Chemical modification results in hyperactivation and thermostabilization ofFusarium solaniglucoamylase

Biochemical Characterization of a Novel Thermostable 1,4-α-Glucoamylase from Aspergillus brasiliensis Strain Isolated in the Brazilian Atlantic Forest

Glucoamylases are exo-enzymes that cleave the ends of the starch chain, releasing glucose units. In the current work, we described a novel 1,4-α-glucoamylase from an A. brasiliensis strain isolated from an environmental sample. The purified glucoamylase, GlaAb, has a molecular mass of 69 kDa and showed a starch binding domain. GlaAb showed a similar sequence to other fungal glucoamylases, and the molecular 3D model analysis of GlaAb suggests an overall structure as described in the literature, except by elongation in the loop connecting the 4th and 5th α-helices. The enzyme showed activity over a wide range of pH and temperature, with maximum activity at pH 4.5 and 60 °C. GlaAb was stable at 50 °C for 7 h, maintaining 67% residual activity, and it was not inhibited by glucose up to 0.1 M. The glucoamylase was 65% more active in the presence of Mn2+ and showed a Km of 2.21 mg mL-1, Vmax of 155 U mg-1, Kcat 179 s-1, and Kcat/Km 81.06 mg mL-1 s-1 using potato starch as substrate. The results obtained are promising and provide the basis for the development of applications of GlaAb in the industrial process.

Investigation into the chemical modification of α-amylase using octenyl succinic anhydride: enzyme characterisation and stability studies

The present study describes the chemical modification of α-amylase using succinic anhydride (SA), phthalic anhydride (PA) and a novel modifier viz. 2-octenyl succinic anhydride (2-OSA). SA-, PA- and 2-OSA-α-amylases displayed a 50%, 91% and 46% increase in stability at pH 9, respectively; as compared to unmodified α-amylase. PA-α-amylase showed a significant increase in Ea and ΔH_a^#, and a concomitant decrease in ΔS_a^#. The modified α-amylases exhibited improved thermostability as reflected by significant reductions in K_d and ΔS_d^#, and increments in t_1/2, D-, E_d, ΔH_d^# and ΔG_d^# values. The modified α-amylases displayed variable stabilities in the presence of different surfactants, inhibitors, metal ions and organic solvents. Interestingly, the chemical modification was found to confer resistance against inactivation by Hg²⁺ on α-amylase. The conformational changes in modified α-amylases were investigated using intrinsic tryptophan fluorescence, ANS (extrinsic) tryptophan fluorescence, and dynamic fluorescence quenching. Both intrinsic and extrinsic tryptophan fluorescence spectra showed increased fluorescence intensity for the modified α-amylases. Chemical modification was found to induce a certain degree of structural rigidity to α-amylase, as shown by dynamic fluorescence quenching. Analysis of the CD spectra by the K2d method using the DichroWeb online tool indicated evident changes in the α-helix, β-sheet and random coil fractions of the α-amylase secondary structure, following chemical modification using anhydrides. PA-α-amylase exhibited the highest productivity in terms of hydrolysis of starch at 60 °C over a period of 5 h indicating potential in varied biotechnological applications.

Research progress of glucoamylase with industrial potential

Glucoamylase is one of the most widely used enzymes in industry, but the development background and existing circumstances of industrial glucoamylase were not described by published articles. CiteSpace, a powerful tool for bibliometric, was used to analyze the past, existing circumstances, and trends of a professional field. In this study, 1820 Web-of-Science-indexed articles from 1991 to 2021 were collected and analyzed by CiteSpace. The research hotspots of industrial glucoamylase, like glucoamylase strain directional improvement, Aspergillus niger glucoamylase, glucoamylase immobilization, application of glucoamylase in ethanol production, and "customized production" of porous starch, were found by analyzing countries, institutions, authors, keywords, and references of articles. PRACTICAL APPLICATIONS: The research progress of glucoamylase with industrial potential was analyzed by CiteSpace, and a significant research direction of glucoamylase with industrial potential was found. This is helpful for academic and corporate audiences to understand the current situation of glucoamylase with industrial potential and carry out follow-up works.

Chemically modified magnetic immobilized phospholipase A1 and its application for soybean oil degumming

In this paper, the free Phospholipase A₁ (PLA₁) was immobilized on a magnetic carrier. The average particle diameter of the magnetic carrier was 97 ± 1.3 nm, and the average particle diameter of the magnetically immobilized PLA₁ was 105 nm ± 1.3 nm. The enzyme activity was 1940.5 U/g. The magnetic enzyme was chemically modified with formaldehyde, dextran-aldehyde, and dextran-aldehyde-glycine. The proportions of primary amino groups in the modified magnetic immobilized enzyme PLA₁ were 0, 53.5% and 47.3%, respectively. The optimum pH of the enzyme after chemical modification was 6.5. When the system temperature was 60 °C, the magnetically immobilized PLA₁ modified with dextran-aldehyde-glycine had the optimal activity and stability. This chemically modified magnetic immobilized PLA₁ was applied to soybean oil degumming at 60 °C, 6.5 h (reaction time), and 0.10 mg/kg (enzyme dosage). The phosphorus content in the degummed oil was 9.2 mg/kg. The relative enzyme activity was 77.6% after 7 reuses which would be potentially advantageous for industrial applications.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at (10.1007/s13197-021-05017-4).

Chemical modification of enzymes to improve biocatalytic performance

Improvement in intrinsic enzymatic features is in many instances a prerequisite for the scalable applicability of many industrially important biocatalysts. To this end, various strategies of chemical modification of enzymes are maturing and now considered as a distinct way to improve biocatalytic properties. Traditional chemical modification methods utilize reactivities of amine, carboxylic, thiol and other side chains originating from canonical amino acids. On the other hand, noncanonical amino acid- mediated 'click' (bioorthogoal) chemistry and dehydroalanine (Dha)-mediated modifications have emerged as an alternate and promising ways to modify enzymes for functional enhancement. This review discusses the applications of various chemical modification tools that have been directed towards the improvement of functional properties and/or stability of diverse array of biocatalysts.

Carbonic anhydrase modification for carbon management

Carbonic anhydrase modification (chemical and biological) is an attractive strategy for its diverse application to accelerate the absorption of CO₂ from a flue gas with improved activity and stability. This article reports various possibilities of CA modification using metal-ligand homologous chemistry, cross-linking agents, and residue- and group-specific and genetic modifications, and assesses their role in carbon management. Chemically modified carbonic anhydrase is able to improve the absorption of carbon dioxide from a gas stream into mediation compounds with enhanced sequestration and mineral formation. Genetically modified CA polypeptide can also increase carbon dioxide conversion. Chemical modification of CA can be categorized in terms of (i) residue-specific modification (involves protein-ligand interaction in terms of substitution/addition) and group-specific modifications (based on the functional groups of the target CA). For every sustainable change, there should be no/limited toxic or immunological response. In this review, several CA modification pathways and biocompatibility rules are proposed as a theoretical support for emerging research in this area.

Design of combined crosslinked enzyme aggregates (combi-CLEAs) of β-galactosidase and glucose isomerase for the one-pot production of fructose syrup from lactose

A new bi-enzymatic catalyst has been produced by precipitation and crosslinking (combi-CLEAs) of β-galactosidase and glucose isomerase for catalyzing the cascade reactions of lactose conversion into fructose, producing a lactose-fructose syrup (LFS). Glucose isomerase was chemically aminated to increase its reactive surface groups for favour the crosslinking step. The effect of β-galactosidase to glucose isomerase activity ratio and glutaraldehyde to protein mass ratio in combi-CLEAs production was evaluated. The selected combi-catalyst was successfully used in the production of fructose syrup from lactose in a single reaction vessel. The biocatalyst could be used at least in five sequential batches of LFS production, remaining fully stable after a total of 50 h of reaction, obtaining a product of constant quality. A robust bi-enzymatic catalyst was produced that can be repeatedly used in LFS production, an attractive mild sweetener for the dairy food industry.

Improving the catalytic, kinetic and thermodynamic properties of Bacillus subtilis KU710517 milk clotting enzyme via conjugation with polyethylene glycol

Milk clotting enzyme (MCE) produced by Bacillus subtilis KU710517 was conjugated to several activated polysaccharides. Among all the conjugates, the enzyme conjugated with polyethylene glycol (PEG) exhibited the highest retained activity (551U/mg protein) with a recovered activity of 95.3%. The activation energy of PEG-conjugated enzyme was calculated as 24.56kJ·mol^-1which was lower than that of the native one (29.27kJ·mol^-1) however, the temperature quotient (Q₁₀) was about 1.08 for the two forms of the enzyme. The calculated half-life times of PEG-conjugated enzyme at 55 and 60°C were 317.78 and 128.6min respectively, whereas at the same temperatures the native enzyme had lower half-life times (53 and 19.6min respectively). The data of thermodynamic analysis for substrate catalysis including the specificity constant (V_max/K_m), turnover number (k_cat), catalytic efficiency (k_cat/K_m), enthalpy of activation (ΔH*), free energy of activation (ΔG*), free energy for transition state formation ΔG*_E-T and free energy of substrate binding ΔG*_E-S were determined for both native and PEG-conjugated enzyme. In addition, the thermodynamic parameters for irreversible inactivation (ΔH, ΔG, ΔS) were evaluated. The calculated results indicated that the catalytic properties after the PEG-conjugation were significantly improved.

Catalytic, kinetic and thermodynamic properties of stabilized Bacillus stearothermophilus alkaline protease

Bacillus stearothermophilus alkaline protease was conjugated to several oxidized polysaccharides of different chemical structure. The conjugates were evaluated for the kinetic and thermodynamic stability. The conjugated enzyme with oxidized pectin had the highest retained activity (79.5%) and the highest half-life (T_1/2) at 50°C and pH 9.0. Compared to the native protease, the conjugated preparation exhibited lower activation energy (E_a), lower deactivation constant rate (k_d), higher T_1/2, and higher D values (decimal reduction time) within the temperature range of 50-60°C. The thermodynamic parameters for irreversible inactivation of native and conjugated protease indicated that conjugation significantly decreased entropy (ΔS*) and enthalpy (ΔH*) of deactivation. The calculated value of activation energy for thermal denaturation (E_ad) for the conjugated enzyme was 20.4KJmole^-1 higher over the native one. The results of thermodynamic analysis for substrate hydrolysis indicated that the enthalpy of activation (ΔH*) and free energy of activation (free energy of substrate binding) ΔG*_E-S and (ΔG*), (free energy of transition state) ΔG*_E-T values were lower for the modified protease. Similarly, there was significant improvement of k_cat, k_cat/K_m values. The enzyme proved to be metalloprotease and significantly stimulated by Ca²⁺ and Mg²⁺ whereas Hg²⁺, Fe³⁺ Cu²⁺ and Zn²⁺ inhibited the enzyme activity. There was no pronounced effect on substrate specificity after conjugation.

Amination of enzymes to improve biocatalyst performance: coupling genetic modification and physicochemical tools

Improvement of the features of an enzyme is in many instances a pre-requisite for the industrial implementation of these exceedingly interesting biocatalysts.