Surface charge engineering of PQQ glucose dehydrogenase for downstream processing

The ion-exchange chromatography behavior of recombinant glucose dehydrogenase harboring pyrroloquinoline quinone (PQQGDH) was modified to greatly simplify its purification. The surface charge of PQQGDH was engineered by either fusing a three-arginine tail to the C-terminus of PQQGDH (PQQGDH+Arg3) or by substituting three residues exposed on the surface of the enzyme to Arg by site-directed mutagenesis (3RPQQGDH). During cation exchange chromatography, both surface charge-engineered enzymes eluted at much higher salt concentrations than the wild-type enzyme. After the chromatography purification step, both PQQGDH+Arg3 and 3RPQQGDH appeared as single bands on SDS-PAGE, while extra bands appeared with the wild-type protein sample. Although all tested kinetic parameters of both engineered enzymes are similar to those of wild type, both modifications resulted in enzymes with increased thermal stability. Our achievements have resulted in the greater production of an improved quality PQQGDH by a simplified process.     

Construction of multi-chimeric pyrroloquinoline quinone glucose dehydrogenase with improved enzymatic properties and application in glucose monitoring

A multi-chimeric enzyme was constructed by combining the protein regions responsible for the enzymatic properties of Escherichia coli and Acinetobacter calcoaceticus pyrroloquinoline quinone glucose dehydrogenase (PQQGDH). The constructed multi-chimeric PQQGDH showed increased co-factor binding stability, thermal stability, an alteration in substrate specificity and a 10-fold increase in the K _m value for glucose compared with the wild-type E. coli PQQGDH. The cumulative effect of each introduced protein region on the improvement of enzymatic properties was observed. The application of the multi-chimeric PQQGDH in amperometric glucose sensor construction achieved an expanded dynamic range together with increased operational stability and narrower substrate specificity. The glucose sensor can measure glucose from 5 to 40 mM, suggesting its potential for the direct measurement of high blood-glucose levels in diabetic patients.     

Simultaneous synthesis of 2‐phenylethanol and L‐homophenylalanine using aromatic transaminase with yeast Ehrlich pathway

2‐Phenylethanol is a widely used aroma compound with rose‐like fragrance and L ‐homophenylalanine is a building block of angiotensin‐converting enzyme (ACE) inhibitor. 2‐phenylethanol and L ‐homophenylalanine were synthesized simultaneously with high yield from 2‐oxo‐4‐phenylbutyric acid and L ‐phenylalanine, respectively. A recombinant Escherichia coli harboring a coupled reaction pathway comprising of aromatic transaminase, phenylpyruvate decarboxylase, carbonyl reductase, and glucose dehydrogenase (GDH) was constructed. In the coupled reaction pathway, the transaminase reaction was coupled with the Ehrlich pathway of yeast; (1) a phenylpyruvate decarboxylase (YDR380W) as the enzyme to generate the substrate for the carbonyl reductase from phenylpyruvate (i.e., byproduct of the transaminase reaction) and to shift the reaction equilibrium of the transaminase reaction, and (2) a carbonyl reductase (YGL157W) to produce the 2‐phenylethanol. Selecting the right carbonyl reductase showing the highest activity on phenylacetaldehyde with narrow substrate specificity was the key to success of the constructing the coupling reaction. In addition, NADPH regeneration was achieved by incorporating the GDH from Bacillus subtilis in the coupled reaction pathway. Based on 40 mM of L ‐phenylalanine used, about 96% final product conversion yield of 2‐phenylethanol was achieved using the recombinant E. coli. Biotechnol. Bioeng. 2009;102: 1323–1329. © 2008 Wiley Periodicals, Inc.     

Improved substrate specificity of water-soluble pyrroloquinoline quinone glucose dehydrogenase by a peptide ligand

A new approach in altering the substrate specificity of enzyme is proposed using glucose dehydrogenase, with pyrroroquinoine quinone (PQQGDH) as co-factor, as the model. This approach is based on the selection of random peptide phage displayed library. Using an M13 phage-display random peptide library, we have selected peptide ligands. Among the peptide ligands, a 7-mer peptide, composed of Thr-Thr-Ala-Thr-Glu-Tyr-Ser, caused PQQGDH substrate specificity to decrease significantly toward disaccharides, such as maltose and lactose, while a smaller effect was observed toward glucose. Consequently, this peptide narrowed the substrate specificity of PQQGDH, without a significant loss of the enzyme activity.     

Over expression of PQQ glucose dehydrogenase in Escherichia coli under holo enzyme forming condition

Summary The over expression of PQQ glucose dehydrogenase PQQGDH was investigated. The level of PQQGDH expressed in E.coli PP2418/pGEc1 was more than 10 fold when the cultivation was carried out under holo enzyme forming condition in the presence of 600 nM of PQQ and 10 mM of MgCl₂, compared with those of apo condition. It may be due to the difference in thermal stability of apo and holo PQQGDH.     

Engineering of Phosphoserine Aminotransferase Increases the Conversion of l‐Homoserine to 4‐Hydroxy‐2‐ketobutyrate in a Glycerol‐Independent Pathway of 1,3‐Propanediol Production from Glucose

Phosphoserine aminotransferase (SerC) from Escherichia coli (E. coli) MG1655 is engineered to catalyze the deamination of homoserine to 4‐hydroxy‐2‐ketobutyrate, a key reaction in producing 1,3‐propanediol (1,3‐PDO) from glucose in a novel glycerol‐independent metabolic pathway. To this end, a computation‐based rational approach is used to change the substrate specificity of SerC from l ‐phosphoserine to l ‐homoserine. In this approach, molecular dynamics simulations and virtual screening are combined to predict mutation sites. The enzyme activity of the best mutant, SerC_R42W/R77W, is successfully improved by 4.2‐fold in comparison to the wild type when l ‐homoserine is used as the substrate, while its activity toward the natural substrate l ‐phosphoserine is completely deactivated. To validate the effects of the mutant on 1,3‐PDO production, the “homoserine to 1,3‐PDO” pathway is constructed in E. coli by coexpression of SerC_R42W/R77W with pyruvate decarboxylase and alcohol dehydrogenase. The resulting mutant strain achieves the production of 3.03 g L^?1 1,3‐PDO in fed‐batch fermentation, which is 13‐fold higher than the wild‐type strain and represents an important step forward to realize the promise of the glycerol‐independent synthetic pathway for 1,3‐PDO production from glucose.     

Modular pathway engineering of key carbon‐precursor supply‐pathways for improved N‐acetylneuraminic acid production in Bacillus subtilis

N‐acetylneuraminic acid (NeuAc) is widely used as a nutraceutical for facilitating infant brain development, maintaining brain health, and enhancing immunity. Currently, NeuAc is mainly produced by extraction from egg yolk and milk, or via chemical synthesis. However, its low concentration in natural resources and its non‐ecofriendly chemical synthesis result in insufficient NeuAc production and environmental pollution, respectively. In this study, improved NeuAc production was attained via modular pathway engineering of the supply pathways of two key precursors—N‐acetylglucosamine (GlcNAc) and phosphoenolpyruvate (PEP)—and by balancing NeuAc biosynthesis and cell growth in engineered Bacillus subtilis. Specifically, we used a previously constructed GlcNAc‐producing B. subtilis as the initial host for NeuAc biosynthesis. First, we constructed a de novo NeuAc biosynthetic pathway utilizing glucose by coexpressing glucosamine‐6‐phosphate acetyl‐transferase (GNA1), N‐acetylglucosamine 2‐epimerase (AGE), and N‐acetylneuraminic acid synthase (NeuB), resulting in 0.33 g/l NeuAc production. Next, to balance the supply of the two key precursors for NeuAc biosynthesis, modular pathway engineering was performed. The optimal strategy for balancing the GlcNAc module and PEP supply module involved the use of an engineered, unique glucose and malate coutilization pathway in B. subtilis, supplied with both glucose (for the GlcNAc moiety) and malate (for the PEP moiety) at high strength. This led to 1.65 g/L NeuAc production, representing a 5.0‐fold improvement over the existing methods. Furthermore, to enhance the NeuAc yield on cell, glucose and malate coutilization pathways were engineered to balance NeuAc biosynthesis and cell growth via the blocking of glycolysis, the introduction of the Entner–Doudoroff pathway, and the overexpression of the malic enzyme YtsJ. NeuAc titer reached 2.18 g/L, with 0.38 g/g dry cell weight NeuAc yield on cell, which represented a 1.32‐fold and 2.64‐fold improvement over the existing methods, respectively. The strategy of modular pathway engineering of key carbon precursor supply pathways via engineering of the unique glucose‐malate coutilization pathway in B. subtilis should be generically applicable for engineering of B. subtilis for the production of other important biomolecules. Our study also provides a good starting point for further metabolic engineering to achieve industrial production of NeuAc by a Generally Regarded As Safe bacterial strain.     

Stabilization of pyrroloquinoline quinone glucose dehydrogenase by cross-linking chemical modification

Summary Cross-linking chemical modification of pyrroloquinoline quinone (PQQ) glucose dehydrogenase (GDH) by glutaraldehyde was carried out and its stability was analyzed. Although native PQQGDH was inactivated within 30 min at a higher temperature than 50 °C, cross-linked PQQGDH retained more than 40% of initial activity even after 30 min of incubation at 54 °C. In addition to the increase in thermal stability, cross-linked PQQGDH gained high EDTA tolerance. The stabilization may be achieved by increased the rigidity of PQQGDH holo enzyme conformation.     

Glu742 substitution to Lys enhances the EDTA tolerance ofEscherichia coli PQQ glucose dehydrogenase

Summary Based on homology analysis of the PQQ (pyrroloquinoline quinone) glucose dehydrogenase (PQQGDH) gene fromEscherichia coli andAcinetobacter calcoaceticus, Glu742 was substituted to Lys by site directed mutagenesis of theE. coli PQQGDH gene (gcd). The mutant enzyme, E742K showed higher tolerance towards EDTA inactivation than wild type PQQGDH. This is the first mutagenesis study of putative a PQQ binding site in PQQ enzyme.     

Development and evaluation of efficient recombinant Escherichia coli strains for the production of 3‐hydroxypropionic acid from glycerol

3‐Hydroxypropionic acid (3‐HP) is a commercially valuable chemical with the potential to be a key building block for deriving many industrially important chemicals. However, its biological production has not been well documented. Our previous study demonstrated the feasibility of producing 3‐HP from glycerol using the recombinant Escherichia coli SH254 expressing glycerol dehydratase (DhaB) and aldehyde dehydrogenase (AldH), and reported that an “imbalance between the two enzymes” and the “instability of the first enzyme DhaB” were the major factors limiting 3‐HP production. In this study, the efficiency of the recombinant strain(s) was improved by expressing DhaB and AldH in two compatible isopropyl‐thio‐β‐galactoside (IPTG) inducible plasmids along with glycerol dehydratase reactivase (GDR). The expression levels of the two proteins were measured. It was found that the changes in protein expression were associated with their enzymatic activity and balance. While cloning an alternate aldehyde dehydrogenase (ALDH), α‐ketoglutaric semialdehyde dehydrogenase (KGSADH), instead of AldH, the recombinant E. coli SH‐BGK1 showed the highest level of 3‐HP production (2.8 g/L) under shake‐flask conditions. When an aerobic fed‐batch process was carried out under bioreactor conditions at pH 7.0, the recombinant SH‐BGK1 produced 38.7 g 3‐HP/L with an average yield of 35%. This article reports the highest level of 3‐HP production from glycerol thus far. Biotechnol. Bioeng. 2009; 104: 729–739 © 2009 Wiley Periodicals, Inc.     

Synthesis of Optically Active Diols by Escherichia coli Transformant Cells that Express the Glycerol Dehydrogenase Gene of Hansenula polymorphaDL‐1

Chiral alcohols are useful as intermediates for the synthesis of drugs. In the production of chiral alcohols, microbial enzymes are promising since high optical purity is required. Under these conditions, the reaction by resting cells is more convenient and inexpensive than by an enzyme reaction. Chiral 1,2‐propanediol and 2,3‐butanediol were obtained using cells expressing the enzyme which demonstrated high stereospecificity. By means of recombinant cells expressing the glycerol dehydrogenase of Hansenula polymorpha DL‐1, the medium was enriched with (S)‐1,2‐propanediol (98 % enantiometric excess, e.e.) during a 24‐h incubation, whereas the (R)‐form was removed from 100 mM of the racemate (R:S = 1:1). For an asymmetric reduction, a recombinant was constructed which also expressed the glucose dehydrogenase gene of Bacillus subtilis origin as an NADH reproducer. In the resting cell reaction, the pH control at 7.5 promoted the conversion from ketone to alcohol. (2R,3R)‐2,3‐butanediol (e.e. > 99.9 %; 308 mM) was produced from 800 mM acetoin (R:S = 3:4); (R)‐1,2‐propanediol (e.e. > 99.9 %; 550 mM) from 800 mM acetol in a 33‐h incubation by the addition of glucose and ketone with pH control. In this reaction, (S)‐forms of both 2,3‐butanediol and 1,2‐propanediol were not produced. The pH control and feeding of the substrates were uncomplicated. The production process of the chiral alcohol by the recombinants which expresses glycerol dehydrogenase proved convenient.     

Engineering a chimeric pyrroloquinoline quinone glucose dehydrogenase: improvement of EDTA tolerance, thermal stability and substrate specificity

An engineered Escherichia coli PQQ glucose dehydrogenase (PQQGDH) with improved enzymatic characteristics was constructed by substituting and combining the gene-encoding protein regions responsible for EDTA tolerance, thermal stability and substrate specificity. The protein region responsible for complete EDTA tolerance in Acinetobacter calcoaceticus, which is recognized as the indicator of high stability in co-factor binding, was elucidated. The region is located between 32 and 59% from the N-terminus of A. calcoaceticus PQQGDH(A27 region) and also corresponds to the same position from 32 to 59% from the N-terminus in E. coli PQQGDH, though E. coli PQQGDH is EDTA sensitive. We previously reported that the C-terminal 3% region of A. calcoaceticus (A3 region) played an important role in the increase of thermal stability, and that His775Asn substitution in E. coli PQQGDH resulted in an increase in the substrate specificity of E. coli PQQGDH towards glucose. Based on these findings, chimeric and/or mutated PQQGDHs, E97A3 H775N, E32A27E41 H782N, E32A27E38A3 and E32A27E38A3 H782N were constructed to investigate the compatibility of two protein regions and one amino acid substitution. His775 substitution to Asn corresponded to His782 substitution to Asn (H782N) in chimeric enzymes harbouring the A27 region. Since all the chimeric PQQGDHs harbouring the A27 region were EDTA tolerant, the A27 region was found to be compatible with the other region and substituted amino acid responsible for the improvement of enzymatic properties. The contribution of the A3 region to thermal stability complemented the decrease in the thermal stability due to the His775 or His782 substitution to Asn. E32A27E38A3 H782N, which harbours all the above mentioned three regions, showed improved EDTA tolerance, thermal stability and substrate specificity. These results suggested a strategy for the construction of a semi-artificial enzyme by substituting and combining the gene-encoding protein regions responsible for the improvement of enzyme characteristics. The characteristics of constructed chimeric PQQGDH are discussed based on the predicted model, beta-propeller structure.     

Zymobacter palmae pyruvate decarboxylase production process development: Cloning in Escherichia coli,fed‐batch culture and purification

Pyruvate decarboxylase (PDC) is responsible for the decarboxylation of pyruvate, producing acetaldehyde and carbon dioxide and is of high interest for industrial applications. PDC is a very powerful tool in the enzymatic synthesis of chiral amines by combining it with transaminases when alanine is used as amine donor. However, one of the main drawback that hampers its use in biocatalysis is its production and the downstream processing on scale. In this paper, a production process of PDC from Zymobacter palmae has been developed. The enzyme has been cloned and overexpressed in Escherichia coli. It is presented, for the first time, the evaluation of the production of recombinant PDC in a bench‐scale bioreactor, applying a substrate‐limiting fed‐batch strategy which led to a volumetric productivity and a final PDC specific activity of 6942 U L^?1h^?1 and 3677 U gDCW^?1 (dry cell weight). Finally, PDC was purified in fast protein liquid chromatography equipment by ion exchange chromatography. The developed purification process resulted in 100% purification yield and a purification factor of 3.8.     

Characterization and high‐yield production of non‐N‐glycosylated recombinant human BCMA‐Fc in Pichia pastoris

B‐cell maturation antigen (BCMA) fused at the C‐terminus to the Fc portion of human IgG1 (BCMA‐Fc) blocks B‐cell activating factor (BAFF) and proliferation‐inducing ligand (APRIL)‐mediated B‐cell activation, leading to immune disorders. The fusion protein has been cloned and produced by several engineering cell lines. To reduce cost and enhance production, we attempted to express recombinant human BCMA‐Fc (rhBCMA‐Fc) in Pichia pastoris under the control of the AOX1 methanol‐inducible promoter. To produce the target protein with uniform molecular weight and reduced immunogenicity, we mutated two predicted N‐linked glycosylation sites. The secretory yield was improved by codon optimization of the target gene sequence. After fed‐batch fermentation under optimized conditions, the highest yield (207 mg/L) of rhBCMA‐Fc was obtained with high productivity (3.45 mg/L/h). The purified functional rhBCMA‐Fc possessed high‐binding affinity to APRIL and dose‐dependent inhibition of APRIL‐induced proliferative activity in vitro through three‐step purification. Thus, this yeast‐derived expression method could be a low‐cost and effective alternative to the production of rhBCMA‐Fc in mammalian cell lines.     

Engineering Escherichia coli for renewable production of the 5‐carbon polyamide building‐blocks 5‐aminovalerate and glutarate

Through metabolic pathway engineering, novel microbial biocatalysts can be engineered to convert renewable resources into useful chemicals, including monomer building‐blocks for bioplastics production. Here we describe the systematic engineering of Escherichia coli to produce, as individual products, two 5‐carbon polyamide building blocks, namely 5‐aminovalerate (AMV) and glutarate. The modular pathways were derived using “parts” from the natural lysine degradation pathway of Pseudomonas putida KT2440. Endogenous over‐production of the required precursor, lysine, was first achieved through metabolic deregulation of its biosynthesis pathway by introducing feedback resistant mutants of aspartate kinase III and dihydrodipicolinate synthase. Further disruption of native lysine decarboxylase activity (by deleting cadA and ldcC) limited cadaverine by‐product formation, enabling lysine production to 2.25 g/L at a glucose yield of 138 mmol/mol (18% of theoretical). Co‐expression of lysine monooxygenase and 5‐aminovaleramide amidohydrolase (encoded by davBA) then resulted in the production of 0.86 g/L AMV in 48 h. Finally, the additional co‐expression of glutaric semialdehyde dehydrogenase and 5‐aminovalerate aminotransferase (encoded by davDT) led to the production of 0.82 g/L glutarate under the same conditions. At this output, yields on glucose were 71 and 68 mmol/mol for AMV and glutarate (9.5 and 9.1% of theoretical), respectively. These findings further expand the number and diversity of polyamide monomers that can be derived directly from renewable resources. Biotechnol. Bioeng. 2013; 110: 1726–1734. © 2013 Wiley Periodicals, Inc.     

Development of production and purification processes of recombinant fragment of pneumococcal surface protein A in <Emphasis Type="Italic">Escherichia coli</Emphasis> using different carbon sources and chromatography sequences

Pneumococcal surface protein A (PspA) is essential for Streptococcus pneumoniae virulence and its use either as a novel pneumococcal vaccine or as carrier in a conjugate vaccine would improve the protection and the coverage of the vaccine. Within this context, the development of scalable production and purification processes of His-tagged recombinant fragment of PspA from clade 3 (rfPspA3) in Escherichia coli BL21(DE3) was proposed. Fed-batch production was performed using chemically defined medium with glucose or glycerol as carbon source. Although the use of glycerol led to lower acetate production, the concentration of cells were similar at the end of both fed-batches, reaching high cell density of E. coli (62 g dry cell weight/L), and the rfPspA3 production was higher with glucose (3.48 g/L) than with glycerol (2.97 g/L). A study of downstream process was also carried out, including cell disruption and clarification steps. Normally, the first chromatography step for purification of His-tagged proteins is metal affinity. However, the purification design using anion exchange followed by metal affinity gave better results for rfPspA3 than the opposite sequence. Performing this new design of chromatography steps, rfPspA3 was obtained with 95.5% and 75.9% purity, respectively, from glucose and glycerol culture. Finally, after cation exchange chromatography, rfPspA3 purity reached 96.5% and 90.6%, respectively, from glucose and glycerol culture, and the protein was shown to have the expected alpha-helix secondary structure.     

Ultra‐stable phosphoglucose isomerase through immobilization of cellulose‐binding module‐tagged thermophilic enzyme on low‐cost high‐capacity cellulosic adsorbent

One‐step enzyme purification and immobilization were developed based on simple adsorption of a family 3 cellulose‐binding module (CBM)‐tagged protein on the external surface of high‐capacity regenerated amorphous cellulose (RAC). An open reading frame (ORF) Cthe0217 encoding a putative phosphoglucose isomerase (PGI, EC 5.3.1.9) from a thermophilic bacterium Clostridium thermocellum was cloned and the recombinant proteins with or without CBM were over‐expressed in Escherichia coli. The rate constant (k_cat) and Michaelis–Menten constant (K_m) of CBM‐free PGI at 60°C were 2,765 s^?1 and 2.89 mM, respectively. PGI was stable at a high protein concentration of 0.1 g/L but deactivated rapidly at low concentrations. Immobilized CBM (iCBM)‐PGI on RAC was extremely stable at ～60°C, nearly independent of its mass concentration in bulk solution, because its local concentration on the solid support was constant. iCBM‐PGI at a low concentration of 0.001 g/L had a half‐life time of 190 h, approximately 80‐fold of that of free PGI. Total turn‐over number of iCBM‐PGI was as high as 1.1 × 10⁹ mole of product per mole of enzyme at 60°C. These results suggest that a combination of low‐cost enzyme immobilization and thermoenzyme led to an ultra‐stable enzyme building block suitable for cell‐free synthetic pathway biotransformation that can implement complicated biochemical reactions in vitro. © 2011 American Institute of Chemical Engineers Biotechnol. Prog., 2011.     

Mouse recombinant phenylalanine monooxygenase and the S‐oxygenation of thioether substrates

The substrate specificity of mouse recombinant phenylalanine monooxygenase (mPAH) has been investigated with respect to the mucoactive drug, S‐carboxymethyl‐L ‐cysteine (SCMC) and its thioether metabolites. Phenylalanine monooxygenase was shown to be able to catalyze the S‐oxygenation of SCMC, its decarboxylated metabolite, S‐methyl‐L ‐cysteine and both their corresponding N‐acetylated forms. However, thiodiglycolic acid was found not to be a substrate. The enzyme profiles for both phenylalanine and SCMC showed Michaelis‐Menten with noncompetitive substrate inhibition for both the substrate‐activated and the lysophosphatidylcholine‐activated mPAH assays. The tetrameric enzyme was shown to undergo posttranslational activation by preincubation with substrate, lysophosphatidylcholine, N‐ethylmaleimide (a thiol alkylating agent), and the proteolytic enzymes α‐chymotrypsin and trypsin. Similar posttranslational activation of PAH activity in the rat and human has also been reported. These results suggest that in the mouse, PAH was responsible for the S‐oxidation of SCMC and that the mouse models of the hyperphenylalaninemias may be a potential tool in the investigation of the S‐oxidation polymorphism in man. © 2009 Wiley Periodicals, Inc. J Biochem Mol Toxicol 23:119–124, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jbt.20274     

Recombinant overexpression of camel hepcidin cDNA in Pichia pastoris: purification and characterization of the polyHis‐tagged peptide HepcD‐His

Hepcidin, a liver‐expressed antimicrobial peptide, has been demonstrated to act as an iron regulatory hormone as well as to exert a wide spectrum of antimicrobial activity. The aim of this work was the expression, as secreted peptide, purification, and characterization of a new recombinant polyHis‐tagged camel hepcidin (HepcD‐His) in yeast Pichia pastoris . The use of this eukaryotic expression system, for the production of HepcD‐His, having 6 histidine residues at its C terminus, was simpler and more efficient compared with the use of the prokaryotic system Escherichia  coli . Indeed, a single purification step was required to isolate the soluble hepcidin with purity estimated more that 94% and a yield of 2.8 against 0.2 mg/L for the E coli system. Matrix‐assisted laser desorption/ionization time‐of‐flight (TOF)/TOF mass spectrometry of the purified HepcD‐His showed 2 major peaks at m /z 4524.64 and 4634.56 corresponding to camel hepcidin with 39 and 40 amino acids. Evaluation of disulfide bond connectivity with the Ellman method showed an absence of free thiol groups, testifying that the 8 cysteine residues in the peptide are displayed, forming 4 disulfide bridges. Circular dichroism spectroscopy showed that camel hepcidin structure was significantly modified at high temperature of 90°C and returns to its original structure when incubation temperature drops back to 20°C. Interestingly, this peptide showed also a greater bactericidal activity, at low concentration of 9.5μM, against E coli , than the synthetic analog DH3. Thus, the production, at a large scale, of the recombinant camel hepcidin, HepcD‐His, may be helpful for future therapeutic applications including bacterial infection diseases.     

Three‐Enzyme Phosphorylase Cascade for Integrated Production of Short‐Chain Cellodextrins

Cellodextrins are linear β‐1,4‐gluco‐oligosaccharides that are soluble in water up to a degree of polymerization (DP) of ≈6. Soluble cellodextrins have promising applications as nutritional ingredients. A DP‐controlled, bottom‐up synthesis from expedient substrates is desired for their bulk production. Here, a three‐enzyme glycoside phosphorylase cascade is developed for the conversion of sucrose and glucose into short‐chain (soluble) cellodextrins (DP range 3–6). The cascade reaction involves iterative β‐1,4‐glucosylation of glucose from α‐glucose 1‐phosphate (αGlc1‐P) donor that is formed in situ from sucrose and phosphate. With final concentration and yield of the soluble cellodextrins set as targets for biocatalytic synthesis, three major factors of reaction efficiency are identified and partly optimized: the ratio of enzyme activity, the ratio of sucrose and glucose, and the phosphate concentration used. The efficient use of the phosphate/αGlc1‐P shuttle for cellodextrin production is demonstrated and the soluble product at 40 g L^?1 is obtained under near‐complete utilization of the donor substrate offered (88 mol% from 200 mm sucrose). The productivity is 16 g (L h)^?1. Through a simple two‐step route, the soluble cellodextrins are recovered from the reaction mixture in ≥95% purity and ≈92% yield. Overall, this study provides the basis for their integrated production.