A variant of Orpinomyces joyonii 1,3-1,4-beta-glucanase with increased thermal stability obtained by random mutagenesis and screening

Application of foam separation in production of β-glucanase in Pichia

β-glucanase is widely used in many fields and has great economic value and development space, but it faces the difficulties of separation and nutrient destruction in the process of industrial production. Foam separation is a simple, mild and efficient adsorption separation technique that enables efficient separation and extraction of β-glucanase. In this study, five single factors(loading volume, pH, separation gas velocity, fermentation loading concentration, surfactant concentration) of foam separation and harvest of β-glucanase produced by Pichia pastoris were studied. The best univariate condition was: 600 mL/min separation gas velocity, loading volume of 200 mL, initial enzyme concentration of 100 g/mL, surfactant concentration of 0.3 mg/mL and pH of 5. Based on the best univariate condition, the optimal separation conditions of β-glucanase were further explored, and the five-factor four-level orthogonal test was designed. From the experimental results, the best separation condition was: 600 mL/min, loading volume of 200 mL, initial enzyme concentration of 100 μg/mL, surfactant concentration of 0.5 mg/mL and pH of 5. Under this separation condition, the enrichment ratio (E) was 0.56 and the recovery rate (R) was 96.01%.

Improvement of enzyme activity of β-1,3-1,4-glucanase from Paenibacillus sp. X4 by error-prone PCR and structural insights of mutated residues

β-1,3-1,4-Glucanase (BGlc8H) from Paenibacillus sp. X4 was mutated by error-prone PCR or truncated using termination primers to improve its enzyme properties. The crystal structure of BGlc8H was determined at a resolution of 1.8 Å to study the possible roles of mutated residues and truncated regions of the enzyme. In mutation experiments, three clones of EP 2-6, 2-10, and 5-28 were finally selected that exhibited higher specific activities than the wild type when measured using their crude extracts. Enzyme variants of BG_2-6, BG_2-10, and BG_5-28 were mutated at two, two, and six amino acid residues, respectively. These enzymes were purified homogeneously by Hi-Trap Q and CHT-II chromatography. Specific activity of BG_5-28 was 2.11-fold higher than that of wild-type BG_wt, whereas those of BG_2-6 and BG_2-10 were 0.93- and 1.19-fold that of the wild type, respectively. The optimum pH values and temperatures of the variants were nearly the same as those of BG_wt (pH 5.0 and 40 °C, respectively). However, the half-life of the enzyme activity and catalytic efficiency (k _cat/K _m) of BG_5-28 were 1.92- and 2.12-fold greater than those of BG_wt at 40 °C, respectively. The catalytic efficiency of BG_5-28 increased to 3.09-fold that of BG_wt at 60 °C. These increases in the thermostability and catalytic efficiency of BG_5-28 might be useful for the hydrolysis of β-glucans to produce fermentable sugars. Of the six mutated residues of BG_5-28, five residues were present in mature BGlc8H protein, and two of them were located in the core scaffold of BGlc8H and the remaining three residues were in the substrate-binding pocket forming loop regions. In truncation experiments, three forms of C-terminal truncated BGlc8H were made, which comprised 360, 286, and 215 amino acid residues instead of the 409 residues of the wild type. No enzyme activity was observed for these truncated enzymes, suggesting the complete scaffold of the α₆/α₆-double-barrel structure is essential for enzyme activity.

Engineering of a thermostable β-1,3-1,4-glucanase from Bacillus altitudinis YC-9 to improve its catalytic efficiency

BACKGROUND

Error-prone polymerase chain reaction (PCR) is frequently used in directed evolution of enzymes to modify their quality. In this study, error-prone PCR was used to improve the catalytic efficiency of β-1,3-1,4-glucanase from Bacillus altitudinis YC-9.

RESULTS

By screening, the mutant Glu-3060 with higher activity was selected among 5000 transformants. After induction with isopropyl β-D-1-thiogalactopyranoside (IPTG), the activity of the mutant Glu-3060 reached 474.6 U mL(-1), resulting in a 48.6% increment of the parent enzyme activity. Research on the characterization of the mutated enzyme showed the optimal pH of the mutated enzyme to be 5.0, which is lower than the parent enzyme, but thermal stability was almost the same between them. Sequence analysis of the mutated enzyme revealed that three amino acids were changed compared with the parent enzyme, including K142N, Q203L and N214D.

CONCLUSION

The three-dimensional structure predicted by SWISS-MODEL of the mutated enzyme Glu-3060 showed that the substitution of three amino acids had an effect on the catalytic activity, stability and optimal pH of the enzyme, through changing the charge properties or electron density, forming secondary keys, the acidity of the amino acids and the side chain group. The sum effects of all the factors were increased activity of the mutated enzyme and decreased optimal pH, while the same thermostability was maintained, thereby increasing the suitability of the enzyme for industrial use.