A Novel and Simple Method for the Purification of Extracellular Levansucrase from Zymomonas mobilis

Molecular Docking Analysis and Biochemical Evaluation of Levansucrase from Sphingobium chungbukense DJ77

Bacterial exopolymer Levan (β-(2,6) polyfructan) synthesized by levansucrase has attracted interest for various applications due to its low intrinsic viscosity compared with other polysaccharides. We report a novel levansucrase (Lsc) isolated from Sphingobium chunbukense DJ77 and verify its biochemical characteristics by comparative analysis of molecular docking analysis (MOE) and catalytic residue analysis. The complete sequence of the Lsc encoding gene ( lsc) was cloned under the direction of the T7 promoter and purified in an Escherichia coli BL21 (DE3) protein expression system. The enzyme activity analysis and ligand docking MOE study of S. chungbukense DJ77 Lsc revealed that Arg 77, Ser112, Arg 195, Asp196, Glu257, and Gln275 were involved in the sucrose binding and splitting as well as transfructosylation activity. A catalytic comparison of Lsc of S. chungbukense DJ77 with the results of site-directed mutational analysis indicated that Gln275 may coordinate a favorable substrate binding environment, offering broad pH resistance in the range of 5-10. The results suggest that the recombinant E. coli carrying S. chungbukense DJ77 Lsc might produce levan under the regular growth conditions with less need for pH manipulation.

Effect of bacteria type and sucrose concentration on levan yield and its molecular weight

BACKGROUND

Levan has been traditionally produced from microorganism. However, there is a continuous effort in looking for new strains that improve levan production yield and uses alternative sugar sources for growth. Despite having a wide range of data about levan yield, there are not papers which allow controlling molecular weight, and that plays an essential role for further applications.

RESULTS

The effect of the sucrose concentration on levan yield (and its molecular weight) from Bacillus atrophaeus and Acinetobacter nectaris (Gram positive and Gram negative respectively) was studied in this work. It was found that A. nectaris growth (from 3 to 1.5 g L^-1 in 40 h) and its levan production (from 3 to 1.5 g L^-1) decreases by increasing sucrose concentration (best results at a concentration of 120 g L^-1) whereas B. atrophaeus growth (3.5 g L^-1 in 30 h) and its levan production (also 3.5 g L^-1) were not affected by modifying that parameter. Levan molecular weight from A. nectaris decreases by increasing sucrose concentration (from 8000 to 2000 kDa) whereas levan molecular weight from B. Atrophaeus remains always around 50 kDa. By performing a kinetic study, it was shown that A. nectaris growth follows a substrate-inhibition model, whereas Monod equation provided a good fit for B. atrophaeus growth. Finally, wastes from orange juice industry were used as a medium culture to cultivate those microorganism, obtaining good results with B. atrophaeus (growth 3 g L^-1 in 30 h).

CONCLUSIONS

Levan production kinetics was determined and compared between different bacteria types.

Purification and characterization of an intracellular levansucrase derived from Bacillus methylotrophicus SK 21.002

An intracellular levansucrase from Bacillus methylotrophicus SK 21.002 was isolated, purified, and characterized. The final specific levansucrase activity was 135.40 U/mg protein with an 11.78-fold enrichment and a 9.28% recovery rate. The molecular weight of the enzyme was approximately 60,000 Da as evaluated by gel filtration and SDS-PAGE. Both the maximum transfructosylation and hydrolytic activities were observed at pH 6.5. The enzyme exhibited optimum transfructosylation activity at 40 °C, whereas the optimum temperature of hydrolytic activity was 45 °C. Cu(2+), Fe(2+), Zn(2+), and Ni(2+) inhibited both the transfructosylation and hydrolytic activities up to 100%, whereas Mn(2+) inhibited only hydrolytic activity. Ca(2+) and Mg(2+) stimulated both transfructosylation and hydrolytic activities. The chemical modifiers (n-bromosuccinimide and phenylmethanesulfonyl fluoride) strongly inhibited hydrolytic and transfructosylation activity of the levansucrase. The Km and Vmax values of the purified levansucrase were 117.2 mM and 33.23 μmol/mg·Min, respectively. When the fructose concentration was below 0.2 M, higher fructose concentrations promoted the transfructosylation and inhibited the hydrolytic activity.

Properties of Geobacillus stearothermophilus levansucrase as potential biocatalyst for the synthesis of levan and fructooligosaccharides

The production of levansucrase (LS) by thermophilic Geobacillus stearothermophilus was investigated. LS production was more effective in the presence of sucrose (1%, w/v) than fructose, glucose, glycerol or raffinose. The results (Top 57°C; stable for 6 h at 47°C) indicate the high stability of the transfructosylation activity of G. stearothermophilus LS as compared with LSs from other microbial sources. Contrary to temperature, the pH had a significant effect on the selectivity of G. stearothermophilus LS-catalyzed reaction, favoring the transfructosylation reaction in the pH range of 6.0-6.5. The kinetic parameter study revealed that the catalytic efficiency of transfructosylation activity was higher as compared with the hydrolytic one. In addition to levan, G. stearothermophilus LS synthesized fructooligosaccharides in the presence of sucrose as the sole substrate. The results also demonstrated the wide acceptor specificity of G. stearothermophilus LS with maltose being the best fructosyl acceptor. This study is the first on the catalytic properties and the acceptor specificity of LS from G. stearothermophilus.

An influence of ethanol and temperature on products formation by different preparations of Zymomonas mobilis extracellular levansucrase

The ethanol and temperature effects on the ratio between Zymomonas mobilis 113S extracellular levansucrase activities were studied using fermentation broth supernatant, "levan-levansucrase" sediment precipitated by ethanol and highly purified enzyme. The fructooligosaccharide (FOS) production at different temperatures in the presence of ethanol was investigated. An ethanol increases FOS biosynthesis activity part of levansucrase. Especially, this effect was pronounced at lower temperatures (35-40 °C) and using purified levansucrase. The inverse relationship between temperature and ratio synthetic activity/total activity of levansucrase was found. The FOS composition containing mostly 1-kestose, 6-kestose, and neokestose obtained in the presence of different ethanol concentrations was found relative constant, while the changes in the sucrose concentration and temperature gave slight changes in the ratio between 1-kestose and 6-kestose.

Fully automated chip-based negative mode nanoelectrospray mass spectrometry of fructooligosaccharides produced by heterologously expressed levansucrase from Pseudomonas syringae pv. tomato DC3000

Pseudomonas syringae pathovars possess multiple levansucrases with still unclear specific roles for bacteria. We have cloned and expressed three levansucrase genes, lsc1, lsc2 and lsc3, from P. syringae DC3000 in Escherichia coli. Levansucrases synthesize a high molecular weight fructan polymer, levan, from sucrose and in the case of some levansucrases, fructooligosaccharides (FOS) with potential prebiotic effects are also produced. The ability of purified Lsc3 protein of DC3000 to synthesize FOS was tested using prolonged incubation time and varied concentrations of sugar substrates. Thin-layer chromatography (TLC) analysis of reaction products disclosed formation of FOS from both sucrose and raffinose, revealing a new catalytic property for P. syringae levansucrases. In order to analyze Lsc3-produced FOS in underivatized form, we optimized a novel method recently introduced in carbohydrate research, based on fully automated chip-based nanoelectrospray ionization (nanoESI) high-capacity ion trap mass spectrometry (HCT-MS). Uding chip-based nanoESI MS in negative ion mode, FOS, with degrees of polymerization up to five, were detected in reaction mixtures of Lsc3 with sucrose and raffinose. For confirmation, further structural analysis by tandem mass spectrometry (MS/MS) employing collision-induced dissociation at low energies was performed. To validate the method, commercial inulin-derived FOS preparations Orafti P95 and Orafti Synergy1, which are currently used as prebiotics, were used as controls. By chip-based nanoESI HCT-MS, similar FOS distribution was observed in these reference mixtures. Thereby, the obtained data allowed us to postulate that FOS produced by the Lsc3 protein of P. syringae DC3000 may be prebiotic as well.