Simple amino acid tags improve both expression and secretion ofCandida antarcticalipase B in recombinantEscherichia coli

Efficient production of a highly active lysozyme from European flat oyster Ostrea edulis

Lysozyme, an antimicrobial agent, is extensively employed in the food and healthcare sectors to facilitate the breakdown of peptidoglycan. However, the methods to improve its catalytic activity and secretory expression still need to be studied. In the present study, twelve lysozymes from different origins were heterologously expressed using the Komagataella phaffii expression system. Among them, the lysozyme from the European flat oyster Ostrea edulis (oeLYZ) showed the highest activity. Via a semi-rational approach to reduce the structural free energy, the double mutant Y15A/S39R (oeLYZdm) with the catalytic activity 1.8-fold greater than that of the wild type was generated. Subsequently, different N-terminal fusion tags were employed to enhance oeLYZdm expression. The fusion with peptide tag 6×Glu resulted in a remarkable increase in the recombinant oeLYZdm expression, from 2.81 × 103 U mL-1 to 2.11 × 104 U mL-1 in shake flask culture, and eventually reaching 2.05 × 105 U mL-1 in a 3-L fermenter. The work produced the greatest amount of heterologous oeLYZ expression in microbial systems that are known to exist. Reducing the structural free energy and employing the N-terminal fusion tags are effective strategies to improve the catalytic activity and secretory expression of lysozyme.

A New Approach in Lipase-Octyl-Agarose Biocatalysis of 2-Arylpropionic Acid Derivatives

The use of lipase immobilized on an octyl-agarose support to obtain the optically pure enantiomers of chiral drugs in reactions carried out in organic solvents is a great challenge for chemical and pharmaceutical sciences. Therefore, it is extremely important to develop optimal procedures to achieve a high enantioselectivity of the biocatalysts in the organic medium. Our paper describes a new approach to biocatalysis performed in an organic solvent with the use of CALB-octyl-agarose support including the application of a polypropylene reactor, an appropriate buffer for immobilization (Tris base-pH 9, 100 mM), a drying step, and then the storage of immobilized lipases in a climatic chamber or a refrigerator. An immobilized lipase B from Candida antarctica (CALB) was used in the kinetic resolution of (R,S)-flurbiprofen by enantioselective esterification with methanol, reaching a high enantiomeric excess (eep = 89.6 ± 2.0%). As part of the immobilization optimization, the influence of different buffers was investigated. The effect of the reactor material and the reaction medium on the lipase activity was also studied. Moreover, the stability of the immobilized lipases: lipase from Candida rugosa (CRL) and CALB during storage in various temperature and humidity conditions (climatic chamber and refrigerator) was tested. The application of the immobilized CALB in a polypropylene reactor allowed for receiving over 9-fold higher conversion values compared to the results achieved when conducting the reaction in a glass reactor, as well as approximately 30-fold higher conversion values in comparison with free lipase. The good stability of the CALB-octyl-agarose support was demonstrated. After 7 days of storage in a climatic chamber or refrigerator (with protection from humidity) approximately 60% higher conversion values were obtained compared to the results observed for the immobilized form that had not been stored. The new approach involving the application of the CALB-octyl-agarose support for reactions performed in organic solvents indicates a significant role of the polymer reactor material being used in achieving high catalytic activity.

Efficient production and characterization of a newly identified trehalase for inhibiting the formation of bacterial biofilms

Trehalase has attracted widespread attention in medicine, agriculture, food, and ethanol industry due to its ability to specifically degrade trehalose. Efficient expression of trehalase remains a challenge. In this study, a putative trehalase-encoding gene (Tre-zm) from Zunongwangia mangrovi was explored using gene-mining strategy and heterologously expressed in E. coli. Trehalase activity reached 3374 U·mL-1 after fermentation optimization. The scale-up fermentation in a 15 L fermenter was achieved with a trehalase production of 15,068 U·mL-1. The recombinant trehalase TreZM was purified and characterized. It displayed optimal activity at 35 °C and pH 8.5, with Mn2+, Sn2+, Na+, and Fe2+ promoting the activity. Notably, TreZM showed significant inhibition effect on biofilm forming of Staphylococcus epidermidis. The combination of TreZM with a low concentration of antibiotics could inhibit 70 % biofilm formation of Staphylococcus epidermidis and 28 % of Pseudomonas aeruginosa. Hence, this study provides a promising candidate for industrial production of trehalase and highlights its potential application to control harmful biofilms.

Efficient secretion of an enzyme cocktail in Escherichia coli for hemicellulose degradation

The use of host to secrete several hemicellulase is a cost-effective way for hemicellulose degradation. In this study, the xylose utilization gene xylAB of Escherichia coli BL21 was knocked out, and the xylanase (N20Xyl), β-xylosidase (Xys), and feruloyl esterase (FaeLam) were co-expressed in this strain. By measuring the content of reducing sugars generated by enzymatic hydrolysis of wheat bran in the fermentation supernatant, the order of the three enzymes was screened to obtain the optimal recombinant strain of E. coli BL21/∆xylAB/pDIII-2. Subsequently, fermentation conditions including culture medium, inducer concentration, induction timing, metal ions, and glycine concentration were optimized. Then, different concentrations of wheat bran and xylan were added to the fermentation medium for degradation. The results showed that the extracellular reducing sugars content reached the highest value of 33.70 ± 0.46 g/L when 50 g/L xylan was added. Besides, the scavenging rates of hydroxyl radical by the fermentation supernatant was 81.0 ± 1.41 %, and the total antioxidant capacity reached 2.289 ± 0.55. Furthermore, it showed the growth promotion effect on different lactic acid bacteria. These results provided a basis for constructing E. coli strain to efficiently degrade hemicellulose, and the strain obtained has great potential application to transform hemicellulose into fermentable carbon source.

Enhanced expression of a novel trypsin from Streptomyces fradiae in Komagataella phaffii GS115 through combinational strategies of propeptide engineering and self-degredation sites modification

This study aimed to enhance the expression level of a novel trypsin gene from Streptomyces fradiae ATCC14544 in Komagataella phaffii GS115 through the combinational use of propeptide engineering and self-degradation residues modification strategies. An artificial propeptide consisted of thioredoxin TrxA, the bovine propeptide DDDDK and the hydrophobic peptide FVEF was introduced to replace the original propeptide while the self-degradation residue sites were predicted and analyzed through alanine screening. The results showed that the quantity and enzymatic activity of asft with engineered propeptide reached 47.02 mg/mL and 33.9 U/mL, which were 9.6 % and 59.29 % higher than those of wild-type (42.9 mg/mL and 13.8 U/mL). Moreover, the introduction of R295A/R315A mutation further enhanced the enzymatic activity (58.86 U/mL) and obviously alleviated the phenomena of self-degradation. The tolerance of trypsin towards alkaline environment was also improved since the optimal pH was shifted from pH 9.0 to pH 9.5 and the half-life value at pH 10 was significantly extended. Finally, the fermentation media composition and condition were optimized and trypsin activity in optimal condition reached 160.58 U/mL, which was 2.73-fold and 11.64-fold of that before optimization or before engineering. The results obtained in this study indicated that the combinational use of propeptide engineering and self-degradation sites modification might have great potential application in production of active trypsins.

Specific N-terminal amino acids potentiate the periplasmic expression of single-chain variable fragments in Escherichia coli

Single-chain variable fragments (ScFvs) are important in therapy, diagnosis and research because of their elevated antigen affinity and low immunogenicity. At present, high-yield scFv expression in Escherichia coli is limited by insoluble aggregation in the reducing environment of the cytoplasm or low yields in the periplasm. Here we achieved increased expression of scFvs in the periplasm by inserting optimal amino acids between the signal peptide and scFv. We constructed an expression library with three random amino acids at the scFv N-terminus, screened this library with a single-step colony assay and identified the specific sequences that boosted periplasmic expression of scFvs.

Active Expression of Human Hyaluronidase PH20 and Characterization of Its Hydrolysis Pattern

Hyaluronidases are a group of glycosidases catalyzing the degradation of hyaluronic acid (HA). Because of the advantages of effectively hydrolyzing the HA-rich matrix and low immunogenicity, human hyaluronidase PH20 (hPH20) is widely used in the medical field. Here, we realized the active expression of recombinant hPH20 by Pichia pastoris under a methanol-induced promoter PAOX1. By optimizing the composition of the C-terminal domain and fusing protein tags, we constructed a fusion mutant AP2-△491C with the extracellular hyaluronidase activity of 258.1 U·L-1 in a 3-L bioreactor, the highest expression level of recombinant hPH20 produced by microbes. Furthermore, we found recombinant hPH20 hydrolyzed the β-1,4 glycosidic bonds sequentially from the reducing end of o-HAs, with HA6 NA as the smallest substrate. The result will provide important theoretical guidance for the directed evolution of the enzyme to prepare multifunctional o-HAs with specific molecular weights.

Continuous Production of Human Epidermal Growth Factor Using Escherichia coli Biofilm

Increasing demand for recombinant proteins necessitates efficient protein production processes. In this study, a continuous process for human epidermal growth factor (hEGF) secretion by Escherichia coli was developed by taking advantage of biofilm formation. Genes bcsB, fimH, and csgAcsgB that have proved to facilitate biofilm formation and some genes moaE, yceA, ychJ, and gshB potentially involved in biofilm formation were examined for their effects on hEGF secretion as well as biofilm formation. Finally, biofilm-based fermentation processes were established, which demonstrated the feasibility of continuous production of hEGF with improved efficiency. The best result was obtained from ychJ-disruption that showed a 28% increase in hEGF secretion over the BL21(DE3) wild strain, from 24 to 32 mg/L. Overexpression of bcsB also showed great potential in continuous immobilized fermentation. Overall, the biofilm engineering here represents an effective strategy to improve hEGF production and can be adapted to produce more recombinant proteins in future.

Functional expression and extracellular secretion of Clostridium thermocellum Cel48S cellulase in Escherichia coli via the signal recognition particle-dependent translocation pathway

As the only glycoside hydrolase family 48 member in Clostridium thermocellum, the exoglucanase Cel48S plays a crucial role in the extremely high activity of the cellulosome against crystalline cellulose. Although the importance of Cel48S in the hydrolysis of crystalline cellulose has been widely accepted, an efficient production system has not yet been established because Cel48S is usually expressed in Escherichia coli within inactive inclusion bodies. For unstable proteins like Cel48S, translocation across the inner membrane can be more advantageous than cytoplasmic production due to the presence of folding modulators in the periplasm and the absence of cytoplasmic proteases. In this study, we evaluated whether the production of Cel48S in the periplasmic space of E. coli could enhance its functional expression. To do so, we attached the PelB signal peptide, which mediates post-translational secretion, to the N-terminal end of Cel48S (P-Cel48S). The PelB signal peptide allowed catalytically active Cel48S to be successfully produced in the culture medium. In addition, we investigated the role of an alternative co-translational pathway on the extracellular production of Cel48S, finding that co-translational secretion yielded a specific activity of recombinant Cel48S of 135.1 ± 10.0 U/mg cell in the culture medium, which was 2.2 times higher than that associated with P-Cel48S expression. Therefore, we believe that our approach has potential applications for the cost-effective conversion of lignocellulosic biomass and the industrial production of other unstable proteins.

Heat-induced overexpression of the thermophilic lipase from Bacillus thermocatenulatus in Escherichia coli by fermentation and its application in preparation biodiesel using rapeseed oil

Due to its simple, less by-product and environment friendly properties, enzymatic transesterification of oil with short-chain alcohol to biodiesel, fatty acid methyl esters (FAMEs) is considered to be a promising way of green production and has attracted much attention. In this study, FAMEs were synthesized by an enzymatic method with recombinant lipase as catalysts. A thermophilic Bacillus thermocatenulatus lipase 2 (BTL2) was overexpressed in Escherichia coli BL21(DE3) through relative and quantitative analysis using real-time quantitative PCR. The results suggested that the BTL2 gene was overexpressed in E. coli at the mRNA level, and the recombinant strain harboring a high-copy number vectors was selected and applied to fermentation to produce BTL2 with enzyme activity of 35.54 U/mg cells. The recombinant BTL2 solution exhibited excellent resistance to neutral pH, high temperature, and organic solvents after a certain treatment. Finally, the effects of enzymatic transesterification for preparing biodiesel were studied, using rapeseed oil as raw material, as well as BTL2 solution as catalysts, which resulted in 86.04% yield of FAMEs under 50°C for 36 h. The liquid BTL2 was directly used to prepare FAMEs at a higher temperature efficiently, making the thermophilic BTL2 had the potential application value in biodiesel reproduction subsequently.

Perturbation of the peptidoglycan network and utilization of the signal recognition particle-dependent pathway enhances the extracellular production of a truncational mutant of CelA in Escherichia coli

Caldicellulosiruptor bescii is the most thermophilic, cellulolytic bacterium known and has the native ability to utilize unpretreated plant biomass. Cellulase A (CelA) is the most abundant enzyme in the exoproteome of C. bescii and is primarily responsible for its cellulolytic ability. CelA contains a family 9 glycoside hydrolase and a family 48 glycoside hydrolase connected by linker regions and three carbohydrate-binding domains. A truncated version of the enzyme (TM1) containing only the endoglucanase domain is thermostable and actively degrades crystalline cellulose. A catalytically active TM1 was successfully produced via the attachment of the PelB signal peptide (P-TM1), which mediates post-translational secretion via the SecB-dependent translocation pathway. We sought to enhance the extracellular secretion of TM1 using an alternative pathway, the signal recognition particle (SRP)-dependent translocation pathway. The co-translational extracellular secretion of TM1 via the SRP pathway (D-TM1) resulted in a specific activity that was 4.9 times higher than that associated with P-TM1 overexpression. In batch fermentations, the recombinant Escherichia coli overexpressing D-TM1 produced 1.86 ± 0.06 U/ml of TM1 in the culture medium, showing a specific activity of 1.25 ± 0.05 U/mg cell, 2.7- and 3.7-fold higher than the corresponding values of the strain overexpressing P-TM1. We suggest that the TM1 secretion system developed in this study can be applied to enhance the capacity of E. coli as a microbial cell factory for the extracellular secretion of this as well as a variety proteins important for commercial production.

Enhancing acid tolerance of Escherichia coli via viroporin-mediated export of protons and its application for efficient whole-cell biotransformation

Escherichia coli-based whole-cell biocatalysts are widely used for the sustainable production of value-added chemicals. However, weak acids present as substrates and/or products obstruct the growth and fermentation capability of E. coli. Here, we show that a viroporin consisting of the influenza A matrix-2 (M2) protein, is activated by low pH and has proton channel activity in E. coli. The heterologous expression of the M2 protein in E. coli resulted in a significant increase in the intracellular pH and cell viability in the presence of various weak acids with different lengths of carbon chains. In addition, the feasibility of developing a robust and efficient E. coli-based whole-cell biocatalyst via introduction of the proton-selective viroporin was explored by employing (Z)-11-(heptanolyoxy)undec-9-enoic acid (ester) and 2-fucosyllactose (2'-FL) as model products, whose production is hampered by cytosolic acidification. The engineered E. coli strains containing the proton-selective viroporin exhibited approximately 80% and 230% higher concentrations of the ester and 2'-FL, respectively, than the control strains without the M2 protein. The simple and powerful strategy developed in this study can be applied to produce other valuable chemicals whose production involves substrates and/or products that cause cytosolic acidification.

Expression of porcine interferon-α and its bioactivity analysis in vitro and in vivo

Interferon α (IFN-α) plays a crucial role in the host's immune response. In this study, the amino acid sequence of porcine interferon α (PoIFN-α) was analyzed. Seven substitutions, S38F, H40Q, F43L, N78D, Y86C, S151A, and R156T, were mutated and obtained by aligning the sequences of PoIFN-α subtypes. The PoIFN-α mutants were designed, expressed, and purified in E. coli. The antiviral activities of these PoIFN-αs were measured in Vero and swine testis cells against vesicular stomatitis virus (VSV). Their inhibitory abilities on pseudorabies virus (PRV) were also examined. Commercial PoIFN-α was used as a control. We found the ideal inducer concentration of isopropyl β-D-thiogalactoside was 1 mM, and the best time-point for induction was 8 h. The PoIFN-α mutant named PoIFN-α-156s had the highest antiviral activity, which was about 200-fold more than that of PoIFN-α. PoIFN-α-156s could inhibit VSV and PRV replication in a dose-dependent manner in vitro. The half-life of PoIFN-α-156s was longer than that of PoIFN-α in mice, and the effective antiviral action was higher than PoIFN-α. Animal experiments showed that PoIFN-α-156s could decrease the viral load after infection with VSV. Overall, these results suggest that recombinant PoIFN-α-156s has the ability of antivirus, and is feasible for veterinary clinical applications and fundamental research.

Engineering of a Microbial Cell Factory for the Extracellular Production of Catalytically Active Phospholipase A2 of Streptomyces violaceoruber

Phospholipase A2 (PLA2) from Streptomyces violaceoruber is a lipolytic enzyme used in a wide range of industrial applications including production of lysolecithins and enzymatic degumming of edible oils. We have therefore investigated expression and secretion of PLA2 in two workhorse microbes, Pichia pastoris and Escherichia coli. The PLA2 was produced to an activity of 0.517 ± 0.012 U/ml in the culture broth of the recombinant P. pastoris. On the other hand, recombinant E. coli BL21 star (DE3), overexpressing the authentic PLA2 (P-PLA2), showed activity of 17.0 ± 1.3 U/ml in the intracellular fraction and 21.7 ± 0.7 U/ml in the culture broth. The extracellular PLA2 activity obtained with the recombinant E. coli system was 3.2-fold higher than the corresponding value reached in a previous study, which employed recombinant E. coli BL21 (DE3) overexpressing codon-optimized PLA2. Finally, we observed that the extracellular PLA2 from the recombinant E. coli P-PLA2 culture was able to hydrolyze 31.1 g/l of crude soybean lecithin, an industrial substrate, to a conversion yield of approximately 95%. The newly developed E. coli-based PLA2 expression system led to extracellular production of PLA2 to a productivity of 678 U/l·h, corresponding to 157-fold higher than that obtained with the P. pastoris-based system. This study will contribute to the extracellular production of a catalytically active PLA2.

Quarter of a Century after: A Glimpse at the Conformation and Mechanism of Candida antarctica Lipase B

Lipase B from Candida antarctica (CAL-B) belongs to the family of α/β-hydrolases, and is one from the most extensively used biocatalysts in the kinetic resolution of amines and alcohols in a racemic state, in the desymmetrization of diacetates or diols, and in the stereoselective synthesis of chiral intermediate compounds for obtaining the various pharmaceuticals and agents which protect plants. There are also many cases of promiscuous reactions catalyzed by CAL-B. The number of very important results appeared recently in the literature in the years 2015–2019, regarding the crystal structure and conformation of CAL-B molecule. Before 2015, there was a long period of a complete lack of information concerning this enzyme’s structure. The earlier reports about CAL-B structure were dated between 1994–1995, and did not provide enough conclusions about the mechanism of the enzyme. The recently solved structures give a hint of the enzyme mechanism in three dimensions.

Directly covalent immobilization of Candida antarctica lipase B on oxidized aspen powder by introducing poly‑lysines: An economical approach to improve enzyme performance

In our previous study, we could achieve high soluble expression of Candida antarctica lipase B (CalB) in E. coli by fusion poly‑amino acid tags on CalB (pCalB). Herein, we are surprised to find that pCalB can be easily and directly covalent binding on a simply oxidized aspen powder (OAP) by the aid of poly‑lysine tags. Under the optimal conditions, 72.9 ± 3.6% of the total protein could be immobilized, and the activity recovery of immobilized pCalB (pCalB-OAP) was 98.9 ± 3.8%. The analysis of scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) indicated that OAP was a suitable carrier for enzyme immobilization. The immobilized pCalB-OAP could exhibit excellent thermal stabilities, and it retained a residual activity of 58.4 ± 2.8% at 55 °C, whereas only 21.2 ± 2.2% of its initial activity for free pCalB was observed. And it could also display a nice tolerance for the changes of pH environment, compared with that of free pCalB. The results that pCalB-OAP could retained 73.6 ± 2.9% of their initial activity in (R, S)-NEMPAME hydrolysis after the tenth cycles, suggested that pCalB-OAP could be effectively recycled. The immobilization strategies established here were simple and inexpensive.

Polyionic Tags as Enhancers of Protein Solubility in Recombinant Protein Expression

Since the introduction of recombinant protein expression in the second half of the 1970s, the growth of the biopharmaceutical field has been rapid and protein therapeutics has come to the foreground. Biophysical and structural characterisation of recombinant proteins is the essential prerequisite for their successful development and commercialisation as therapeutics. Despite the challenges, including low protein solubility and inclusion body formation, prokaryotic host systems and particularly Escherichia coli, remain the system of choice for the initial attempt of production of previously unexpressed proteins. Several different approaches have been adopted, including optimisation of growth conditions, expression in the periplasmic space of the bacterial host or co-expression of molecular chaperones, to assist correct protein folding. A very commonly employed approach is also the use of protein fusion tags that enhance protein solubility. Here, a range of experimentally tested peptide tags, which present specific advantages compared to protein fusion tags and the concluding remarks of these experiments are reviewed. Finally, a concept to design solubility-enhancing peptide tags based on a protein’s pI is suggested.

Secretion of recombinant proteins from E. coli

The microorganism Escherichia coli is commonly used for recombinant protein production. Despite several advantageous characteristics like fast growth and high protein yields, its inability to easily secrete recombinant proteins into the extracellular medium remains a drawback for industrial production processes. To overcome this limitation, a multitude of approaches to enhance the extracellular yield and the secretion efficiency of recombinant proteins have been developed in recent years. Here, a comprehensive overview of secretion mechanisms for recombinant proteins from E. coli is given and divided into three main sections. First, the structure of the E. coli cell envelope and the known natural secretion systems are described. Second, the use and optimization of different one- or two-step secretion systems for recombinant protein production, as well as further permeabilization methods are discussed. Finally, the often-overlooked role of cell lysis in secretion studies and its analysis are addressed. So far, effective approaches for increasing the extracellular protein concentration to more than 10 g/L and almost 100% secretion efficiency exist, however, the large range of optimization methods and their combinations suggests that the potential for secretory protein production from E. coli has not yet been fully realized.

High-yield secretory production of stable, active trypsin through engineering of the N-terminal peptide and self-degradation sites in Pichia pastoris

Streptomyces griseus trypsin (SGT) possesses enzymatic properties similar to mammalian trypsins and has great potential applications in the leather processing, bioethanol, detergent and pharmaceutical industry. Here, a new strategy was reported for improving its stable, active secretory production through engineering of its propeptide and self-degradation sites. By rationally introducing hydrophobic mutations into the N-terminus of SGT Exmt (R145I), replacing the propeptide with FPVDDDDK and engineering the α-factor signal peptide, trypsin production (amidase activity) was improved to 177.85±2.83U·mL^-1 in a 3-L fermenter (a 3.75-fold increase). Subsequently, all of the residues involved in autolysis that were identified by mass spectrometry were mutated and the resulting proteins were evaluated. In particular, the variant tbcf (K101A) demonstrated high stability and production (227.65±6.51U·mL^-1 and 185.71±5.68mg·L^-1, respectively). The recombinant strain constructed here has great potential for large-scale production of active trypsin.

Streamlined Preparation of Immobilized Candida antarctica Lipase B

Candida antarctica lipase B (CalB) was efficiently expressed (6.2 g L^-1) in Escherichia coli by utilizing an N-terminal tag cassette and the XylS/Pm expression system in a fed-batch bioreactor; subsequent direct binding to EziG from crude extracts resulted in an immobilized catalyst with superior activity to Novozym 435.

Self-Assembly Nanostructures of Triglyceride-Water Interfaces Determine Functional Conformations of Candida antarctica Lipase B

Candida antarctica lipase B (CalB) acts as a lipase when adsorbed to an acylglyceride interface and as an esterase when exposed to an aqueous environment. The effect of the molecular self-assembly nanostructure of triglyceride-water interfaces on structural conformations of adsorbed CalB and the implications to its catalytic function were studied by molecular dynamics simulations. Systems of CalB adsorbed to interfaces and solvated in water were compared. The two environments induced relative motions of helices α5 and α10 that resulted in open and closed conformations. The open conformation was stabilized by interactions between the polar and nonpolar amino acids of α5 and α10 and the nanostructure of triglyceride aggregates, which self-assembled into crystalline-like patterns of alternating polar and nonpolar lamellae. Thus, the structure of CalB has been adapted by evolution to the geometric constraints imposed by the interface nanostructure for optimized catalytic activity. Helices α5 and α10 have two functions. As mobile elements, they ensure access of bulky substrates to the active site in the open conformation. As a part of the active site pocket, they ensure binding of substrate molecules in a productive orientation near the active site. In water, access to the binding site is limited, and the smaller substrate binding site is beneficial for the binding of small, water-soluble substrates. The CalB crystal structure commonly used for protein engineering studies represents an intermediate state between open and closed, and may thus not be adequate to assess the function of CalB, neither as lipase nor as esterase.

Efficient Secretory Overexpression of Endoinulinase in Escherichia coli and the Production of Inulooligosaccharides

Endoinulinase production was achieved by heteroexpression of endoinulinase-encoding gene from Aspergillus ficuum which is an eukaryotic organism in Escherichia coli BL21 (DE3). Further analysis demonstrated that the native signal peptide existed in inu2 gene lowered the enzyme expression level. To realize extracellular accumulation of target protein and improve its expression level, native signal peptide was substituted with pelB, ompC, and pelB fusing with the native signal peptides; then, the effects on endoinulinase production were investigated. As a result, E. coli A606-3, with replacement of pelB as its signal peptide, showed the highest endoinulinase enzyme activity (75.22 U/mg). Also, it suggested that eukaryotic signal peptides have an inhibition on enzyme expression in prokaryotic organism. Moreover, the condition for inulooligosaccharide (IOS) production from inulin was optimized, and an IOS yield of 94.41 % was achieved under the condition of 15 % (w/v) inulin, purified endoinulinase dosage of 5 U/g inulin, 55 °C, and pH 4.6 for 24 h. The major products of hydrolysis of inulin were identified as DP3 to DP7.

Improved Production of Active Streptomyces griseus Trypsin with a Novel Auto-Catalyzed Strategy

N-terminal sequences play crucial roles in regulating expression, translation, activation and enzymatic properties of proteins. To reduce cell toxicity of intracellular trypsin and increase secretory expression, we developed a novel auto-catalyzed strategy to produce recombinant trypsin by engineering the N-terminus of mature Streptomyces griseus trypsin (SGT). The engineered N-terminal peptide of SGT was composed of the thioredoxin, glycine-serine linker, His₆-tag and the partial bovine trypsinogen pro-peptide (DDDDK). Furthermore, we constructed a variant TLEI with insertion of the artificial peptide at N-terminus and site-directed mutagenesis of the autolysis residue R145. In fed-batch fermentation, the production of extracellular trypsin activity was significantly improved to 47.4 ± 1.2 U·ml⁻¹ (amidase activity, 8532 ± 142.2 U·ml⁻¹ BAEE activity) with a productivity of 0.49 U·ml⁻¹·h⁻¹, which was 329% greater than that of parent strain Pichia pastoris GS115-SGT. This work has significant potential to be scaled-up for microbial production of SGT. In addition, the N-terminal peptide engineering strategy can be extended to improve heterologous expression of other toxic enzymes.

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.

Fatty acid hydration activity of a recombinant Escherichia coli-based biocatalyst is improved through targeting the oleate hydratase into the periplasm

Whole-cell biotransformation of fatty acids can be influenced by the activities of catalytic enzymes and by the efficiency of substrate transport into host cells. Here, we improved fatty acid hydration activity of the recombinant Escherichia coli expressing an oleate hydratase of Stenotrophomonas maltophilia by targeting the catalytic enzyme into the periplasm instead of the cytoplasm. Recombinant E. coli producing OhyA in the periplasm under guidance of the PelB signal sequence (E. coli OhyA_PP) exhibited significantly greater hydration activity with oleic acid and linoleic acid compared to a recombinant E. coli producing OhyA in the cytoplasm (E. coli OhyA_CS). For example, the oleate double bond hydration rate of E. coli OhyA_PP was >400 μmol/g dry cells/min (400 U/g dry cells), which is >10-fold higher than that of E. coli OhyA_CS. As the specific activities of the enzymes targeted into the cytoplasm and periplasm were comparable, we assumed that targeting OhyA into the periplasm could accelerate fatty acid transport to the catalytic enzymes by skipping the major mass transport barrier of the cytoplasmic membrane. Our results will contribute to the development of whole-cell biocatalysts for fatty acid biotransformation.

Extracellular production of Pseudozyma (Candida) antarctica lipase B with genuine primary sequence in recombinant Escherichia coli

An Escherichia coli expression system was established to produce recombinant extracellular Pseudozyma (Candida) antarctica lipase B (CALB). With the aim of producing the genuine CALB without additional amino acid residues, the mature portion of the CALB gene was fused seamlessly to a pelB signal sequence and expressed in E. coli BL21(DE3) using the pET system. Inducing gene expression at low temperature (20°C) was crucial for the production of active CALB; higher temperatures caused inclusion body formation. Prolonged induction for 48 h at 20°C allowed for the enzyme to be released into the culture medium, with more than half of the activity detected in the culture supernatant. A catalytically inactive CALB mutant (S105A) protein was similarly released, suggesting that the lipid-hydrolyzing activity of the enzyme was not the reason for the release. The CALB production level was further improved by optimizing the culture medium. Under the optimized conditions, the CALB in the culture supernatant amounted to 550 mg/L. The recombinant CALB was purified from the culture supernatant, yielding 5.67 mg of purified CALB from 50 mL of culture. N-terminal sequencing and ESI-MS analyses showed proper removal of the pelB signal sequence and the correct molecular weight of the protein, respectively, confirming the structural integrity of the recombinant CALB. The kinetic parameters towards p-nitrophenylbutyrate and the enantiomeric selectivity on rac-1-phenylethylacetate of the recombinant CALB were consistent with those of the authentic CALB. This is the first example of E. coli-based extracellular production of a CALB enzyme without extra amino acid residues.