Improving the soluble expression and purification of recombinant human stem cell factor (SCF) in endotoxin-free Escherichia coli by disulfide shuffling with persulfide

One-step immunoassay based on switching peptides for analyzing ochratoxin A in wines

A one-step immunoassay is presented for the detection of ochratoxin A (OTA) using an antibody complex with switching peptides. Because the switching peptides (fluorescence-labeled) were able to bind the frame region of antibodies (IgGs), they were dissociated from antibodies immediately when target analytes were bound to the binding pockets of antibodies. From the fluorescence signal measurements of switching peptides, a quantitative analysis of target analytes, via a one-step immunoassay without any washing steps, could be performed. As the first step, the binding constant (KD) of OTA to the antibodies was estimated under the continuous flow conditions of a surface plasmon resonance biosensor. Then, the optimal switching peptide, among four types of switching peptides, and the reaction condition for complex formation with the switching peptide were determined for the one-step immunoassay for OTA analysis. Additionally, the selectivity test of one-step immunoassay for OTA was carried out in comparison with phenylalanine and zearalenone. For the application to the one-step immunoassay to detect OTA in wines, two types of sample pre-treatment methods were compared: (1) a liquid extraction was carried out using chloroform as a solvent with subsequent resuspension in phosphate-buffered saline (total analysis time < 1 h); (2) direct dilution of the wine sample (total analysis time < 0.5 h). Finally, the direct dilution method was found to be effective for the one-step immunoassay based on the switching peptide assay for OTA in wines with a markedly improved total analysis time (< 0.5 h). Additionally, the assay results were compared with commercial lateral flow immunoassay.

ClearColi as a platform for untagged pneumococcal surface protein A production: cultivation strategy, bioreactor culture, and purification

Abstract

Several studies have searched for new antigens to produce pneumococcal vaccines that are more effective and could provide broader coverage, given the great number of serotypes causing pneumococcal diseases. One of the promising subunit vaccine candidates is untagged recombinant pneumococcal surface protein A (PspA4Pro), obtainable in high quantities using recombinant Escherichia coli as a microbial factory. However, lipopolysaccharides (LPS) present in E. coli cell extracts must be removed, in order to obtain the target protein at the required purity, which makes the downstream process more complex and expensive. Endotoxin-free E. coli strains, which synthesize a nontoxic mutant LPS, may offer a cost-effective alternative way to produce recombinant proteins for application as therapeutics. This paper presents an investigation of PspA4Pro production employing the endotoxin-free recombinant strain ClearColi® BL21(DE3) with different media (defined, auto-induction, and other complex media), temperatures (27, 32, and 37 °C), and inducers. In comparison to conventional E. coli cells in a defined medium, ClearColi presented similar PspA4Pro yields, with lower productivities. Complex medium formulations supplemented with salts favored PspA4Pro yields, titers, and ClearColi growth rates. Induction with isopropyl-β-d-thiogalactopyranoside (0.5 mM) and lactose (2.5 g/L) together in a defined medium at 32 °C, which appeared to be a promising cultivation strategy, was reproduced in 5 L bioreactor culture, leading to a yield of 146.0 mg PspA4Pro/g dry cell weight. After purification, the cell extract generated from ClearColi led to 98% purity PspA4Pro, which maintained secondary structure and biological function. ClearColi is a potential host for industrial recombinant protein production.

Key points

• ClearColi can produce as much PspA4Pro as conventional E. coli BL21(DE3) cells.

• 10.5 g PspA4Pro produced in ClearColi bioreactor culture using a defined medium.

• Functional PspA4Pro (98% of purity) was obtained in ClearColi bioreactor culture.

Novel Bacterial Production of Two Different Bioactive Forms of Human Stem-Cell Factor

Human stem-cell factor (hSCF) stimulates the survival, proliferation, and differentiation of hematopoietic cells by binding to the c-Kit receptor. Various applications of hSCF require the efficient and reliable production of hSCF. hSCF exists in three forms: as two membrane-spanning proteins hSCF248 and hSCF229 and truncated soluble N-terminal protein hSCF164. hSCF164 is known to be insoluble when expressed in Escherichia coli cytoplasm, requiring a complex refolding procedure. The activity of hSCF248 has never been studied. Here, we investigated novel production methods for recombinant hSCF164 and hSCF248 without the refolding process. To increase the solubility of hSCF164, maltose-binding protein (MBP) and protein disulfide isomerase b’a’ domain (PDIb’a’) tags were attached to the N-terminus of hSCF164. These fusion proteins were overexpressed in soluble form in the Origami 2(DE3) E. coli strain. These solubilization effects were enhanced at a low temperature. His-hSCF248, the poly-His tagged form of hSCF248, was expressed in a highly soluble form without a solubilization tag protein, which was unexpected because His-hSCF248 contains a transmembrane domain. hSCF164 was purified using affinity and ion-exchange chromatography, and His-hSCF248 was purified by ion-exchange and gel filtration chromatography. The purified proteins stimulated the proliferation of TF-1 cells. Interestingly, the EC₅₀ value of His-hSCF248 was 1 pg/mL, 100-fold lower than 9 ng/mL hSCF164. Additionally, His-hSCF248 decreased the doubling time, increased the proportion of S and G2/M stages in the cell cycle, and increased the c-Myc expression at a 1000-fold lower concentration than hSCF164. In conclusion, His-hSCF248 was expressed in a soluble form in E. coli and had stronger activity than hSCF164. The molecular chaperone, MBP, enabled the soluble overexpression of hSCF164.

Surface display of sialyltransferase on the outer membrane of Escherichia coli and ClearColi

α2,3-Sialyltransferase from Pasteurella multocida (PmST1) is an enzyme that transfers a sialyl group of donor substrates to an acceptor substrate called N-acetyl-d-lactosamine (LacNAc). In this study PmST1 was expressed on the outer membrane of wildtype Escherichia coli (BL21) with lipopolysaccharide (LPS) and ClearColi with no LPS, and then the enzyme activity and expression level of PmST1 were compared. As the first step, the expression levels of PmST1 on the outer membranes of wildtype E. coli (BL21) and ClearColi were compared according to the IPTG induction time, and the absolute amount of surface-displayed PmST1 was calculated using densitometry of SDS-PAGE. As the next step, the influence of LPS on the PmST1 activity was estimated by analyzing Michaelis-Menten plot. The enzyme activity of PmST1 was analyzed by measuring the concentration of CMP, which was a by-product after the transfer of the sialyl group of donor compounds to the acceptor compounds. From a Michaelis-Menten plot, the enzyme activity of the surface-displayed PmST1 and the maximum rate (V_max) of ClearColi were higher than those of wildtype E. coli (BL21). However, the K_M value, which represented the concentration of substrate to reach half the maximum rate (V_max), was similar for both enzymes. These results represented such a difference in enzyme activity was occurred from the interference of LPS on the mass transport of the donor and acceptor to PmST1 for the sialyl group transfer.

Autodisplay of the La/SSB protein on LPS-free E. coli for the diagnosis of Sjögren's syndrome

The objective of this study was to present an immunoassay for the diagnosis of Sjögren's syndrome based on the autodisplayed La/SSB protein on the outer membrane of intact E. coli (strain UT-5600) and LPS-free E. coli (ClearColi™). As the first step, an autodisplay vector (pCK002) was transfected into intact E. coli and LPS-free E. coli for comparison of efficiency of autdisplay of La/SSB. The maximal level of La/SSB expression was estimated to be similar for LPS-free E. coli and intact E. coli at different optimal induction periods. Intact E. coli was found to grow twofold faster than LPS-free E. coli, and the maximal level of expression for LPS-free E. coli was obtained with a longer induction period. When the zeta potential was measured, both intact E. coli and LPS-free E. coli showed negative values, and the autodisplay of negatively charged La/SSB protein (pI<7) on the outer membrane of intact E. coli and LPS-free E. coli resulted in a slight change in zeta potential values. E. coli with autodisplayed La/SSB protein was used for an immunoassay of anti-La/SSB antibodies for the diagnosis of Sjögren's syndrome. The surface of E. coli with the autodisplayed antigen was modified with rabbit serum and papain to prevent false positive signals because of nonspecific binding of unrelated antibodies from human serum. LPS-free E. coli with autodisplayed La/SSB protein yielded sensitivity and selectivity of 81.6% and 78.6%, respectively. The Bland-Altman test showed that the immunoassays based on LPS-free E. coli and intact E. coli with autodisplayed La/SSB protein were statistically equivalent to a clinical immunoassay for detection of anti-La/SSB antibodies (confidence coefficient 95%).

Large-scale purification and characterization of recombinant human stem cell factor in Escherichia coli

The pharmacological importance of recombinant human stem cell factor (rhSCF) has increased the demand to establish effective and large-scale production and purification processes. A good source of bioactive recombinant protein with capability of being scaled-up without losing activity has always been a challenge. The objectives of the study were the rapid and efficient pilot-scale expression and purification of rhSCF. The gene encoding stem cell factor (SCF) was cloned into pBV220 and transformed into Escherichia coli. The recombinant SCF was expressed and isolated using a procedure consisting of isolation of inclusion bodies (IBs), denaturation, and refolding followed by chromatographic steps toward purification. The yield of rhSCF reached 835.6 g/20 L, and the expression levels of rhSCF were about 33.9% of the total E. coli protein content. rhSCF was purified by isolation of IBs, denaturation, and refolding, followed by SP-Sepharose chromatography, Source 30 reversed-phase chromatography, and Q-Sepharose chromatography. This procedure was developed to isolate 5.5 g of rhSCF (99.5% purity) with specific activity at 0.96 × 10⁶  IU/mg, endotoxin levels of pyrogen at 1.0 EU/mg, and bacterial DNA at 10 ng/mg. Pilot-scale fermentations and purifications were set up for the production of rhSCF that can be upscaled for industry.

Harnessing the Profinity eXact™ System for Expression and Purification of Heterologous Proteins in E. coli

Highly purified recombinant proteins in large quantities are valuable material for biochemical and structural studies. To achieve this goal, versatile tools were developed to increase the expression of the recombinant proteins and to facilitate the purification process. Fusion tags are commonly used for enhancing expression and solubility and some can be used in the purification process. However, these tags may need to be removed by treatment with specific proteases in order to obtain the tag-free protein. The Profinity eXact™ system provides an alternative system for a fusion tag, enhancing expression and purification in one-step. Here we describe a set of new vectors in which the Profinity eXact™ tag, in addition to a 6× His-tag, with or without additional expression-enhancing sequences, could be used in the Profinity eXact™ system. We show that the solubility enhancing tags (Trx, GST, GB1) increase the yield of the purified tested protein compared to the vector containing only a His-tag upstream of the Profinity eXact™ fusion tag.

Recombinant pharmaceuticals from microbial cells: a 2015 update

Diabetes, growth or clotting disorders are among the spectrum of human diseases related to protein absence or malfunction. Since these pathologies cannot be yet regularly treated by gene therapy, the administration of functional proteins produced ex vivo is required. As both protein extraction from natural producers and chemical synthesis undergo inherent constraints that limit regular large-scale production, recombinant DNA technologies have rapidly become a choice for therapeutic protein production. The spectrum of organisms exploited as recombinant cell factories has expanded from the early predominating Escherichia coli to alternative bacteria, yeasts, insect cells and especially mammalian cells, which benefit from metabolic and protein processing pathways similar to those in human cells. Up to date, around 650 protein drugs have been worldwide approved, among which about 400 are obtained by recombinant technologies. Other 1300 recombinant pharmaceuticals are under development, with a clear tendency towards engineered versions with improved performance and new functionalities regarding the conventional, plain protein species. This trend is exemplified by the examination of the contemporary protein-based drugs developed for cancer treatment.