Enhancement of extracellular pullulanase production from recombinant Escherichia coli by combined strategy involving auto-induction and temperature control

Microbial production of hyaluronic acid: The current advances, engineering strategies and trends

Hyaluronic acid (HA) is a versatile biomolecule with applications in medicine, cosmetics, and pharmaceuticals. While traditionally extracted from animal tissues, HA is now predominantly produced through microbial fermentation. Microbial fermentation using strains such as Streptococcus zooepidemicus, Corynebacterium glutamicum, and Bacillus subtilis offers a more scalable and sustainable alternative to chemical and animal extraction methods. Recent studies reveal promising yields from engineered strains of Corynebacterium glutamicum and Bacillus subtilis, utilizing advanced metabolic and genetic techniques. Recent advancements in genetic and metabolic engineering, as well as synthetic biology, have addressed some challenges related to molecular weight, viscosity, and by-product formation. This review focuses on the microbial production of HA using engineered strains, encompassing producer organisms, metabolic engineering strategies, industrial-scale production, and key factors influencing molecular weight. Furthermore, it addresses the challenges and potential solutions associated with HA production. Additional research is necessary to develop more efficient and robust engineered strains that exhibit resistance to contamination and can utilize low-cost substrates, such as Pseudomonas putida and Halomonas spp. By overcoming these challenges, researchers can advance the industrial production of HA and expand its applications, thereby contributing to the growth of the HA market.

An efficient approach for overproduction of DNA polymerase from Pyrococcus furiosus using an optimized autoinduction system in Escherichia coli

High fidelity DNA polymerase from Pyrococcus furiosus (Pfupol) is an attractive alternative to the highly popular DNA polymerase from Thermus aquaticus. Because this enzyme is in great demand for biotechnological applications, optimizing Pfupol production is essential to supplying the industry's expanding demand. T7-induced promoter expression in Escherichia coli expression systems is used to express recombinant Pfupol; however, this method is not cost-effective. Here, we have effectively developed an optimized process for the autoinduction approach of Pfupol expression in a defined medium. To better examine Pfupol's activities, its purified fraction was used. A 71 mg/L of pure Pfupol was effectively produced, resulting in a 2.6-fold increase in protein yield when glucose, glycerol, and lactose were added in a defined medium at concentrations of 0.05%, 1%, and 0.6%, respectively, and the condition for production in a 5 L bioreactor was as follow: 200 rpm, 3 vvm, and 10% inoculant. Furthermore, the protein exhibited 1445 U/mg of specific activity when synthesized in its active state. This work presents a high level of Pfupol production, which makes it an economically viable and practically useful approach.

Biotechnology and bioengineering of pullulanase: state of the art and perspectives

Pullulanase (EC 3.2.1.41) is a starch-debranching enzyme in the α-amylase family and specifically cleaves α-1,6-glycosidic linkages in starch-type polysaccharides, such as pullulan, β-limited dextrin, glycogen, and amylopectin. It plays a key role in debranching and hydrolyzing starch completely, thus bring improved product quality, increased productivity, and reduced production cost in producing resistant starch, sugar syrup, and beer. Plenty of researches have been made with respects to the discovery of either thermophilic or mesophilic pullulanases, however, few examples meet the demand of industrial application. This review presents the progress made in the recent years from the first aspect of characteristics of pullulanases. The heterologous expression of pullulanases in different microbial hosts and the methods used to improve the expression effectiveness and the regulation of enzyme production are also described. Then, the function evolution of pullulanases from a protein engineering view is discussed. In addition, the immobilization strategy using novel materials is introduced to improve the recyclability of pullulanases. At the same time, we indicate the trends in the future research to facilitate the industrial application of pullulanases.

Discovering and efficiently promoting the extracellular secretory expression of Thermobacillus sp. ZCTH02-B1 sucrose phosphorylase in Escherichia coli

Sucrose phosphorylase (SPase, EC2.4.1.7) is a promising transglycosylation biocatalyst used for producing glycosylated compounds that are widely used in the food, cosmetics, and pharmaceutical industries. In this study, a recombinant SPase from the Thermobacillus sp. ZCTH02-B1 (rTSPase), which was previously reported to have high thermostability and the catalytic ability to synthesize ascorbic acid 2-glucoside, was attempted to be extracellularly expressed in Escherichia coli BL21(DE3) by fusion of endogenous osmotically-inducible protein Y. Unexpectedly, the rTSPase itself was produced outside the cells with an underestimated performance, although no typical signal peptide was predicted. Further N- and C-terminal truncation experiments revealed that both termini of rTSPase have an important role in protein folding and enzymatic activity, while its secretion was N-terminus associated. Extracellular protein concentration and rTSPase activity achieved 1.8 mg/mL and 6.2 U/mL after induction of 36 h in a 5-L fermenter. High-level extracellular rTSPase production could also be obtained from E. coli within 24 h by inducing overexpression of D, D-carboxypeptidase for cell lysis.

Enhancement of extracellular bispecific anti-MUC1 nanobody expression in E. coli BL21 (DE3) by optimization of temperature and carbon sources through an autoinduction condition

Escherichia coli is one of the most suitable hosts for production of antibodies and antibody fragments. Antibody fragment secretion to the culture medium improves product purity in cell culture and diminishes downstream costs. In this study, E. coli strain BL21 (DE3) harboring gene encoding bispecific anti-MUC1 nanobody was selected, and the autoinduction methodology for expression of bispecific anti-MUC1 nanobody was investigated. Due to the replacement of IPTG by lactose as inducer, less impurity and toxicity in the final product were observed. To increase both intracellular and extracellular nanobody production, initially, the experiments were performed for the key factors including temperature and duration of protein expression. The highest amount of nanobody was produced after 21 h at 33°C. The effect of different carbon sources, glycerol, glucose, lactose, and glycine as a medium additive at optimum temperature and time were also assessed by using response surface methodology. The optimized concentrations of carbon sources were obtained as 0.75% (w/v), 0.03% (w/v), 0.1% (w/v), and 0.75% (w/v) for glycerol, glucose, lactose, and glycine, respectively. Finally, the production of nanobody in 2 L fermenter under the optimized autoinduction conditions was evaluated. The results show that the total titer of 87.66 µg/mL anti-MUC1 nanobody, which is approximately seven times more than the total titer of nanobody produced in LB culture medium, is 12.23 µg/L .

Heterologous expression and functional study of nitric oxide reductase catalytic reduction peptide from Achromobacter denitrificans strain TB

Biological denitrification is a promising and green technology for air pollution control. To investigate the nitric oxide reductase (NOR) that dominates NO reduction efficiency in biological purification, the heterologous prokaryotic expression system of the norB gene, which encodes the core peptide of the catalytic reduction structure in the NOR from Achromobacter denitrificans strain TB, was constructed in Escherichia coli BL21 (DE3). Results showed that the 1218 bp-long norB gene was expressed at the highest level under 1.0 mM IPTG for 5 h at 30 °C, and the relative expression abundance of norB in recombinant E. coli was increased by 16.6 times compared with that of the wild-type TB. However, the NO reduction efficiency and NOR activity of strain TB was 2.7 and 1.83 times higher than those of recombinant E. coli, respectively. On the basis of genomic reassembly and protein structure modeling, the core peptide of the NOR catalytic reduction structure from Achromobacter sp. TB can independently exert NO reduction. The low NO degradation efficiency of recombinant E. coli may be due to the lack of a NorC-like structure that increases the enzyme activity of the NorB protein. The results of this study can be used as basis for further research on the structure and function of NOR.

Extracellular production of recombinant N-glycosylated anti-VEGFR2 monobody in leaky Escherichia coli strain

OBJECTIVE

To improve the production yield of N-glycosylated anti-VEGFR2 (vascular endothelial growth factor receptor 2) monobody (FN3_VEGFR2-Gly) in lpp knockout Escherichia coli cells harboring Campylobacter jejuni N-glycosylation pathway.

RESULTS

The leaky CLM37-Δlpp strain efficiently secreted FN3_VEGFR2-Gly into culture medium. The extracellular levels of glycosylated FN3_VEGFR2-Gly in CLM37-Δlpp culture medium were approximately 11 and 15 times higher compared to those in CLM37 cells via IPTG and auto-induction, respectively. In addition, the highest level of total glycosylated FN3_VEGFR2-Gly (70 ± 3.4 mg/L) was found in culture medium via auto-induction. Furthermore, glycosylated FN3_VEGFR2-Gly was more stable than unglycosylated FN3_VEGFR2-Gly in this expression system, but their bioactivities were relatively similar.

CONCLUSIONS

Lpp knockout leaky E. coli strain combined with auto-induction method can enhance the extracellular production of homogenous N-glycosylated FN3_VEGFR2-Gly, and facilitate the downstream protein purification. The findings of this study may provide practical implications for the large-scale production and cost-effective harvesting of N-glycosylation proteins.

Improving production of N-glycosylated recombinant proteins by leaky Escherichia coli

Escherichia coli has been considered as a promising host for the production of N-glycosylated therapeutic proteins and glycoconjugate vaccines. In this study, we developed a simple and efficient strategy for improving the production of N-glycosylated recombinant proteins by combining auto-induction with the use of a leaky E. coli strain. A leaky E. coli strain, designated as CLM37-Δlpp, was engineered by deleting the Braun's lipoprotein (lpp) gene of E. coli strain CLM37. Three distinct acceptor model N-glycosylated proteins, glyco-tagged human tenth fibronectin type III domain (FN3-Gly), enhanced green fluorescent protein (eGFP-Gly), and scFv of vascular endothelial growth factor receptor 3 (scFv-_VEGFR3-Gly) were then expressed in CLM37-Δlpp, which carried an N-glycosylation machinery from Campylobacter jejuni for the investigation of glycoprotein production. As much as 75%, 65%, and 60% of the glycosylated FN3-Gly, eGFP-Gly, and scFv-_VEGFR3-Gly, respectively, were found in the culture medium. The yields of glycosylated FN3-Gly, eGFP-Gly, and scFv-_VEGFR3-Gly were 106 ± 7.4 mg/L, 65 ± 2.5 mg/L, and 62 ± 4.3 mg/L, respectively, which were more than three folds the corresponding yields obtained when these proteins were expressed in CLM37, the unmodified strain. The results suggested that this simplified approach could improve the production of N-glycosylated proteins with E. coli to facilitate large-scale production.

Industrially produced pullulanases with thermostability: Discovery, engineering, and heterologous expression

Pullulanases (EC 3.2.1.41) are well-known starch-debranching enzymes widely used to hydrolyze α-1,6-glucosidic linkages in starch, pullulan, amylopectin, and other oligosaccharides, with application potentials in food, brewing, and pharmaceutical industries. Although extensive studies are done to discover and express pullulanases, only few are available with desirable characteristics for industrial applications. This raises the challenge to mine new enzyme sources, engineer proteins based on sequence/structure, and regulate expressions. We review here the identification of extremophilic and mesophilic microbes as sources of industrial pullulanases with desirable characteristics, including acid-resistance, thermostability, and psychrotrophism. We present current advances in site-directed mutagenesis and sequence/structure-guided protein engineering of pullulanases. In addition, we discuss heterologous expression of pullulanases in prokaryotic and eukaryotic microbial systems, and address the effectiveness of the expression elements and their regulation of enzyme production. Finally, we indicate future research needs to develop desired industrial pullulanases.

N-Terminal Domain Truncation and Domain Insertion-Based Engineering of a Novel Thermostable Type I Pullulanase from Geobacillus thermocatenulatus

A novel thermostable type I pullulanase gene ( pul _GT) from Geobacillus thermocatenulatus DSMZ730 was cloned. It has an open reading frame of 2154 bp encoding 718 amino acids. G. thermocatenulatus pullulanase (Pul_GT) was found to be optimally active at pH 6.5 and 70 °C. It exhibited stable activity in the pH range of 5.5-7.0. Pul_GT lacked three domains (CBM41 domain, X25 domain, and X45 domain) compared with the pullulanase from Bacillus acidopullulyticus ( 2WAN ). Different N-terminally domain truncated (730T) or spliced (730T-U1 and 730T-U2) mutants were constructed. Truncating the N-terminal 85 amino acids decreased the K_m value and did not change its optimum pH, an advantageous biochemical property in some applications. Compared with 2WAN , Pul_GT can be used directly for maize starch saccharification without adjusting the pH, which reduces cost and improves efficiency.

A two-stage temperature control strategy enhances extracellular secretion of recombinant α-cyclodextrin glucosyltransferase in Escherichia coli

The effects of temperature on extracellular secretion of the α-cyclodextrin glucosyltransferase (α-CGTase) from Paenibacillus macerans JFB05-01 by Escherichia coli were investigated. When protein expression was induced at constant temperature, the greatest amount of extracellular recombinant α-CGTase was produced at 25 °C. Higher or lower induction temperatures were not conducive to extracellular secretion of recombinant α-CGTase. To enhance extracellular secretion of α-CGTase by E. coli, a two-stage temperature control strategy was adopted. When expression was induced at 25 °C for 32 h, and then the temperature was shifted to 30 °C, the extracellular α-CGTase activity at 90 h was 45% higher than that observed when induction was performed at a constant temperature of 25 °C. Further experiments suggested that raising the induction temperature can benefit the transport of recombinant enzyme and compensate for the decreased rate of recombinant enzyme synthesis during the later stage of expression. This report provides a new method of optimizing the secretory expression of recombinant enzymes by E. coli.

Efficient extracellular expression of Bacillus deramificans pullulanase in Brevibacillus choshinensis

In this study, the pullulanase gene from Bacillus deramificans was efficiently expressed in Brevibacillus choshinensis. The optimal medium for protein expression was determined through a combination of single-factor experiments and response surface methodology. The initial pH of the medium and the culture temperature were optimized. The pullulanase yield increased 10.8-fold through medium and condition optimization at the shake-flask level. From the results of these experiments, the dissolved oxygen level was optimized in a 3-L fermentor. Under these optimized conditions, the pullulanase activity and the specific pullulanase productivity reached 1005.8 U/mL and 110.5 × 103 U/g dry cell weight, respectively, with negligible intracellular expression. The Brevibacillus choshinensis expression system has proven to be valuable for the extracellular production of pullulanase.

Downsizing a pullulanase to a small molecule with improved soluble expression and secretion efficiency in Escherichia coli

Background

Significant challenges, including low expression and extracellular secretion of soluble protein, are encountered in expressing and purifying Bacillus acidopullulyticus pullulanase (BaPul) in Escherichia coli.

Methods

An N-terminal domain truncation was adopted to facilitate BaPul variant expression and/or secretion.

Results

BaPul possesses a complex modular architecture that consists of CBM41-X45a-X25-X45b-CBM48-GH13. The activities of M1 (ΔCBM41) and M5 (ΔCBM41ΔX25) variants were 2.9- and 2.4-fold that of wild-type (WT) enzyme, respectively. The enhanced expression of soluble protein is the main reason for these improved activities. PelB-M1 and PelB-M5 were transported to the periplasmic space, where PelB is part of the PelB-pET28a(+) construct, and PelB-M3 (ΔX25) and PelB-WT variants were largely retained in the cytoplasm. After fermentation, about 56.6 and 93.4 % of the total activity of PelB-M1 and PelB-M5 were transferred to the periplasm, respectively, followed by cell lysis and leakage of the partial enzyme into the extracellular medium. The optimal temperature and pH for purified preparations of M1, M3, and M5 were similar to those of the WT enzyme. In a starch saccharification reaction, the dextrose equivalents of M1, M3, and M5 proteins were 94.7, 94.5, and 93.1 %, respectively, which were also essentially identical to that of WT (93.6 %).

Conclusion

The deletion of CBM41 and/or X25 domain did not affect the enzyme application, and the truncated variants were more highly expressed and secreted in E. coli. Thus, the truncated variants may be more suitable for industrial applications.

Extracellular expression of natural cytosolic arginine deiminase from Pseudomonas putida and its application in the production of L-citrulline

The Pseudomonas putida arginine deiminase (ADI), a natural cytosolic enzyme, and Thermobifida fusca cutinase were co-expressed in Escherichia coli, and the optimized cutinase gene was used for increasing its expression level. 90.9% of the total ADI protein was released into culture medium probably through a nonspecific leaking mechanism caused by the co-expressed cutinase. The enzymatic properties of the extracellular ADI were found to be similar to those of ADI prepared by conventional cytosolic expression. Extracellular production of ADI was further scaled up in a 3-L fermentor. When the protein expression was induced by IPTG (25.0μM) and lactose (0.1gL(-1)h(-1)) at 30°C, the extracellular ADI activity reached 101.2UmL(-1), which represented the highest ADI production ever reported. In addition, the enzymatic synthesis of l-citrulline was performed using the extracellularly expressed ADI, and the conversion rate reached 100% with high substrate concentration at 650gL(-1).

Triton X-100 enhances the solubility and secretion ratio of aggregation-prone pullulanase produced in Escherichia coli

The pullulanase from Bacillus deramificans is an industrially useful starch-debranching enzyme that is difficult to produce in large quantities. In this study, B. deramificans pullulanase was found to be an aggregation-prone protein that can be solubilized from the insoluble fraction by surfactants in vitro. Studying the effects of various surfactants on pullulanase production in Escherichia coli in shake flasks revealed that optimal pullulanase production could be obtained by adding 0.5% Triton X-100 during the later period of fermentation. A modified fed-batch fermentation strategy was then applied to the production of pullulanase in a 3-L fermentor. When supplemented with 0.5% Triton X-100 at 40 h, the maximal extracellular pullulanase production and secretion ratio were 812.4 U mL(-1) and 86.0%, which were 46.2- and 47.8-fold that of the control, respectively.

Enhancing the secretion efficiency and thermostability of a Bacillus deramificans pullulanase mutant (D437H/D503Y) by N-terminal domain truncation

Pullulanase (EC 3.2.1.41), an important enzyme in the production of starch syrup, catalyzes the hydrolysis of α-1,6 glycosidic bonds in complex carbohydrates. A double mutant (DM; D437H/D503Y) form of Bacillus deramificans pullulanase was recently constructed to enhance the thermostability and catalytic efficiency of the enzyme (X. Duan, J. Chen, and J. Wu, Appl Environ Microbiol 79:4072-4077, 2013, http://dx.doi.org/10.1128/AEM.00457-13). In the present study, three N-terminally truncated variants of this DM that lack the CBM41 domain (DM-T1), the CBM41 and X25 domains (DM-T2), or the CBM41, X25, and X45 domains (DM-T3) were constructed. Upon expression, DM-T3 existed as inclusion bodies, while 72.8 and 74.8% of the total pullulanase activities of DM-T1 and DM-T2, respectively, were secreted into the medium. These activities are 2.8- and 2.9-fold that of the DM enzyme, respectively. The specific activities of DM-T1 and DM-T2 were 380.0 × 10(8) and 449.3 × 10(8) U · mol(-1), respectively, which are 0.94- and 1.11-fold that of the DM enzyme. DM-T1 and DM-T2 retained 50% of their activity after incubation at 60°C for 203 and 160 h, respectively, which are 1.7- and 1.3-fold that of the DM enzyme. Kinetic studies showed that the Km values of DM-T1 and DM-T2 were 1.5- and 2.7-fold higher and the Kcat/Km values were 11 and 50% lower, respectively, than those of the DM enzyme. Furthermore, DM-T1 and DM-T2 produced d-glucose contents of 95.0 and 94.1%, respectively, in a starch saccharification reaction, which are essentially identical to that produced by the DM enzyme (95%). The enhanced secretion and improved thermostability of the truncation mutant enzymes make them more suitable than the DM enzyme for industrial processes.

Enhanced extracellular production of recombinant Bacillus deramificans pullulanase in Escherichia coli through induction mode optimization and a glycine feeding strategy

Process optimization strategies were developed to improve extracellular production of recombinant Bacillus deramificans pullulanase in Escherichia coli. Cell growth and pullulanase production in shake-flask cultures were investigated as a function of the concentration of added glycine, and the type and concentration of inducer. From the results of these experiments, a fed-batch fermentation strategy for high-cell-density cultivation was applied in a 3-L fermentor. The gradual addition of lactose was utilized for the induction of protein expression. The optimal lactose feeding rate and induction point were 0.4gL(-1)h(-1) and a dry cell weight (DCW) of 15gL(-1), respectively. Furthermore, a glycine feeding strategy was formulated to promote the secretion of recombinant protein. The optimal total and extracellular pullulanase activity were 2523.5 and 1567.9UmL(-1), respectively, which represent 1.2 and 22.6-fold increases compared with those observed under unoptimized conditions.