Escherichia coli expression and refolding of E/K-coil-tagged EGF generates fully bioactive EGF for diverse applications

Heterogeneous protein co-assemblies with tunable functional domain stoichiometry

In nature, the precise heterogeneous co-assembly of different protein domains gives rise to supramolecular machines that perform complex functions through the co-integrated activity of the individual protein subunits. A synthetic approach capable of mimicking this process would afford access to supramolecular machines with new or improved functional capabilities. Here we show that the distinct peptide strands of a heterotrimeric α-helical coiled-coil (i.e., peptides "A", "B", and "C") can be used as fusion tags for heterogeneous co-assembly of proteins into supramolecular structures with tunable subunit stoichiometry. In particular, we demonstrate that recombinant fusion of A with NanoLuc luciferase (NL-A), B with superfolder green fluorescent protein (sfGFP-B), and C with mRuby (mRuby-C) enables formation of ternary complexes capable of simultaneously emitting blue, green, and red light via sequential bioluminescence and fluorescence resonance energy transfer (BRET/FRET). Fusion of galectin-3 onto the C-terminus of NL-A, sfGFP-B, and mRuby-C endows the ternary complexes with lactose-binding affinity that can be tuned by varying the number of galectin-3 domains integrated into the complex from one to three, while maintaining BRET/FRET function. The modular nature of the fusion protein design, the precise control of domain stoichiometry, and the multiplicity afforded by the three-stranded coiled-coil scaffold provides access to a greater range of subunit combinations than what is possible with heterodimeric coiled-coils used previously. We envision that access to this expanded range of co-integrated protein domain diversity will be advantageous for future development of designer supramolecular machines for therapeutic, diagnostic, and biotechnology applications.

Molecular Pharming of the Recombinant Protein hEGF-hEGF Concatenated with Oleosin Using Transgenic Arabidopsis

We set out to assess the NIH/3T3 cell proliferation activity of Arabidopsis oil body-expressed recombinant oleosin–hEGF–hEGF protein. Normally, human epidermal growth factor (hEGF) is purified through complex process, however, oleosin fusion technology provides an inexpensive and scalable platform for its purification. Under a phaseolin promoter, we concatenated oleosin gene to double hEGF (hEGF–hEGF) with plant-preferred codons in the expression vectors and the construct was transformed into Arabidopsis thaliana (Arabidopsis). The transgenic Arabidopsis was validated by RT–PCR and the content of recombinant protein oleosin–hEGF–hEGF was quantified by western blot. Subsequently, the proliferation assay and transdermal absorption were determined by MTT method and immunohistochemical staining, respectively. First, the expression level of hEGF was recorded to be 14.83-ng/μL oil body and due to smaller size transgenic oil bodies expressing the recombinant oleosin–hEGF–hEGF, they were more skin permeable than those of control. Second, via the staining intensity of transgenic oil bodies was greater than EGF at all time points via immunohistochemical staining in transdermal absorption process. Lastly, activity assays of oil bodies expressed oleosin–hEGF–hEGF indicated that they stimulated the NIH/3T3 cell proliferation activity. Our results revealed oil-body-expressed oleosin–hEGF–hEGF was potential new material having implications in the field of medicine.

Bioavailability of immobilized epidermal growth factor: Covalent versus noncovalent grafting

In an effort to rationalize and optimize an antiapoptotic coating combining chondroitin sulfate (CS) and epidermal growth factor (EGF) for vascular applications, the authors here report the comparison of two grafting strategies aiming to display EGF in an oriented fashion on CS. For that purpose, the authors produced, purified, and characterized a chimeric protein corresponding to EGF that was N-terminally fused to a cysteine and a coil peptide. The chimera was covalently immobilized via its free thiol group or captured via coiled-coil interactions at the surface of a biosensor or on a chondroitin sulfate coating in multiwell plates, mimicking the coating that was previously developed by them for stent-graft surfaces. The interactions of grafted EGF with the soluble domain of its receptor or the impact of grafted EGF upon vascular smooth muscle survival in proapoptotic conditions indicated that the coiled-coil based tethering was the best approach to display EGF. These results, combined to direct enzyme-linked immunosorbent assay measurements, indicated that the coiled-coil tethering approach allowed increasing the amount of bioavailable EGF when compared to covalent coupling, rather than the total amount of grafted EGF, while using much lower concentrations of tagged EGF during incubation.

Soluble expression, purification and functional characterization of a coil peptide composed of a positively charged and hydrophobic motif

A de novo heterodimeric coiled-coil system formed by the association of two synthetic peptides, the Ecoil and Kcoil, has been previously designed and proven to be an excellent and versatile tool for various biotechnology applications. However, based on the challenges encountered during its chemical synthesis, the Kcoil peptide has been designated as a "difficult peptide". In this study, we explore the expression of the Kcoil peptide by a bacterial system as well as its subsequent purification. The maximum expression level was observed when the peptide was fused to thioredoxin and the optimized purification process consisted of three chromatographic steps: immobilized-metal affinity chromatography followed by cation-exchange chromatography and, finally, a reverse-phase high-performance liquid chromatography. This entire process led to a final volumetric production yield of 1.5 mg of pure Kcoil peptide per liter of bacterial culture, which represents a significant step towards the cost-effective production and application of coiled-coil motifs. Our results thus demonstrate for the first time that bacterial production is a viable alternative to the chemical synthesis of de novo designed coil peptides.

High-yield reactivation of anionic tobacco peroxidase overexpressed in Escherichia coli

Anionic tobacco peroxidase (TOP) is extremely active in chemiluminescence reaction of luminol oxidation without addition of enhancers and more stable than horseradish peroxidase under antibody conjugation conditions. In addition, recombinant TOP (rTOP) produced in Escherichia coli is known to be a perfect direct electron transfer catalyst on electrodes of various origin. These features make the task of development of a high-yield reactivation protocol for rTOP practically important. Previous attempts to reactivate the enzyme from E. coli inclusion bodies were successful, but the reported reactivation yield was only 14%. In this work, we thoroughly screened the refolding conditions for dilution protocol and compared it with gel-filtration chromatography. The impressive reactivation yield in the dilution protocol (85%) was achieved for 8 μg/mL solubilized rTOP protein and the refolding medium containing 0.3 mM oxidized glutathione, 0.05 mM dithiothreitol, 5 mM CaCl2, 5% glycerol in 50 mM Tris-HCl buffer, pH 9.6, with 1 μM hemin added at the 24th hour of incubation. A practically important discovery was a 30-40% increase in the reactivation yield upon delayed addition of hemin. The reactivation yield achieved is one of the highest reported in the literature on protein refolding by dilution. The final yield of purified active non-glycosylated rTOP was ca. 60 mg per L of E. coli culture, close to the yield reported before for tomato and tobacco plants overexpressing glycosylated TOP (60 mg/kg biomass) and much higher than for the previously reported refolding protocol (2.6 mg per L of E. coli culture).

High-level expression and purification of soluble bioactive recombinant human heparin-binding epidermal growth factor in Escherichia coli

Heparin-binding epidermal growth factor (HB-EGF) is a member of highly conserved superfamily of proteins that has potential mitogenic activity and stimulates differentiation and migration of various cell types. Since HB-EGF has three intra-molecular disulfide bonds, a high expression pattern of active HB-EGF in an E. coli expression system was not successfully established. The aim of this study was to increase production of soluble bioactive recombinant human HB-EGF in E. coli by modifying growth conditions and codon optimization. The open reading frame codons of human HB-EGF were optimized to achieve high level expression in E. coli. The optimized codon was amplified, cloned into plasmid pET-32a, and transformed into E. coli BL21 for further expression. The cultivation parameters (temperature and inducer) were optimized to produce a high yield of soluble HB-EGF. The fusion protein was purified by Nickel-nitrilotriacetic acid (Ni-NTA) affinity chromatography. Amethylthiazole tetrazolium assay was used to evaluate the bioactivity of the produced recombinant protein. After codon optimization, the codon adaptation index (CAI) was increased from 0.255 in native gene to 0.829 using the optimized sequence. By lowering the temperature to 22°C and the inducer to 0.4 μM, we obtained 35% soluble expression of recombinant and biologically active human HB-EGF. Our data demonstrate that codon optimization increases the yield of HB-EGF in an E. coli expression system. Furthermore, the chosen modifications in cell culturing increase the solubility of recombinant human HB-EGF.

claMP Tag: a versatile inline metal-binding platform based on the metal abstraction peptide

Molecularly targeted research and diagnostic tools are essential to advancing understanding and detection of many diseases. Metals often impart the desired functionality to these tools, and conjugation of high-affinity chelators to proteins is carried out to enable targeted delivery of the metal. This approach has been much more effective with large lanthanide series metals than smaller transition metals. Because chemical conjugation requires additional processing and purification steps and yields a heterogeneous mixture of products, inline incorporation of a peptide tag capable of metal binding is a highly preferable alternative. Development of a transition metal binding tag would provide opportunity to greatly expand metal-based analyses. The metal abstraction peptide (MAP) sequence was genetically engineered into recombinant protein to generate the claMP Tag. The effects of this tag on recombinant epidermal growth factor (EGF) protein expression, disulfide bond formation, tertiary structural integrity, and transition metal incorporation using nickel were examined to confirm the viability of utilizing the MAP sequence to generate linker-less metal conjugates.

Short peptide tag for covalent protein labeling based on coiled coils

To label proteins covalently, one faces a trade-off between labeling a protein specifically and using a small tag. Often one must compromise one parameter for the other or use additional components, such as an enzyme, to satisfy both requirements. Here, we report a new reaction that covalently labels proteins by using engineered coiled-coil peptides. Harnessing the concept of "proximity-induced reactivity", the 21-amino-acid three-heptad peptides CCE/CCK were modified with a nucleophilic cysteine and an α-chloroacetyl group at selected positions. When pairs of coiled coils associated, an irreversible covalent bond spontaneously formed between the peptides. The specificity of the cross-linking reaction was characterized, the probes were improved by making them bivalent, and the system was used to label a protein in vitro and receptors on the surface of mammalian cells.

New ELISA approach based on coiled-coil interactions

The de novo designed heterodimeric E/K coiled-coil system has been previously demonstrated to be an excellent capture/dimerization system applicable to various needs in both biotechnology and pharmaceutical fields. Those include controlled protein dimerization, capture, purification and Western-blot detection. We here report the development of a new generation of ELISA test based on coiled-coil interactions for the direct quantitation of coil-tagged epidermal growth factor (EGF). The new approach was evaluated for its specificity, plate storability and reusability as well as for convenience when compared to commercially available systems. Our results show a similar affinity/sensitivity to standard capturing antibody-based ELISA systems and an improved affinity/sensitivity when compared to the commercially available Ni-NTA capture system. The E/K coiled-coil ELISA system was validated with respect to recovery, intra- and inter-assay variations. The practical working range was estimated to be between 5.2 and 34,000 pM. Furthermore, the storability and reusability of the plates was greater than the two aforementioned systems, suggesting that the E/K coiled-coil system is a good alternative to traditional tags such as poly-histidine for the development of ELISA tests aiming at quantitating coil-tagged proteins.

An efficient method for expression in Escherichia coli and purification of the extracellular ligand binding domain of the human TGFbeta type II receptor

TGFbeta signaling is initiated by binding of growth factor ligand to two related single-pass transmembrane receptor serine/threonine kinases, known as the TGFbeta type I (TbetaRI) and type II (TbetaRII-ED) receptors. TbetaRII-ED is essential for all TGFbeta-induced signals. The DNA sequence encoding the extracellular domain of human TbetaRII-ED (TbetaRII-ED, residues 4-136) was synthesized from 20 oligonucleotides by polymerase chain reaction and cloned into plasmid pET-32a downstream to the gene of fusion partner thioredoxin immediately after the DNA sequence encoding enteropeptidase recognition site. High level expression ( approximately 1 gL(-1)) of thioredoxin/TbetaRII-ED fusion was achieved in Escherichia coli BL21(DE3) strain mainly in soluble form. The soluble thioredoxin/TbetaRII-ED fusion has been purified and refolded on Ni-NTA agarose. After cleavage of purified thioredoxin/TbetaRII-ED fusion by recombinant human enteropeptidase light chain (L-HEP) the target protein of TbetaRII-ED was separated from thioredoxin on Ni-NTA agarose. Fourteen milligrams of highly purified TbetaRII-ED without N- or C-terminal tags was yielded from 100mL cell culture. The purified preparation of TbetaRII-ED was highly homogenous, as shown by SDS-PAGE with silver staining, HPLC and mass spectroscopy analysis. The binding of TbetaRII-ED purified from E. coli to TGFbeta1 was shown to be comparable to commercial material purified from NSO cells. Recombinant TbetaRII-ED could be employed as an antagonist of TGFbeta1 and TGFbeta3 in vitro and in vivo as well as for therapy of fibrotic disorders and some types of cancer.

Protein detection by Western blot via coiled-coil interactions

We propose an approach for the detection of proteins by Western blot that takes advantage of the high-affinity interaction occurring between two de novo designed peptides, the E and K coils. As a model system, K coil-tagged epidermal growth factor (EGF) was revealed with secreted alkaline phosphatase (SeAP) tagged with E coil (SeAP-Ecoil) as well as with biotinylated E coil. In that respect, we first produced purified SeAP-Ecoil and verified its ability to interact with K coil peptides by surface plasmon resonance biosensing. We demonstrated that protein detection with Ecoil-biotin was more specific than with SeAP-Ecoil. We then showed that our approach is as sensitive as conventional detection strategies relying on nickel-nitrilotriacetic acid-horseradish peroxidase (Ni-NTA-HRP), anti-His-HRP, or anti-EGF. Altogether, our results indicate that the E/K coiled-coil system is a good alternative for protein detection by Western blot.