High thermostability is required for alkaline ␣-amylases to maintain high catalytic activity under the harsh conditions used in textile production. In this study, we attempted to improve the thermostability of an alkaline ␣-amylase from Alkalimonas amylolytica through in silico rational design and systems engineering of disulfide bridges in the catalytic domain. Specifically, 7 residue pairs (P35-G426, Q107-G167, G116-Q120, A147-W160, G233-V265, A332-G370, and R436-M480) were chosen as engineering targets for disulfide bridge formation, and the respective residues were replaced with cysteines. Three single disulfide bridge mutants-P35C-G426C, G116C-Q120C, and R436C-M480C-of the 7 showed significantly enhanced thermostability. Combinational mutations were subsequently assessed, and the triple mutant P35C-G426C/G116C-Q120C/R436C-M480C showed a 6-fold increase in half-life at 60°C and a 5.2°C increase in melting temperature compared with the wild-type enzyme. Interestingly, other biochemical properties of this mutant also improved: the optimum temperature increased from 50°C to 55°C, the optimum pH shifted from 9.5 to 10.0, the stable pH range extended from 7.0 to 11.0 to 6.0 to 12.0, and the catalytic efficiency (k cat /K m ) increased from 1.8 ؋ 10 4 to 2.4 ؋ 10 4 liters/g · min. The possible mechanism responsible for these improvements was explored through comparative analysis of the model structures of wild-type and mutant enzymes. The disulfide bridge engineering strategy used in this work may be applied to improve the thermostability of other industrial enzymes.

In this study, the thermostability of an alkaline α-amylase from Alkalimonas amylolytica was significantly improved through structure-based rational and the introduction of multiple arginines (Arg) on the protein surface. Based on an analysis of the tertiary structure, seven residues (glutamine (Gln) 166, Gln 169, serine (Ser) 270, lysine (Lys) 315, Gln 327, asparagine (Asn) 346, and Asn 423) were selected as engineering targets and individually replaced with arginine. Five of the seven single-mutated enzymes-S270R, K315R, Q327R, N346R, and N423R-showed enhanced thermostability. Multiple arginines were subsequently introduced on the protein surface, and the quintuple-mutated enzyme S270R/K315R/Q327R/N346R/N423R showed a 6.4-fold improvement in half-life at 60 and a 5.4 °C increase in melting temperature (T m) compared with those of wild-type enzyme. Concomitantly, the optimal temperature, optimal pH, and catalytic efficiency of this mutated enzyme also improved. The mutated enzyme displayed a large shift in optimal pH from 9.5 to 11.0. In addition, the optimum temperature increased from 50 to 55 °C, and the catalytic efficiency (k cat/K m) increased from 1.8 × 10(4) to 3.6 × 10(4) L/(g · min). The intramolecular interactions of mutated enzymes that contributed to increased thermostability were examined through comparative analysis of the model structures of wild-type and mutated enzymes. The thermostable mutated enzymes generated in this study have potential applications in the textile industry.

The results may provide a theoretical basis for the application of EGCG oxidation using laccase and provide a novel technique for obtaining high production of tea pigments.

This study aimed to improve the thermostability of alkaline α-amylase from Alkalimonas amylolytica through structure-based rational design and systems engineering of its catalytic domain. Separate engineering strategies were used to increase alkaline α-amylase thermostability: (1) replace histidine residues with leucine to stabilize the least similar region in domain B, (2) change residues (glycine, proline, and glutamine) to stabilize the highly conserved α-helices in domain A, and (3) decrease the free energy of folding predicted by the PoPMuSiC program to stabilize the overall protein structure. A total of 15 single-site mutants were obtained, and four mutants - H209L, Q226V, N302W, and P477V - showed enhanced thermostability. Combinational mutations were subsequently introduced, and the best mutant was triple mutant H209L/Q226V/P477V. Its half-life at 60 °C was 3.8-fold of that of the wild type and displayed a 3.2 °C increase in melting temperature compared with that of the wild type. Interestingly, other biochemical properties of this mutant also improved: the optimum temperature increased from 50 °C to 55 °C, the optimum pH shifted from 9.5 to 10.0, the stable pH range expanded from 7.0-11.0 to 6.0-12.0, the specific activity increased by 24 %, and the catalytic efficiency (k cat/K m) increased from 1.8×10(4) to 3.5 × 10(4) l/(g min). Finally, the mechanisms responsible for the increased thermostability were analyzed through comparative analysis of structure models. The structure-based rational design and systems engineering strategies in this study may also improve the thermostability of other industrial enzymes.