Fermentation conditions for high-level expression of the tac-promoter-controlled calf prochymosin cDNA in Escherichia coli HB101

Skimmed milk as an alternative for IPTG in induction of recombinant protein expression

Cost-effectiveness is an important issue in biotechnological manufacturing industry and using alternative cheap materials with the same benefits has been noticed in most literatures. Isopropyl β-d-1-thiogalactopyranoside (IPTG), a well-known chemical element for induction of protein expression, has several disadvantages such as high expense and toxicity. In this study, we aimed to introduce skimmed milk as an alternative material for protein expression by induction of lac operon. In this way, Escherichia coli BL21 (DE3) bacteria were induced using 1 mM IPTG or 1.0% (w/v) skimmed milk. Protein purification was performed using Ni-NTA (nickel-nitrilotriacetic acid) for His-tagged recombinant proteins and protein purity was evaluated by SDS-PAGE. Results showed high level of recombinant protein expression using skimmed milk, and interestingly, the growth rate of bacteria improved. Our findings suggested that skimmed milk can be a suitable alternative for induction of recombinant protein expression, which has advantages such as more availability and affordability, in comparison to IPTG supplementation.

Optimization of the crystallizability of a single-chain antibody fragment

Single-chain variable antibody fragments (scFvs) are molecules with immense therapeutic and diagnostic potential. Knowledge of their three-dimensional structure is important for understanding their antigen-binding mode as well as for protein-engineering approaches such as antibody humanization. A major obstacle to the crystallization of single-chain variable antibody fragments is their relatively poor homogeneity caused by spontaneous oligomerization. A new approach to optimization of the crystallizability of single-chain variable antibody fragments is demonstrated using a representative single-chain variable fragment derived from the anti-CD3 antibody MEM-57. A Thermofluor-based assay was utilized to screen for optimal conditions for antibody-fragment stability and homogeneity. Such an optimization of the protein storage buffer led to a significantly improved ability of the scFv MEM-57 to yield crystals.

Effect of Inducers on the Production of 5‐Aminolevulinic Acid by RecombinantEscherichia coli

Aminolevulinic acid (ALA) was produced by recombinant Escherichia coli BL21(DE3) (pET28-A.R-hemA) harboring the ALA synthase gene (hemA) from Agrobacterium radiobacter zju-0121. The effects of inducers on the ALA synthase activity and ALA productivity were evaluated. The results indicated that a low isopropyl-beta-D-thiogalactoside (IPTG) concentration (0.05 mmol/L) was favorable for high expression of ALA synthase, which resulted in higher ALA productivity. For metabolic engineering applications, lactose was a better substitute of IPTG for active enzyme expression. When lactose concentration was 5 mmol/L, the specific ALA synthase activity and ALA productivity reached 16.7 nmol/(min . mg of protein) and 1.15 g/L, respectively, which were about 15% and 43% higher than those induced by IPTG.

Effect of postinduction nutrient feed composition and use of lactose as inducer during production of thermostable xylanase in Escherichia coli glucose-limited fed-batch cultivations

Escherichia coli is a microorganism routinely used in the production of heterologous proteins. The overexpression of a xylanase (Xyn 10 A Delta NC), which originated from the thermophile Rhodothermus marinus cloned under the control of the strong T7/lac promoter in a defined medium (mAT) using a substrate-limited feed strategy, was however shown to impose a significant metabolic burden on host cells. This resulted in a decreased cell growth rate and ultimately also a decreased target protein production. The investigation hence centers on the effect of some selected nutrient feed additives (amino acid [Cys] or TCA-intermediates [citrate, succinate, malate]) used to relieve the metabolic burden imposed during the feeding and postinduction phases of these glucose-limited fed-batch cultivations. The use of either succinic acid or malic acid as feed-additives resulted in an increase in production of approximately 40% of the heterologous thermostable xylanase. Furthermore, use of lactose as an alternative inducer of the T7/lac promoter was also proven to be a suitable strategy that significantly prolonged the heterologous protein production phase as compared with induction using isopropyl beta-D-thiogalactopyranoside (IPTG).

Production of the kringle fragments of human apolipoprotein(a) by continuous lactose induction strategy

A novel lactose induction strategy for the production of rhLK68, the kringle fragments of human apolipoprotein(a) (apo(a)) as a novel anti-angiogenic protein, was investigated. A scale-up of the production was accompanied by a decrease in expression level, and severe aggregation occurred during the solubilization of rhLK68 from the inclusion body during a conventional single introduction of lactose. To overcome this problem, a continuous induction strategy was applied where lactose was mixed with glycerol and fed continuously in a dissolved oxygen (DO)-stat manner. With the sub-optimal feed medium consisted of 1:50 of lactose/glycerol (w/w), the expression level reached 16% of the total cellular protein, which was 1.6-fold higher than that obtained from the conventional lactose induction. Moreover, the solubilization yield of rhLK68 from the inclusion body increased from 30 +/- 5 to 85 +/- 3% compared to the conventional single introduction of lactose. This result suggests that the continuous lactose induction strategy beneficially influenced the expression level of rhLK68 and the quality of its inclusion body.

High-level expression of a fungal pyranose oxidase in high cell-density fed-batch cultivations of Escherichia coli using lactose as inducer

Expression of a recombinant pyranose oxidase (P2O) from the basidiomycete Trametes ochracea has been increased 10-fold in shaking flask cultures of Escherichia coli BL21(DE3) harboring plasmid pSE33 by optimizing the composition of the culture medium using an experimental design approach. Inexpensive lactose was used as a medium component and inducer of expression of the P2O gene, which is under the control of a trc promoter. The expression system was studied in detail in batch and fed-batch cultivations with the aim to improve the expression level of active recombinant protein and to minimize the formation of inclusion bodies. In batch cultivations, the highest specific P2O activity of 0.9 U (mg of soluble protein)(-1) was measured in oxygen-limited cultures grown at 25 degrees C. The highest overall volumetric productivity of 33 mg of active P2O per liter and hour (corresponding to 345U (L h)(-1)) has been determined in a high-density fed-batch process with a feed-forward exponential feeding strategy. During the fed-batch process, lactose was added intermittently to the culture. A final biomass concentration of 33 g L(-1) (based on cell dry weight) was obtained. Compared to shaking flask cultures in not optimized culture media, the overall volumetric P2O productivity has been improved by a factor of 110 using the fed-batch strategy and the optimized culture medium. Recombinant P2O was expressed in the cytoplasm with 9% of the total soluble protein being active P2O. In terms of physical and enzyme kinetic properties, the purified recombinant P2O was found to be similar to the previously published data of P2O isolated from its original host.

Cheese whey-induced high-cell-density production of recombinant proteins in Escherichia coli

BACKGROUND: Use of lactose-rich concentrates from dairy processes for the induction of recombinant gene's expression has not received much attention although they are interesting low cost substrates for production of recombinant enzymes. Applicability of dairy waste for induction of recombinant genes in Escherichia coli was studied. Clones expressing Lactobacillus phage muramidase and Lactobacillus alcohol dehydrogenase were used for the experiments. RESULTS: Shake flask cultivations in mineral salt medium showed that cheese whey or deproteinised whey induced gene expression as efficiently as IPTG (isopropyl-beta-D-thiogalactopyranoside) or pure lactose. Addition of yeast extract or proteolytically degraded whey proteins did not improve the recombinant protein yield. In contrast, addition of yeast extract to the well-balanced mineral salt medium decreased the product yield. Feeding with glycerol provided sufficient amount of easily assimilable carbon source during the induction period without preventing lactose intake and induction by lactose. High-cell-density fed-batch cultivations showed that product yields comparable to IPTG-induction can be achieved by feeding bacteria with a mixture of glycerol and concentrated whey permeate during the induction. CONCLUSION: Whey and concentrated whey permeate can be applied as an alternative inducer in recombinant high-cell-density fed-batch fermentations. The yield of the recombinant product was comparable to fermentations induced by IPTG. In low-cell-density shake flask experiments the yield was higher with whey or whey permeate than with IPTG.

Automatic inducer addition and harvesting of recombinant Escherichia coli cultures based on indirect on-line estimation of biomass concentration and specific growth rate

This article describes a novel bioreactor configuration for production optimization of recombinant proteins in Escherichia coli. Inducer addition and harvesting are controlled on-line based on indirect estimation of biomass concentration and specific growth rate from addition of NaOH to maintain constant pH. When either a predetermined biomass concentration is reached or the cultures have obtained, a constant specific growth rate inducer is introduced automatically. The induction period is ended by automatic harvesting of the cultures either at a predetermined biomass concentration or when substrate (in this study glucose) is depleted, detected as an increase of pH, or dissolved oxygen tension. During harvesting, metabolic activities are quenched within 3 min by cooling of the cell suspension. The system has been used to optimize expression of glutathione S-transferase (GST) fusion protein of the ligand binding domain of mouse peroxisome proliferator-activated receptor, GST-PPARalpha LBD. Total yield of GST-PPARalpha LBD was independent of the time of inducer addition as long as the length of induction period corresponded to at least 0.25 cell divisions while the yield of soluble GST-PPARalpha LBD, the only active form, increased with the length of induction period. Highest yields were obtained when the inducer was added at low cell concentration as soon as constant specific growth rate was detected, resulting in induction periods corresponding to 3.4 +/- 0.4 cell divisions. The specific growth rate remained almost constant for one cell division after inducer addition, whereafter it decreased. No decrease of specific growth rate was observed when inducer was added in the lag-phase, and no soluble protein was produced. These results suggest that solely soluble GST-PPARalpha LBD acts as a growth inhibitor and that GST-PPARalpha LBD is expressed predominantly as inclusion bodies immediately after inducer addition whereas the proportion expressed as soluble protein is increased after 1 h of induction. Compared to the procedures, which are generally used for protein expression in the laboratory, this system is less labor intensive, it automatically provides recording of biomass concentration and specific growth rate, and it allows direct comparisons between expression of different proteins and performance of different constructs since the induction period is linked to growth.

Effects of temperature and novobiocin on the expression of calf prochymosin gene and on plasmid copy number in recombinant Escherichia coli

Escherichia coli strain HB101 harboring an expression plasmid bearing calf prochymosin gene under the control of the tac promoter was grown in the presence of IPTG with or without novobiocin at 28 and 40 degrees C, respectively. The differential rates of synthesis of prochymosin inclusions, and, for comparison, of beta-lactamase and beta-galactosidase, as well as plasmid copy number, were determined during the first hours of steady state growth. At 28 degrees C the induced expression of prochymosin gene was almost blocked. Addition of novobiocin did not alleviate this effect. In fact, it strengthened it, and we conclude that both these additive inhibitory effects are a consequence of the decrease in negative superhelical tension of plasmid DNA to an insufficient level. At 40 degrees C the differential rate of prochymosin synthesis was markedly enhanced. Since the copy number of the expression plasmid increased approximately to the same extent, we conclude that an increase in gene dose is the cause. The stimulation of cloned heterologous gene expression at 40 degrees C and inhibition at 28 degrees C may be conveniently used in biotechnological-scale cultivations of some recombinant bacteria.

Recombinant gene expression in Escherichia coli cultivation using lactose as inducer

The use of lactose as inducer of foreign gene expression under control of the lac UV5 promoter was investigated in recombinant Escherichia coli. Chicken muscle troponin C (TnC) gene was transcripted by T7 RNA polymerase and expressed in bioreactor cultivations after a feed-forward controlled fed-batch growth phase. Cell concentrations of 22 g l-1 dry cell weight (DCW)--before induction started--were used to achieve a TnC content of 19.5% of total cell protein through an induction strategy that combined the addition of a specific lactose amount of 4.7 g g-1 DCW divided into three pulses and the addition of yeast extract (1 g l-1) together with the second and the third lactose pulses. The results presented suggest that the residual lactose concentration plays an important role on the production of the heterologous protein.

Overproduction of recombinant ribulose 1,5-bisphosphate carboxylase/oxygenase from Synechococcus sp. strain PCC6301 in glucose-controlled high-cell-density fermentations by Escherichia coli K-12

A predictive and feedback glucose feed controller, previously developed for nutrient-sufficient growth of Escherichia coli to high cell densities, was used to produce large quantities of a heterologous, cyanobacterial recombinant hexadecameric (L8S8) protein, ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) in E. coli. Culture and plasmid stability conditions were optimized to yield the production of approximately 1 g of soluble, active recombinant RubisCO per liter. Recombinant RubisCO also was produced in lactose-induced high-cell-density fermentation of E. coli K-12.

Review: optimizing inducer and culture conditions for expression of foreign proteins under the control of the lac promoter

This review examines factors which influence the expression of foreign proteins in Escherichia coli under the transcriptional control of the lac and tac promoters, and discusses conditions for maximizing the production of a foreign protein using this system. Specifically, the influence of IPTG (isopropyl-beta-D-thiogalactoside) concentration, temperature, composition of the growth medium, the point in the growth curve at which cells are induced with either IPTG or lactose, and the duration of the induction phase are discussed.

Glucose and acetate influences on the behavior of the recombinant strain Escherichia coli HB 101 (GAPDH)

This study highlights data about the production of a recombinant protein (glyceraldehyde-3-phosphate dehydrogenase) by E. coli HB 101 (GAPDH) during batch and fed-batch fermentations in a complex medium. From a small number of experiments, this strain has been characterized in terms of protein production performance and glucose and acetate influences on growth and recombinant protein production. The present results show that this strain is suitable for recombinant protein production, in fed-batch culture 55 g L-1 of biomass and 6 g L-1 of GAPDH are obtained. However this strain, and especially GAPDH overproduction is sensitive to glucose availability. During fermentations, maximum yields of GAPDH production have been obtained in batch experiments for glucose concentration of 10 g L-1, and in fed-batch experiments for glucose availability of 10 g h-1 (initial volume 1.5 L). The growth of the strain and GAPDH overproduction are also inhibited by acetate. Moreover acetate has been noted as an activator of its own formation.

Efficient use of lactose for the lac promoter-controlled overexpression of the main antigenic protein of the foot and mouth disease virus in Escherichia coli under fed-batch fermentation conditions

Derivatives of the lac promoter (tac, pac, rac) belong to the strongest bacterial promoters which are frequently used for the induced overexpression of foreign genes in Escherichia coli. However, their use in fermentation processes is strongly restricted because of the high cost of the inducer iso-propyl-beta-D-thiogalactopyranoside (IPTG). The aim of this work was to investigate the possibility of using lac-derived promoters in high cell density processes resulting in a high yield of the induced recombinant protein if glucose is the main carbon and energy source. Lactose is tested as inducer of the main antigenic coat protein (VP1) of the foot and mouth disease (FMD) virus in a T7-RNA polymerase expression system. It was shown that lactose is able to induce the expression of the recombinant gene to an amount of the VP1 protein corresponding to 20% of the total cell protein.

Overexpression of a Rhizopus delemar lipase gene in Escherichia coli

A cloned complementary deoxyribonucleic acid encoding the precursor polypeptide of an extracellular lipase from the fungus Rhizopus delemar was altered by site-directed mutagenesis to generate deoxyribonucleic acid fragments that specifically code for the polypeptides of the proenzyme and the mature form of the lipase. Attempts to produce these polypeptides in enzymatically active form in Escherichia coli revealed toxic effects toward the host. Therefore the polypeptides were expressed as inactive and insoluble forms in the cytoplasm of E. coli BL21 (DE3) cells using plasmid vector pET11-d. With this tightly regulated high-level expression system, lipase and prolipase polypeptides were produced to estimated levels of up to 21% and 15%, respectively, of total cellular protein. The insoluble polypeptides were solubilized in 8 M urea. Refolding into active forms was achieved by treatment with the redox system cystine/cysteine and dilution. Refolded mature lipase was purified to homogeneity by affinity and ion exchange chromatography. The enzyme had a specific activity comparable to that of lipase from the fungal culture. The quantities of pure enzyme obtained from a 1-L culture of E. coli exceeded those obtained from the fungal culture by a factor of at least 100. Refolded recombinant prolipase was purified essentially to homogeneity and had a specific activity similar to that of the mature enzyme. Its pH optimum was 7.5, rather than the pH 8 determined for recombinant mature lipase and for the enzyme purified from the fungal culture. Recombinant prolipase retained activity after 15 min incubation at 65 degrees C, while mature lipase retained activity only up to 45 degrees C.