT) efficiently yielded 6 single-point mutants with improved thermostability and activity from a 22-variant library. Further combinatorial mutation led to mutant M20 with substantially enhanced thermostability (15-fold longer half-life at 50 °C) and activity (3.24-fold higher kcat/Km). M20 exhibited superior catalytic properties for decolorizing Allura Red compared to WT. Specifically, its decolorization capacity at pH 10.0 was 4.26-fold higher than WT. Additionally, M20 demonstrated remarkable thermostability, retaining 76.83 % decolorization activity for Allura Red after 120 min at 50 °C, whereas WT nearly lost all catalytic activity under the same conditions. Molecular dynamics simulations revealed the structural changes in M20, such as improved hydrogen bonding and a new C-H···π interaction, led to a more compact and rigid enzyme structure. This resulted in a more stable FMN-binding pocket and substrate tunnel, thereby improving the catalytic stability and activity of M20. Given its enhanced dye decolorization ability and alkaline tolerance, M20 shows promise as a biocatalyst for treating azo dye effluents.

Rational engineering of homospermidine synthase for enhanced catalytic efficiency toward spermidine synthesis

Spermidine is a naturally occurring polyamine widely utilized in the prevention and treatment of various diseases. Current spermidine biosynthetic methods have problems such as low efficiency and complex multi-enzyme catalysis. Based on sequence-structure-function relationships, we engineered the widely studied homospermidine synthase from Blastochloris viridis (BvHSS) and obtained mutants that could catalyze the production of spermidine from 1,3-diaminopropane and putrescine. The specific activities of BvHSS and the mutants D361E and E232D + D361E (E232D-D) were 8.72, 46.04 and 48.30 U/mg, respectively. The optimal pH for both mutants was 9.0, and the optimal temperature was 50 °C. Molecular docking and dynamics simulations revealed that mutating aspartic acid at position 361 to glutamic acid narrowed the substrate binding pocket, promoting stable spermidine production. Conversely, mutating glutamic acid at position 232 to aspartic acid enlarged the substrate channel entrance, facilitating substrate entry into the active pocket and enhancing spermidine generation. In whole-cell catalysis lasting 6 h, D361E and E232D-D synthesized 725.3 and 933.5 mg/L of spermidine, respectively. This study offers a practical approach for single-enzyme catalyzed spermidine synthesis and sheds light on the crucial residues influencing homospermidine synthase catalytic activity in spermidine production.

Biochemical identification of D-mannose 2-epimerase from Cytophagaceae bacterium SJW1-29 for efficient bioconversion of D-glucose to D-mannose

Enzymatic production of D-mannose attracts increasing attention because of the health effects and commercial values of D-mannose. Several kinds of epimerases or isomerases have been used for enzymatic production of D-mannose from D-glucose or D-fructose. D-Mannose epimerase (MEase), belonging to N-acyl-D-glucosamine 2-epimerase superfamily enzymes, catalyzes the C-2 epimerization between D-glucose and D-mannose. In this study, a novel MEase was identified from Cytophagaceae bacterium SJW1-29. Sequence and structure alignments indicate that it is highly conserved with the reported R. slithyformis MEase with the known crystal structure. It was a metal-independent enzyme, with an optimal pH of 8.0 and an optimal temperature of 40 °C. The specific activities on D-glucose and D-mannose were 2.90 and 2.96 U/mg, respectively. The Km, kcat, and kcat/Km on D-glucose were measured to be 194.9 mM, 2.72 s-1, and 0.014 mM-1 s-1, respectively. The purified enzyme produced 23.15 g/L of D-mannose from 100 g/L of D-glucose at pH 8.0 and 40 °C for 8 h, with a conversion rate of 23.15 %.

Computer-aided design to enhance the stability of aldo-keto reductase KdAKR

The aldo-keto reductase (AKR) KdAKR from Kluyvermyces dobzhanskii can reduce t-butyl 6-chloro-(5S)-hydroxy-3-oxohexanoate ((5S)-CHOH) to t-butyl 6-chloro-(3R,5S)-dihydroxyhexanoate ((3R,5S)-CDHH), which is the key chiral intermediate of rosuvastatin. Herein, a computer-aided design that combined the use of PROSS platform and consensus design was employed to improve the stability of a previously constructed mutant KdAKRM6 . Experimental verification revealed that S196C, T232A, V264I and V45L produced improved thermostability and activity. The "best" mutant KdAKRM10 (KdAKRM6 -S196C/T232A/V264I/V45L) was constructed by combining the four beneficial mutations, which displayed enhanced thermostability. Its T50 15 and Tm values were increased by 10.2 and 10.0°C, respectively, and half-life (t1/2 ) at 40°C was increased by 17.6 h. Additionally, KdAKRM10 demonstrated improved resistance to organic solvents compared to that of KdAKRM6 . Structural analysis revealed that the increased number of hydrogen bonds and stabilized hydrophobic core contributed to the rigidity of KdAKRM10 , thus improving its stability. The results validated the feasibility of the computer-aided design strategy in improving the stability of AKRs.

Structural and Functional Characterization of Obesumbacterium proteus Phytase: A Comprehensive In-Silico Study

Phytate, also known as myoinositol hexakisphosphate, exhibits anti-nutritional properties and possesses a negative environmental impact. Phytase enzymes break down phytate, showing potential in various industries, necessitating thorough biochemical and computational characterizations. The present study focuses on Obesumbacterium proteus phytase (OPP), indicating its similarities with known phytases and its potential through computational analyses. Structure, functional, and docking results shed light on OPP's features, structural stability, strong and stable interaction, and dynamic conformation, with flexible sidechains that could adapt to different temperatures or specific functions. Root Mean Square fluctuation (RMSF) highlighted fluctuating regions in OPP, indicating potential sites for stability enhancement through mutagenesis. The systematic approach developed here could aid in enhancing enzyme properties via a rational engineering approach. Computational analysis expedites enzyme discovery and engineering, complementing the traditional biochemical methods to accelerate the quest for superior enzymes for industrial applications.

Rational design for thermostability improvement of a novel PL-31 family alginate lyase from Paenibacillus sp. YN15

Currently, alginate oligosaccharides (AOS) become attractive due to their excellent physiological effects. AOS has been widely used in food, pharmaceutical, and cosmetic industries. Generally, AOS can be produced from alginate using alginate lyase (ALyase) as the biocatalyst. However, most ALyase display poor thermostability. In this study, a thermostable ALyase from Paenibacillus sp. YN15 (Payn ALyase) was characterized. It belonged to the polysaccharide lyase (PL) 31 family and displayed poly β-D-mannuronate (Poly M) preference. Under the optimum condition (pH 8.0, 55 °C, 50 mM NaCl), it exhibited maximum activity of 90.3 U/mg and efficiently degraded alginate into monosaccharides and AOS with polymerization (DP) of 2-4. Payn ALyase was relatively stable at 55 °C, but the thermostability dropped rapidly at higher temperatures. To further improve its thermostability, rational design mutagenesis was carried out based on a combination of FireProt, Consensus Finder, and PROSS analysis. Finally, a triple-point mutant K71P/Y129G/S213G was constructed. The optimum temperature was increased from 55 to 70 °C, and the Tm was increased from 62.7 to 64.1 °C. The residual activity after 30 min incubation at 65 °C was enhanced from 36.0 % to 83.3 %. This study provided a promising ALyase mutant for AOS industrial production.