Secretory expression and fermentation optimization for extracellular production of pullulanase in Vibrio natriegens / 生物工程学报

Pullulanase is a starch debranching enzyme, which is difficult in secretory expression due to its large molecular weight. Vibrio natriegens is a novel expression host with excellent efficiency in protein synthesis. In this study, we achieved secretory expression of the full-length pullulanase PulA and its truncated mutant PulN2 using V. natriegens VnDX strain. Subsequently, we investigated the effects of signal peptide, fermentation temperature, inducer concentration, glycine concentration and fermentation time on the secretory expression. Moreover, the extracellular enzyme activities of the two pullulanases produced in V. natriegens VnDX and E. coli BL21(DE3) were compared. The highest extracellular enzyme activity of PulA and PulN2 in V. natriegens VnDX were 61.6 U/mL and 64.3 U/mL, which were 110% and 62% that of those in E. coli BL21(DE3), respectively. The results indicated that V. natriegens VnDX can be used for secretory expression of the full-length PulA with large molecular weight, which may provide a reference for the secretory expression of other large molecular weight proteins in V. natriegens VnDX.

Advances in heterologous expression, structural elucidation and molecular modification of pullulanase / 生物工程学报

Starch is composed of glucose units linked by α-1, 4-glucoside bond and α-1, 6-glucoside bond. It is the main component of foods and the primary raw material for starch processing industry. Pullulanase can effectively hydrolyze the α-1, 6-glucoside bond in starch molecules. Combined with other starch processing enzymes, it can effectively improve the starch utilization rate. Therefore, it has been widely used in the starch processing industry. This paper summarized the screening of pullulanase-producing strain and its encoding genes. In addition, the effects of expression elements and fermentation conditions on the production of pullulanase were summarized. Moreover, the progress in crystal structure elucidation and molecular modification of pullulanase was discussed. Lastly, future perspectives on pullulanase research were proposed.

Improving the expression of recombinant pullulanase by increasing mRNA stability in Escherichia coli

Background: Pullulanase production in both wild-type strains and recombinantly engineered strains remains low. The Shine-Dalgarno (SD) sequence and stem-loop structure in the 5' or 3' untranslated region (UTR) are well-known determinants of mRNA stability. This study investigated the effect of mRNA stability on pullulanase heterologous expression. Results: We constructed four DNA fragments, pulA, SD-pulA, pulA-3t, and SD-pulA-3t, which were cloned into the expression vector pHT43 to generate four pullulanase expression plasmids. The DNA fragment pulA was the coding sequence (CDS) of pulA in Klebsiella variicola Z-13. SD-pulA was constructed by the addition of the 5' SD sequence at the 5' UTR of pulA. pulA-3t was constructed by the addition of a 3' stem-loop structure at the 3' UTR of pulA. SD-pulA-3t was constructed by the addition of the 5' SD sequence at the 5' UTR and a 3' stem-loop structure at the 3' UTR of pulA. The four vectors were transformed into Escherichia coli BL21(DE3). The pulA mRNA transcription of the transformant harboring pHT43-SD-pulA-3t was 338.6%, 34.9%, and 79.9% higher than that of the other three transformants, whereas the fermentation enzyme activities in culture broth and intracellularly were 107.0 and 584.1 times, 1.2 and 2.0 times, and 62.0 and 531.5 times the amount of the other three transformants (pulA, SD-pulA, and pulA-3 t), respectively. Conclusion: The addition of the 5' SD sequence at the 5' UTR and a 3' stem-loop structure at the 3' UTR of the pulA gene is an effective approach to increase pulA gene expression and fermentation enzyme activity.

Highly efficient enzymatic preparation of isomalto-oligosaccharides from starch using an enzyme cocktail

Background: Current commercial production of isomalto-oligosaccharides (IMOs) commonly involves a lengthy multistage process with low yields. Results: To improve the process efficiency for production of IMOs, we developed a simple and efficient method by using enzyme cocktails composed of the recombinant Bacillus naganoensis pullulanase produced by Bacillus licheniformis, α-amylase from Bacillus amyloliquefaciens, barley bran ß-amylase, and α-transglucosidase from Aspergillus niger to perform simultaneous saccharification and transglycosylation to process the liquefied starch. After 13 h of reacting time, 49.09% IMOs (calculated from the total amount of isomaltose, isomaltotriose, and panose) were produced. Conclusions: Our method of using an enzyme cocktail for the efficient production of IMOs offers an attractive alternative to the process presently in use.

Extraction, Purification and Characterization of Endo-Acting Pullulanase Type I from White Edible Mushrooms.

Pullulanase (EC 3.2.1.41) has been isolated and purified from white edible mushrooms by ammonium sulphate precipitation (20-70%) followed by ion exchange chromatography (DEAE-cellulose) and gel filtration (Sephadex G 75-120), with final yield (20%) and purification fold (17.8). The molecular mass of pullulanase enzyme was 112 kDa as estimated by SDS-PAGE and the pI value was 6.2. The apparent Km and Vmax values for purified pullulanse on pulluan were 0.27 mM and 0.74 μM min-1 respectively. The activity was optimum at 40○C and pH 6. Pullulanase showed moderate thermo-stability. A relative substrate specificity for hydrolysis of soluble starch, amylopectin and glycogen was 80, 60 and 30% respectively. Enzyme activity was highly activated by Fe+2, Mn+2 and Ca+2 ions, while the activity was inhibited by Hg+2 and Ag+ ions. Ethylenediaminetetraacetic acid (EDTA) and Dithiothreitol (DTT) were activated the enzyme activity. On contarary iodoacetate and sodium fluoride were inhibited the activity. HPTLC (High Performance Thin Layer Chromatography) plate showed that the purified pullulanase caused the complete hydrolysis of pullulan to maltotriose.

A novel pullulanase from a fungus Hypocrea jecorina QM9414: production and biochemical characterization.

Pullulanase production from a fungus Hypocrea jecorina QM9414 that produces native extracellular hydrolases having industrial applications was carried out in a shaking flask culture containing 0.5% amylopectin at a pH of 6.50 at 30°C. The enzyme was purified 11-fold by ammonium sulfate fractionation, anion-exchange and gel-filtration chromatographies with a yield of 10.12% and a specific activity of 1.36 ± 0.14 U/mg protein. The molecular mass of pullulanase was estimated to be 130.56 kDa by PAGE and SDS-PAGE, indicating that the native enzyme was a monomer. The optimum pH and temperature for purified enzyme was 6.5 and between 35°-65°C, respectively. The Km values for amylopectin, starch and pullulan as substrates were 10.7, 15.5 and 38.4 mg/mL, respectively. The Vmax values were found to be 3.32, 3.32 and 3.82 ΔA/min for amylopectin, starch and pullulan, respectively. The enzyme was stable at 40-70°C for 30 min, but lost about 33% of its activity at 80°C and about 43% of activity at 90°C and 100°C for the same incubation period. Pullulanase activity was stimulated by CoCl2, NiCl2, KI, NaCl, MgCl2, and LiSO4. The enzyme was slightly inhibited by urea, CaCl2 and b-mercaptoethanol. The enyzmatic characteristics, substrate specificity and the products of hydrolysis indicated that the enzyme was similar to those of type II pullulanases.

Optimization of medium components using response surface methodology for production of thermostable amylopullulanase in submerged fermentation by Clostridium thermosulfurogenes SVM17

Response surface methodology (RSM) based on central composite rotatable design (CCRD) was used to determine the optimal levels of medium components, viz., soluble starch, tapioca flour, peptone, magnesium chloride and ferrous sulphate for enhanced thermostable amylopullulanase production by Clostridium thermosulfurogenes SVM17 in submerged fermentation. The design contains a total of 54 experimental trials with first 32 organized in a fractional factorial design and experimental trials from 33-40 and 51-54 involving the replication of the central points. Within the tested range of concentrations, all medium components were found significant. The optimum levels of nutrients for maximum production of enzyme were (% w/v): potato starch, 5.2; tapioca flour, 6.3; peptone, 2.5; MgCl2·6H2O, 0.015 and FeSO4·7H2O, 6.0 ppm. After optimization of medium components, the strain SVM17 showed 96 and 409 % increased amylase and pullulanase activities, respectively when compared with the non-optimized conditions.

Purification and characterization of highly thermostable amylopullulanase from a thermophilic, anaerobic bacterium Clostridium thermosulfurogenes SVM17

A highly thermostable amylopullulanase was purified to homogeneity from the culture filtrate of the Clostridium thermosulfurogenes SVM17. On SDS-PAGE, the purified fraction having both amylase and pullulanase activities were observed as a single band. The molecular weight of the purified amylopullulanase on SDS-PAGE was 97 kDa. The optimum temperature for both amylase and pullulanase was 70 °C. The enzyme was completely stable at 70 °C for 2 h. The presence of 5% starch increased the thermal stability of the enzyme at 100 °C up to 2 h. Both amylase and pullulanase activities were optimum at pH 5.5 to 6.0 and were stable over a pH range of 4.0 to 6.5. The TLC analysis of the reaction products on starch showed that maltose was the main product along with trace amounts of glucose. The analysis of hydrolysis product of pullulan showed that maltotriose was the main product. At 5 mM concentration, Mn2+ and Ag+ strongly stimulated both amylase and pullulanase activities, where as Mg2+, Ca2+, Cu2+, Fe3+, Zn2+, Hg2+, EDTA, Cd2+ and Li2+ inhibited both amylase and pullulanase activities. When the concentration of metal ions was increased from 5 to10 mM, a further increase in amylase activity was observed in the presence of Ni2+, Mn2+ and Co2+. Where as substantial decrease was observed at 10 mM concentration of Ag+, Pb2+ and Ca2+.