Engineering Site 228 of Streptomyces coelicolor Laccase for Optimizing Catalytic Activity

Engineering of Bacillus Laccase frL103 for Highly Efficient Degradation of Aflatoxin B1

Aflatoxin B1 (AFB1) is a highly toxic mycotoxin that poses significant risks to food safety and public health. Bacillus laccases have shown potential for degrading AFB1, but their catalytic efficiency remains suboptimal. This study explores the structure-function relationship of Bacillus vallismortis laccase frL103 by employing molecular modeling, site-directed mutagenesis, and molecular dynamics (MD) simulations. Eight key amino acid residues in the substrate binding pocket of frL103 were selected for alanine mutagenesis. After the enzymatic properties were evaluated, site 418, a loop region near the T1 copper, was subjected to saturation mutagenesis. Site saturation mutation at T418 identified the T418A and T418S as exhibiting the highest AFB1 degradation rate, with values of 56.7 and 53.6%, 1.24 and 1.17 times higher than WT (45.7%), respectively. MD simulations showed that these mutations did not significantly affect the overall structural stability of the enzyme but changed the flexibility and hydrogen bond interactions of the loop in which they were located, thereby helping to improve substrate binding and degradation. This study provides valuable insights into the structural mechanisms underlying the enhanced degradation of AFB1 and offers a basis for designing more efficient laccase mutants for bioremediation applications.

Enhancement in the Catalytic Properties of CotA Laccase from Bacillus pumilus via High-Throughput Screening Using Malachite Green as a Pressure

Bacterial laccase exhibits substantial application potential in various fields. In this study, we constructed a mutation library of CotA laccase from Bacillus pumilus using error-prone PCR, and we performed four rounds of enrichment screening under malachite green (MG) pressure. The results demonstrated that the proportions of the four selected mutant strains were significantly increased. The enzyme activities of the four final mutants PW2, PW5, PW4G, and PW6 were 94.34, 75.74, 100.66, and 87.04 U/mg, respectively, representing a significant increase of approximately 2- to 3-fold compared to the wild-type CotA laccase. Notably, PW4 exhibited significantly improved thermal stability at 90 °C and pH tolerance at pH 12.0. Homology modeling analysis revealed that alterations in the amino acid sequence rendered the spatial structure of the enzyme's catalytic site more favorable for substrate binding. For instance, the substitution of T262A in PW2 and V426I in PW4 shortened the side chains of the amino acids, thereby enlarging the substrate-binding cavity. The G382D mutation in PW2 and PW5 may induce altered protein conformation via spatial steric hindrance or electrostatic interactions, consequently impacting enzyme activity and stability. These findings provide valuable insights for enhancing the industrial application of bacterial laccase.

Enhanced thermostability and catalytic activity for arginine deiminase from Enterobacter faecalis SK32.001 via combinatorial mutagenesis

Arginine deiminase (ADI) exhibits potential for clinical and industrial applications, yet its low thermostability and catalytic efficiency under physiological conditions limit its utility. In this work, the ADI of Enterococcus faecalis SK32.001 was rationally designed. A total of 120 combinatorial mutants, ranging from two-point to six-point mutations, were constructed by sequentially stacking single-point positive mutants (F44W, N163P, E220L, N318E, A336G, T340I). Among them, the mutants S604, S700, S601, and S606 exhibited higher Tm values, while the mutants S605, S547, S602, S607, S517, and S557 demonstrated enhanced enzymatic activity. Notably, the five-point mutant S547 (F44W/N163P/E220I/A336G/T340I) exhibited remarkable pH tolerance (pH 4.5-9.5, with over 80 % residual enzyme activity). Its specific enzyme activity reached 131.60 U/mg, which was 2-fold higher than that of wild enzyme. The Tm value of this enzyme increases to 64.04 °C, 11.62 °C higher than that of the wild-type enzyme. The structure predicted by AlphaFold 2 revealed that the increased rigidity, formation of new hydrogen bonds, and an increase in hydrophobic residues may account for the enhanced enzyme activity and thermostability. This research demonstrates that rational design strategies can effectively optimize enzyme properties, providing insights for the development of microbial enzymes with industrial relevance.