Purification, kinetic and thermodynamic characterization of soluble acid invertase from sugarcane (Saccharum officinarum L.)

Sequential cultivation method for β-fructofuranosidase production from Aspergillus tamarii URM4634, evaluation of their biochemical and kinetic/thermodynamic characteristics, and application on sucrose hydrolysis

The present study focused on evaluating the sequential fermentation (SF) method for FFase production from Aspergillus tamarii URM4634 using soybean bran as substrate. The SF was performed using soybean bran as substrate at 72 h and 30 °C and the maximum hydrolytic activity (44.00 U mL-1), corresponding to an increase of 2.98-fold to about SmF using sucrose as substrate. Already the maximum transfructosylating activity was 26.10 U mL-1. The FFase presents maximum hydrolytic activity at pH 5.0-6.0 and transfructosylating at pH 6.0 and 60 °C for both enzyme activities. The enzyme showed a typical hydrolytic kinetic profile evidenced by more affinity by sucrose hydrolysis reaction than the fructosyl transfer one. From kinetic and thermodynamic data of thermal denaturation, it was observed that the enzyme presents suitable at 55 °C, evidenced by the large half-life (990.21 min) and D values (3289.41 min). The maximum release of reducing sugars (8.45 g L-1) was obtained in hydrolysis of 20% sucrose during 180 min. The results obtained for FFase production by SF proved that this method can be used satisfactorily for sucrose-degrading enzymes and can contribute to the development of the SF technique to produce different industrial-interest enzymes.

Kinetic/thermodynamic study of immobilized β-fructofuranosidase from Aspergillus tamarii URM4634 in chitosan beads and application on invert sugar production in packed bed reactor

β-fructofuranosidase (FFase) from Aspergillus tamarii URM4634 was immobilized covalently in chitosan beads. It was characterized biochemically, studied in terms of kinetic and thermodynamic parameters, and applied on conversion of sucrose for invert sugar production in a packed bed reactor (PBR). The optimum reactional conditions were determined and obtained at pH 5.0 and 60 °C. FFase was thermostable at 50-55°C. At 50°C, the enzyme shows longer half-life (t_1/2) (594.13 min) and a higher D-value (1,973.64 min). This indicates that immobilized FFase was stable at temperature commonly used in invert sugar production. The following thermodynamic parameters were obtained: activation energy (E*_d = 301.57 kJ mol^-1), enthalpy (298.76 ≤ ΔH*_d ≤ 298.89 kJ mol^-1), entropy (579.88 ≤ ΔS*_d ≤ 589.27 J K^-1 mol^-1) and Gibbs free energy (100.29 ≤ ΔG*_d ≤ 108.47 kJ mol^-1). The high E*_d, ΔH*_d and ΔG*_d values confirmed FFase thermostability. The high and positive values for ΔS*_d indicate an increase in disorder due opening of the enzyme structure. The sucrose hydrolysis in PBR showed a maximum invert sugar yield (96.0%) at 15 min of operation. The hydrolysis process remained efficient up to 100 min (70.22%). The results obtained in the present study provide a good indication that immobilized FFase on chitosan beads in PBR is efficient to invert sugar production for food industry.

Comparative evaluation of extracellular β-d-fructofuranosidase in submerged and solid-state fermentation produced by newly identified Bacillus subtilis strain

AIMS

To screen and identify a potential extracellular β-d-fructofuranosidase or invertase-producing bacterium from soil, and comparatively evaluate the enzyme biosynthesis under submerged and solid-state fermentation (SSF).

METHODS AND RESULTS

Extracellular invertase-producing bacteria were screened from soil. Identification of the potent bacterium was performed based on microscopic examinations and 16S rDNA molecular sequencing. Bacillus subtilis LYN12 invertase secretion was surplus with wheat bran humidified with molasses medium (70%), with elevated activity at 48 h and 37°C under SSF, whereas under submerged conditions, increased activity was observed at 24 h and 45°C in the molasses medium. The study revealed a simple fermentative medium for elevated production of extracellular invertase from a fast growing Bacillus strain.

CONCLUSIONS

Bacterial invertases are scarce and limited reports are available. By far, this is the first report on the comparative analysis of optimization of extracellular invertase synthesis from B. subtilis strain by submerged and SSF. The use of agricultural residues increased yields resulting in the development of a cost-effective and stable approach.

SIGNIFICANCE AND IMPACT OF THE STUDY

Bacillus subtilis LYN12 invertase possesses excellent fermenting capability to utilize agro-industrial residues under submerged and solid-state conditions. This could be a beneficial candidate in food and beverage processing industries.

Lactobacillus plantarum WCFS1 β-Fructosidase: Evidence for an Open Funnel-Like Channel Through the Catalytic Domain with Importance for the Substrate Selectivity

β-Fructosidase, a glycoside hydrolase of a biotechnologically important strain, was studied for its biochemical, physicochemical, and three-dimensional structure characteristics. This enzyme was heterologously expressed in Escherichia coli as a C-terminal His-tagged protein (SacB). β-Fructosidase catalyzes the cleavage of glycoside bonds toward certain carbohydrates with β-fructofuranosyl linkages; however, SacB exhibited selectivity toward sucrose and an optimum activity at pH 6.0-6.5 and 37 °C. In such optimum enzymatic activity conditions, the SacB was commonly observed as a monodisperse protein by dynamic light scattering (DLS). As β-fructosidase belongs to glycoside hydrolase family 32 (GH32), a β-sandwich and a five-bladed β-propeller domain are typical predicted folds in its structure. Docking and molecular dynamic simulations revealed for the first time a funnel-like channel perfectly exposed in the β-propeller domain of the Lactobacillus plantarum β-fructosidase (this allows the interaction between its entire catalytic triad and substrates that are larger than sucrose). In contrast, SacB showed a closed central tunnel collaterally induced by its His-tag.

Structural Analysis of the Catalytic Mechanism and Substrate Specificity of Anabaena Alkaline Invertase InvA Reveals a Novel Glucosidase

Invertases catalyze the hydrolysis of sucrose to glucose and fructose, thereby playing a key role in primary metabolism and plant development. According to the optimum pH, invertases are classified into acid invertases (Ac-Invs) and alkaline/neutral invertases (A/N-Invs), which share no sequence homology. Compared with Ac-Invs that have been extensively studied, the structure and catalytic mechanism of A/N-Invs remain unknown. Here we report the crystal structures of Anabaena alkaline invertase InvA, which was proposed to be the ancestor of modern plant A/N-Invs. These structures are the first in the GH100 family. InvA exists as a hexamer in both crystal and solution. Each subunit consists of an (α/α)₆ barrel core structure in addition to an insertion of three helices. A couple of structures in complex with the substrate or products enabled us to assign the subsites -1 and +1 specifically binding glucose and fructose, respectively. Structural comparison combined with enzymatic assays indicated that Asp-188 and Glu-414 are putative catalytic residues. Further analysis of the substrate binding pocket demonstrated that InvA possesses a stringent substrate specificity toward the α1,2-glycosidic bond of sucrose. Together, we suggest that InvA and homologs represent a novel family of glucosidases.

Characterization of a novel low-temperature-active, alkaline and sucrose-tolerant invertase

A glycoside hydrolase family 32 invertase from Bacillus sp. HJ14 was expressed in Escherichia coli. The purified recombinant enzyme (rInvHJ14) showed typical biochemical properties of low-temperature-active and alkaline enzymes: (i) rInvHJ14 was active and stable in the range of pH 7.0–9.5 with an apparent pH optimum of 8.0; (ii) rInvHJ14 was most active but not stable at 30–32.5 °C, with 19.7, 48.2 and 82.1% of its maximum activity when assayed at 0, 10 and 20 °C, respectively, and the E_a, ΔG^* (30 °C), K_m (30 °C) and k_cat (30 °C) values for hydrolysis of sucrose by rInvHJ14 was 47.6 kJ mol⁻¹, 57.6 kJ mol⁻¹, 62.9 mM and 746.2 s⁻¹, respectively. The enzyme also showed strong sucrose tolerance. rInvHJ14 preserved approximately 50% of its highest activity in the presence of 2045.0 mM sucrose. Furthermore, potential factors for low-temperature-active and alkaline adaptations of rInvHJ14 were presumed. Compared with more thermostable homologs, rInvHJ14 has a higher frequency of glycine residues and a longer loop but a lower frequency of proline residues (especially in a loop) in the catalytic domain. The catalytic pockets of acid invertases were almost negatively charged while that of alkaline rInvHJ14 was mostly positively charged.

Stimulation of extracellular invertase production from spent yeast when sugarcane pressmud used as substrate through solid state fermentation

Efforts were made to utilize the waste/by-product of two agro-process industries namely pressmud from sugar processing industries and spent yeast from distilleries manufacturing ethanol from cane molasses, for the production of microbial invertase. Our experimentation indicated that these two sources could be ideally utilized for the production of invertase through solid substrate fermentation (SSF). SSF with spent yeast had given highest specific activity of 430 U/mg in 72 h of fermentation. Inoculum percentage of yeast cells on pressmud was optimized as 50% (w/w) with a combination inoculum of spent yeast and fresh cultured yeast at a ratio of 7:3. Crude enzyme was characterized for optimum pH and temperature and maximum activity was recorded at pH 5.0 and at a temperature of 40°C. Impacts of metal ions and detergents on invertase action were studied in which Mn²⁺, Fe³⁺, Al³⁺ and detergents had enhanced the activity of the enzyme whereas Cu²⁺ and Zn²⁺ inhibited the enzyme activity. Purification of 9.8 folds was obtained by using three phase partition method.