Rational Substitution of Surface Acidic Residues for Enhancing the Thermostability of Thermolysin

Engineering of Glycosyltransferase for Efficient Biosynthesis of Salidroside

Salidroside has been widely used in the cosmetic and medicinal industries. Previously, potential glycosyltransferase UGTBS was obtained for salidroside synthesis. However, the catalytic efficiency for salidroside was undesirable. In this study, a semirational design was applied to engineer UGTBS. The quadruple mutant M4 (I62N/S129T/F168W/Y316S) showed significantly enhanced salidroside synthesis. A conversion rate of 94.7% was obtained using mutant M4, which was 2.2-fold higher than that of the wild-type. The regioselectivity of mutant M4 toward tyrosol hydroxyl was also improved, resulting in 97.9% salidroside in the total product, which was 1.2-fold higher than that of the wild type. Kinetic constants and molecular simulations indicated that increased affinity and altered conformation of the binding pocket accounted for the enhanced salidroside synthesis. Furthermore, a fed-batch cascade reaction strategy was used, and over 183 mM salidroside was obtained. The engineered mutant M4 demonstrated precise catalysis for salidroside formation.

Application of molecular dynamics simulation in the field of food enzymes: improving the thermal-stability and catalytic ability

Enzymes can produce high-quality food with low pollution, high function, high acceptability, and medical aid. However, most enzymes, in their native form, do not meet the industrial requirements. Sequence-based and structure-based methods are the two main strategies used for enzyme modification. Molecular Dynamics (MD) simulation is a sufficiently comprehensive technology, from a molecular perspective, which has been widely used for structure information analysis and enzyme modification. In this review, we summarize the progress and development of MD simulation, particularly for software, force fields, and a standard procedure. Subsequently, we review the application of MD simulation in various food enzymes for thermostability and catalytic improvement was reviewed in depth. Finally, the limitations and prospects of MD simulation in food enzyme modification research are discussed. This review highlights the significance of MD simulation and its prospects in food enzyme modification.

Improvement in organic solvent resistance of keratinase BLk by directed evolution

Keratinase, a vital enzyme in hair degradation, requires enhanced stability for industrial applications in the harsh reaction environment used for keratin hydrolysis. Previous studies have focused on improving keratinase thermostability. In this study, directed evolution was applied to enhance the organic solvent stability of the keratinase BLk from Bacillus licheniformis. Three mutants were identified, exhibiting significant enhanced stability in various solvents, although no similar improvements were observed in terms of thermostability. The identified mutations were located on the enzyme surface. The half-lives of the D41A, A24E, and A24Q mutants increased by 47-, 63-, and 61-fold, respectively, in the presence of 50% (v/v) acetonitrile compared to that of the wild type (WT). Similarly, in the presence of 50% (v/v) acetone, the half-lives of these mutants increased by 22-, 27-, and 27-fold compared to that of the WT enzyme. Notably, the proteolytic activity of all the selected mutants was similar to that of the WT enzyme. Furthermore, molecular dynamics simulation was used to assess the possible reasons for enhanced solvent stability. These results suggest that heightened intramolecular interactions, such as hydrogen bonding and hydrophobic interactions, contribute to improved solvent tolerance. The mutants obtained in this study hold significant potential for industrial applications.

Improving the Thermostability of Serine Protease PB92 from Bacillus alcalophilus via Site-Directed Mutagenesis Based on Semi-Rational Design

Proteases have been widely employed in many industrial processes. In this work, we aimed to improve the thermostability of the serine protease PB92 from Bacillus alcalophilus to meet the high-temperature requirements of biotechnological treatments. Eight mutation sites (N18, S97-S101, E110, and R143) were identified, and 21 mutants were constructed from B-factor comparison and multiple sequence alignment and expressed via Bacillus subtilis. Among them, fifteen mutants exhibited increased half-life (t1/2) values at 65 °C (1.13-31.61 times greater than that of the wild type). Based on the composite score of enzyme activity and thermostability, six complex mutants were implemented. The t1/2 values of these six complex mutants were 2.12-10.05 times greater than that of the wild type at 65 °C. In addition, structural analysis revealed that the increased thermal stability of complex mutants may be related to the formation of additional hydrophobic interactions due to increased hydrophobicity and the decreased flexibility of the structure. In brief, the thermal stability of the complex mutants N18L/R143L/S97A, N18L/R143L/S99L, and N18L/R143L/G100A was increased 4-fold, which reveals application potential in industry.

Thermostability enhancement and insight of L-asparaginase from Mycobacterium sp. via consensus-guided engineering

Acrylamide alleviation in food has represented as a critical issue due to its neurotoxic effect on human health. L-Asparaginase (ASNase, EC 3.5.1.1) is considered a potential additive for acrylamide alleviation in food. However, low thermal stability hinders the application of ASNase in thermal food processing. To obtain highly thermal stable ASNase for its industrial application, a consensus-guided approach combined with site-directed saturation mutation (SSM) was firstly reported to engineer the thermostability of Mycobacterium gordonae L-asparaginase (GmASNase). The key residues Gly97, Asn159, and Glu249 were identified for improving thermostability. The combinatorial triple mutant G97T/N159Y/E249Q (TYQ) displayed significantly superior thermostability with half-life values of 61.65 ± 8.69 min at 50 °C and 5.12 ± 1.66 min at 55 °C, whereas the wild-type was completely inactive at these conditions. Moreover, its T_m value increased by 8.59 °C from parent wild-type. Interestingly, TYQ still maintained excellent catalytic efficiency and specific activity. Further molecular dynamics and structure analysis revealed that the additional hydrogen bonds, increased hydrophobic interactions, and favorable electrostatic potential were essential for TYQ being in a more rigid state for thermostability enhancement. These results suggested that our strategy was an efficient engineering approach for improving fundamental properties of GmASNase and offering GmASNase as a potential agent for efficient acrylamide mitigation in food industry. KEY POINTS: • The thermostability of GmASNase was firstly improved by consensus-guided engineering. • The half-life and T_m value of triple mutant TYQ were significantly increased. • Insight on improved thermostability of TYQ was revealed by MD and structure analysis.

Identification and characterization of thermostable endo-polygalacturonase II B from Aspergillus luchuensis

Endo-polygalacturonase II B (PgaB) from Aspergillus luchuensis was orthologous to endo-polygalacturonase from Aspergillus niger with mutant sites Thr42Ser and Glu52Ala. Mature pgaB gene was cloned from the genomic DNA of A. luchuensis and secreted expressed with over 90% purity in Pichia Pastoris and reached 1.0 g/L after 144 hr culture. The recombinant PgaB was further purified by Ni-NTA chromatography. Using polygalacturonic acid (PGA) as substrate, the optimal condition for PgaB activity was 40°C and pH 4.5, respectively. Km and Vmax of PgaB were 0.19 mmol/l and 103.58 μmol min^-1  mg^-1 , respectively. The relative activity of PgaB remained more than 60% and 40% of maximum activity at 50 and 60°C for 7 hr. PgaB increased the light transmittance by 85% and showed high efficiency in juice clarification. The main product was galacturonic acid oligosaccharides with degrees of polymers (DP) 1-3. The PgaB is a potential pectinolytic enzyme in food industries. PRACTICAL APPLICATIONS: Endo-polygalacturonase II B (PgaB) was identified from Aspergillus luchuensis, a filamentous fungus widely used in food and beverage fermentation in East Asia. PgaB still kept its most activity at 60°C for 7 hr. Polygalacturonic acid (PGA) can be digested effectively by the PgaB and the main products are galacturonic acid oligosaccharides with degrees of polymers (DP) 1-3. PgaB shows high efficiency in juice clarification. The PgaB is a potential pectinolytic enzyme for the applications in food industries.

Enhancement of the thermostability of Aspergillus niger α-l-rhamnosidase based on PoPMuSiC algorithm

α-l-Rhamnosidase is a biotechnologically important enzyme in food industry and in the preparation of drugs and drug precursors. To expand the functionality of our previously cloned α-l-rhamnosidase from Aspergillus niger JMU-TS528, 14 mutants were constructed based on the changes of the folding free energy (ΔΔG), predicted by the PoPMuSiC algorithm. Among them, six single-site mutants displayed higher thermal stability than wild type (WT). The combinational mutant K573V-E631F displayed even higher thermostability than six single-site mutants. The spectra analyses displayed that the WT and K573V-E631F had almost similar secondary and tertiary structure profiles. The simulated protein structure-based interaction analysis and molecular dynamics calculation were further implemented to assess the conformational preferences of the K573V-E631F. The improved thermostability of mutant K573V-E631F may be attributed to the introduction of new cation-π and hydrophobic interactions, and the overall improvement of the enzyme conformation. PRACTICAL APPLICATIONS: The stability of enzymes, particularly with regards to thermal stability remains a critical issue in industrial biotechnology and industrial processing generally tends to higher ambient temperature to inhibit microbial growth. Most of the α-l-rhamnosidases are usually active at temperature from 30 to 60°C, which are apt to denature at temperatures over 60°C. To expand the functionality of our previously cloned α-l-rhamnosidase from Aspergillus niger JMU-TS528, we used protein engineering methods to increase the thermal stability of the α-l-rhamnosidase. Practically, conducting reactions at high temperatures enhances the solubility of substrates and products, increases the reaction rate thus reducing the reaction time, and inhibits the growth of contaminating microorganisms. Thus, the improvement on the thermostability of α-l-rhamnosidase on the one hand can increase enzyme efficacy; on the other hand, the high ambient temperature would enhance the solubility of natural substrates of α-l-rhamnosidase, such as naringin, rutin, and hesperidin, which are poorly dissolved in water at room temperature. Protein thermal resistance is an important issue beyond its obvious industrial importance. The current study also helps in the structure-function relationship study of α-l-rhamnosidase.

Improving the thermostability by introduction of arginines on the surface of α-L-rhamnosidase (r-Rha1) from Aspergillus niger

To improve the thermostability of α-L-rhamnosidase (r-Rha1), an enzyme previously identified from Aspergillus niger JMU-TS528, multiple arginine (Arg) residues were introduced into the r-Rha1 sequence to replace several lysine (Lys) residues that located on the surface of the folded r-Rha1. Hinted by in silico analysis, five surface Lys residues (K134, K228, K406, K440, K573) were targeted to produce a list of 5 single-residue mutants and 4 multiple-residue mutants using site-directed mutagenesis. Among these mutants, a double Lys to Arg mutant, i.e. K406R/K573R, showed the best thermostability improvement. The half-life of this mutant's enzyme activity increased 3 h at 60 °C, 23 min at 65 °C, and 3.5 min at 70 °C, when compared with the wild type. The simulated protein structure based interaction analysis and molecular dynamics calculation indicate that the thermostability improvement of the mutant K406R-K573R was possibly due to the extra hydrogen bonds, the additional cation-π interactions, and the relatively compact conformation. With the enhanced thermostability, the α-L-rhamnosidase mutant, K406R-K573R, has potentially broadened the r-Rha1 applications in food processing industry.

Development and characterization of an α-l-rhamnosidase mutant with improved thermostability and a higher efficiency for debittering orange juice

The glycoside hydrolase, α-l-rhamnosidase, could remove the bitter taste of naringin from citrus juices. However, most α-l-rhamnosidases are easily deactivated at high temperatures, limiting the practice in debittering citrus juices. The V529A mutant of the α-l-rhamnosidase r-Rha1 from Aspergillus niger JMU-TS528 was developed with improved thermostability using directed evolution technology and site-directed mutagenesis. The enzyme mutant had a half-live of thermal inactivation T_(1/2) of 1.92 h, 25.00 min, and 2 min at 60, 65, and 70 °C, respectively. In addition, it had improved substrate affinity and better resistance to the inhibition of glucose. The improved substrate affinity was related to its lowered binding energy. Most significantly, the naringin content was reduced to below the bitter taste threshold by treatment with 75 U/mL of the mutant during the preheating process of orange juice production. The comprehensive results indicate that thermostability improvement could promote the practical value of α-l-rhamnosidase in citrus juice processing.

Modulating Mobility: a Paradigm for Protein Engineering?

Proteins are highly mobile structures. In addition to gross conformational changes occurring on, for example, ligand binding, they are also subject to constant thermal motion. The mobility of a protein varies through its structure and can be modulated by ligand binding and other events. It is becoming increasingly clear that this mobility plays an important role in key functions of proteins including catalysis, allostery, cooperativity, and regulation. Thus, in addition to an optimum structure, proteins most likely also require an optimal dynamic state. Alteration of this dynamic state through protein engineering will affect protein function. A dramatic example of this is seen in some inherited metabolic diseases where alternation of residues distant from the active site affects the mobility of the protein and impairs function. We postulate that using molecular dynamics simulations, experimental data or a combination of the two, it should be possible to engineer the mobility of active sites. This may be useful in, for example, increasing the promiscuity of enzymes. Thus, a paradigm for protein engineering is suggested in which the mobility of the active site is rationally modified. This might be combined with more "traditional" approaches such as altering functional groups in the active site.

Protein thermostability engineering

Using structure and sequence based analysis we can engineer proteins to increase their thermal stability.