Prokaryotic soluble expression and purification of bioactive human fibroblast growth factor 21 using maltose-binding protein

Recombinant Porcine FGF1 Promotes Muscle Stem Cell Proliferation and Mitochondrial Function for Cultured Meat Production

Cultured meat is an emerging technology with the potential to meet future protein demands while addressing the challenges associated with traditional livestock farming. The production of cultured meat requires efficient, animal component-free in vitro systems for muscle stem cell (MuSC) expansion. Fibroblast growth factor 1 (FGF1) is a critical growth factor that regulates the MuSC function. In this study, we established an efficient method for the soluble expression and purification of recombinant porcine FGF1 (rpFGF1) in Escherichia coli, achieving a yield of 48 mg of purified protein per liter of culture. Treatment with rpFGF1 significantly enhanced the proliferation of porcine MuSC under serum-free conditions. Furthermore, rpFGF1 induced mitochondrial fission and mitophagy by activating the ERK-dependent phosphorylation of DRP1 at Ser616, resulting in improved mitochondrial function and proliferation capacity in porcine MuSC. These findings highlight the potential of rpFGF1 in the development of serum-free media for scalable and sustainable cultured meat production.

Self-assembly systems to troubleshoot metabolic engineering challenges

Enzyme self-assembly is a technology in which enzyme units can aggregate into ordered macromolecules, assisted by scaffolds. In metabolic engineering, self-assembly strategies have been explored for aggregating multiple enzymes in the same pathway to improve sequential catalytic efficiency, which in turn enables high-level production. The performance of the scaffolds is critical to the formation of an efficient and stable assembly system. This review comprehensively analyzes these scaffolds by exploring how they assemble, and it illustrates how to apply self-assembly strategies for different modules in metabolic engineering. Functional modifications to scaffolds will further promote efficient strategies for production.

Tagging Recombinant Proteins to Enhance Solubility and Aid Purification

Protein fusion technology has had a major impact on the efficient production and purification of individual recombinant proteins. The use of genetically engineered affinity and solubility-enhancing polypeptide "tags" has a long history, and there is a considerable repertoire of these that can be used to address issues related to the expression, stability, solubility, folding, and purification of their fusion partner. In the case of large-scale proteomic studies, the development of purification procedures tailored to individual proteins is not practicable, and affinity tags have become indispensable tools for structural and functional proteomic initiatives that involve the expression of many proteins in parallel. In this chapter, the rationale and applications of a range of established and more recently developed solubility-enhancing and affinity tags is described.

In vivo enzymatic digestion of HRV 3C protease cleavage sites-containing proteins produced in a silkworm-baculovirus expression system

Baculovirus expression vector system (BEVS) has been recognized as a potent protein expression system in engineering valuable enzymes and vaccines. Various fusion tags facilitate protein purification, leaving the potential risk to influence the target protein's biological activity negatively. It is of great interest to consider removing the additional tags using site-specific proteases, such as human rhinoviruses (HRV) 3C protease. The current study validated the cleavage activity of 3C protease in Escherichia coli and silkworm-BEVS systems by mixing the cell or fat body lysates of 3C protein and 3C site containing target protein in vitro. Further verification has been performed in the fat body lysate from co-expression of both constructs, showing remarkable cleavage efficiency in vivo silkworm larvae. We also achieved the glutathione-S-transferase (GST) tag-cleaved product of the VP15 protein from the White spot syndrome virus after purification, suggesting that we successfully established a coinfection-based recognition-and-reaction BEVS platform for the tag-free protein engineering.

In-Depth Characterization of a Re-Engineered Cholera Toxin Manufacturing Process Using Growth-Decoupled Production in Escherichia coli

Non-toxic derivatives of the cholera toxin are extensively used in neuroscience, as neuronal tracers to reveal the location of cells in the central nervous system. They are, also, being developed as vaccine components and drug-delivery vehicles. Production of cholera-toxin derivatives is often non-reproducible; the quality and quantity require extensive fine-tuning to produce them in lab-scale settings. In our studies, we seek a resolution to this problem, by expanding the molecular toolbox of the Escherichia coli expression system with suitable production, purification, and offline analytics, to critically assess the quality of a probe or drug delivery, based on a non-toxic derivative of the cholera toxin. We present a re-engineered Cholera Toxin Complex (rCTC), wherein its toxic A1 domain was replaced with Maltose Binding Protein (MBP), as a model for an rCTC-based targeted-delivery vehicle. Here, we were able to improve the rCTC production by 11-fold (168 mg/L vs. 15 mg/L), in comparison to a host/vector combination that has been previously used (BL21(DE3) pTRBAB5-G1S). This 11-fold increase in the rCTC production capability was achieved by (1) substantial vector backbone modifications, (2) using Escherichia coli strains capable of growth-decoupling (V strains), (3) implementing a well-tuned fed-batch production protocol at a 1 L scale, and (4) testing the stability of the purified product. By an in-depth characterization of the production process, we revealed that secretion of rCTC across the E. coli Outer Membrane (OM) is processed by the Type II secretion-system general secretory pathway (gsp-operon) and that cholera toxin B-pentamerization is, likely, the rate-limiting step in complex formation. Upon successful manufacturing, we have validated the biological activity of rCTC, by measuring its binding affinity to its carbohydrate receptor GM1 oligosaccharide (Kd = 40 nM), or binding to Jurkat cells (93 pM) and delivering the cargo (MBP) in a retrograde fashion to the cell.

Redesigned pMAL expression vector for easy and fast purification of active native antimicrobial peptides

AIMS

The aim of this study was to construct the improved pMAL expression vector in order to increase the efficacy of small native peptides purification and their clear-cut separation from MBP tag. The modifications we introduced can be applied to many expression vectors.

METHODS AND RESULTS

To improve the pMAL expression vector we introduced the His₆ tag and the enterokinase cleavage site (Ek) downstream from the MBP tag and Xa cleavage site on the original vector. For cloning of a desired peptide DNA, the enterokinase site contains a unique BsaBI restriction site adjacent to the original multi-cloning-site. This redesigned pMAL vector was optimized for the purification of cytoplasmic (pMALc5HisEk) and periplasmic (pMALp5HisEk) peptides. The purification of native and active peptide (P) was obtained following two-step affinity chromatography. In the first step the entire MBP-His₆ -Ek-P fusion protein is purified using the Ni-NTA agarose column. This fusion protein was cleaved with active His₆ tagged enterokinase. In the second step, the further purification was performed by column containing the mixture of amylose and Ni-NTA agarose resins. This removes both the MBP-His₆ and His₆ -enterokinase leaving pure native protein in solution. These new vectors and the two-step purification protocol was successfully applied in purification of active native small antimicrobial peptides (AMPs), lactococcin A and human β-defensin.

CONCLUSIONS

We constructed the improved pMAL expression vectors and established the pipeline and optimal conditions for their use in efficient purification of large amounts of active native small peptides.

SIGNIFICANCE AND IMPACT OF THE STUDY

Choice of expression vector impacts on the efficiency of expression and purification of desired proteins. The idea of redesigning pMAL vector was driven by need for rapid purification of larger amounts of active native AMPs. This newly improved pMAL vector, the cloning strategy, expression conditions and two-step purification protocol represent a unique simple approach which can be applied in every laboratory.

Refolding of bioactive human epidermal growth factor from E. coli BL21(DE3) inclusion bodies & evaluations on its in vitro & in vivo bioactivity

Human epidermal growth factor (hEGF) is a mitogenic protein widely used in pharmaceutical and cosmetic industries, thus recombinant DNA technology has been applied to meet the high demand for hEGF. The overexpression of recombinant protein in E. coli often leads to the formation of inclusion bodies (IBs). Mild solubilisation preserves the native secondary protein structure in IBs, thereby the high recovery of active protein from IBs. The redox system also plays a pivotal role in the formation of disulphide bonds during refolding of disulphide bond-containing protein. This study aimed to recover hEGF from bacterial IBs through freeze-thawing solubilisation and glutathione-based oxidative refolding. CBD-Ssp DnaB-hEGF fusion protein was expressed as IBs in E. coli, washed with Triton X-100 and urea to remove most protein contaminants, then the solubilised fusion protein was obtained by freeze-thawing with the addition of 2 M urea. The solubilised protein was subsequently refolded by intein cleavage via a glutathione-based redox system. The refolded hEGF demonstrated heat-resistant properties, interacted with specific antibodies on ELISA, stimulated keratinocyte proliferation and possessed significant in vivo wound healing properties on the 8th day, confirming that hEGF was correctly folded. In summary, the protocol described is suitable for the recovery of refolded hEGF from bacterial IBs by mild solubilisation and oxidative refolding.

Biofoundry-assisted expression and characterization of plant proteins

Many goals in synthetic biology, including the elucidation and refactoring of biosynthetic pathways and the engineering of regulatory circuits and networks, require knowledge of protein function. In plants, the prevalence of large gene families means it can be particularly challenging to link specific functions to individual proteins. However, protein characterization has remained a technical bottleneck, often requiring significant effort to optimize expression and purification protocols. To leverage the ability of biofoundries to accelerate design-built-test-learn cycles, we present a workflow for automated DNA assembly and cell-free expression of plant proteins that accelerates optimization and enables rapid screening of enzyme activity. First, we developed a phytobrick-compatible Golden Gate DNA assembly toolbox containing plasmid acceptors for cell-free expression using Escherichia coli or wheat germ lysates as well as a set of N- and C-terminal tag parts for detection, purification and improved expression/folding. We next optimized automated assembly of miniaturized cell-free reactions using an acoustic liquid handling platform and then compared tag configurations to identify those that increase expression. We additionally developed a luciferase-based system for rapid quantification that requires a minimal 11-amino acid tag and demonstrate facile removal of tags following synthesis. Finally, we show that several functional assays can be performed with cell-free protein synthesis reactions without the need for protein purification. Together, the combination of automated assembly of DNA parts and cell-free expression reactions should significantly increase the throughput of experiments to test and understand plant protein function and enable the direct reuse of DNA parts in downstream plant engineering workflows.

Soluble Cytoplasmic Expression and Purification of Immunotoxin HER2(scFv)-PE24B as a Maltose Binding Protein Fusion

Human epidermal growth factor receptor 2 (HER-2) is overexpressed in many malignant tumors. The anti-HER2 antibody trastuzumab has been approved for treating HER2-positive early and metastatic breast cancers. Pseudomonas exotoxin A (PE), a bacterial toxin of Pseudomonas aeruginosa, consists of an A-domain with enzymatic activity and a B-domain with cell binding activity. Recombinant immunotoxins comprising the HER2(scFv) single-chain Fv from trastuzumab and the PE24B catalytic fragment of PE display promising cytotoxic effects, but immunotoxins are typically insoluble when expressed in the cytoplasm of Escherichia coli, and thus they require solubilization and refolding. Herein, a recombinant immunotoxin gene was fused with maltose binding protein (MBP) and overexpressed in a soluble form in E. coli. Removal of the MBP yielded stable HER2(scFv)-PE24B at 91% purity; 0.25 mg of pure HER2(scFv)-PE24B was obtained from a 500 mL flask culture. Purified HER2(scFv)-PE24B was tested against four breast cancer cell lines differing in their surface HER2 level. The immunotoxin showed stronger cytotoxicity than HER2(scFv) or PE24B alone. The IC50 values for HER2(scFv)-PE24B were 28.1 ± 2.5 pM (n = 9) and 19 ± 1.4 pM (n = 9) for high HER2-positive cell lines SKBR3 and BT-474, respectively, but its cytotoxicity was lower against MDA-MB-231 and MCF7. Thus, fusion with MBP can facilitate the soluble expression and purification of scFv immunotoxins.

Soluble Prokaryotic Overexpression and Purification of Human GM-CSF Using the Protein Disulfide Isomerase b'a' Domain

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a member of the colony-stimulating factor (CSF) family, which functions to enhance the proliferation and differentiation of hematopoietic stem cells and other hematopoietic lineages such as neutrophils, dendritic cells, or macrophages. These proteins have thus generated considerable interest in clinical therapy research. A current obstacle to the prokaryotic production of human GM-CSF (hGM-CSF) is its low solubility when overexpressed and subsequent complex refolding processes. In our present study, the solubility of hGM-CSF was examined when combined with three N-terminal fusion tags in five E. coli strains at three different expression temperatures. In the five E. coli strains BL21 (DE3), ClearColi BL21 (DE3), LOBSTR, SHuffle T7 and Origami2 (DE3), the hexahistidine-tagged hGM-CSF showed the best expression but was insoluble in all cases at each examined temperature. Tagging with the maltose-binding protein (MBP) and the b'a' domain of protein disulfide isomerase (PDIb'a') greatly improved the soluble overexpression of hGM-CSF at 30 °C and 18 °C. The solubility was not improved using the Origami2 (DE3) and SHuffle T7 strains that have been engineered for disulfide bond formation. Two conventional chromatographic steps were used to purify hGM-CSF from the overexpressed PDIb'a'-hGM-CSF produced in ClearColi BL21 (DE3). In the experiment, 0.65 mg of hGM-CSF was isolated from a 0.5 L flask culture of these E. coli and showed a 98% purity by SDS-PAGE analysis and silver staining. The bioactivity of this purified hGM-CSF was measured at an EC₅₀ of 16.4 ± 2 pM by a CCK8 assay in TF-1 human erythroleukemia cells.

Effective production of human growth factors in Escherichia coli by fusing with small protein 6HFh8

Background

Growth factors (GFs) are signaling proteins that affect cellular processes such as growth, proliferation, and differentiation. GFs are used as cosmeceuticals, exerting anti-wrinkle, anti-aging, and whitening effects, and also as pharmaceuticals to treat wounds, growth failure, and oral mucositis. However, in mammalian and bacterial cells, low productivity and expression in inclusion bodies, respectively, of GFs does not satisfy the consumer demand. Here, we aimed to develop a bacterial expression system that produces high yields of soluble GFs that can be purified in their native forms.

Results

We present Fh8, an 8-kDa peptide from Fasciola hepatica with an N-terminal hexa-histidine (6HFh8), as a fusion partner for enhanced human GF production in recombinant Escherichia coli. The fusion partner harboring a tobacco etch virus (TEV) protease cleavage site was fused to the N-terminus of 10 human GFs: acidic and basic fibroblast growth factors (aFGF and bFGF, respectively), epidermal growth factor (EGF), human growth hormone (hGH), insulin-like growth factor 1 (IGF-1), vascular endothelial growth factor 165 (VEGF165), keratinocyte growth factor 1 (KGF-1), placental growth factor (PGF), stem cell factor (SCF), and tissue inhibitor of metalloproteinase 1 (TIMP-1). The fusion proteins were expressed in E. coli under the control of T7 promoter at three temperatures (25 °C, 30 °C, and 37 °C). All individual fusion proteins, except for SCF and TIMP-1, were successfully overexpressed in cytoplasmic soluble form at more than one temperature. Further, the original aFGF, IGF-1, EGF, and VEGF165 proteins were cleaved from the fusion partner by TEV protease. Five-liter fed-batch fermentation approaches for the 6HFh8-aFGF (lacking disulfide bonds) and 6HFh8-VEGF165 (a cysteine-rich protein) were devised to obtain the target protein at concentrations of 9.7 g/l and 3.4 g/l, respectively. The two GFs were successfully highly purified (> 99% purity). Furthermore, they exerted similar cell proliferative effects as those of their commercial equivalents.

Conclusions

We demonstrated that 6HFh8-GF fusion proteins could be overexpressed on a g/l scale in the cytoplasm of E. coli, with the GFs subsequently highly purified and maintaining their biological activity. Hence, the small protein 6HFh8 can be used for efficient mass-production of various GFs.

Bacterial overexpression and purification of soluble recombinant human serum albumin using maltose-binding protein and protein disulphide isomerase

Human serum albumin (HSA), the most abundant serum protein in healthy humans, plays important roles in many physiological processes and has wide clinical and research applications. Despite several efforts to obtain recombinant HSA (rHSA) from bacterial and eukaryotic expression systems, a low-cost and high-yield method for rHSA production is not available. The large molecular weight and high disulphide content hamper the expression and production of rHSA using bacterial hosts. Hence, a strategy that uses a fusion technique and engineered Escherichia coli strains was employed to improve the expression of soluble rHSA in the bacterial cytoplasm. The solubilities of the b'a' domain of human protein disulphide isomerase (PDIb'a')- and maltose-binding protein (MBP)-tagged rHSA expressed in Origami 2 at 18 °C were notably increased by up to 90.1% and 96%, respectively. A simple and efficient protocol for rHSA purification was established and approximately 9.46 mg rHSA was successfully obtained from a 500-mL culture at 97% purity. However, rHSA was mostly obtained in soluble oligomeric form. By introducing a simple refolding and size-exclusion chromatography step, monomeric rHSA was obtained at 34% yield. Native polyacrylamide gel electrophoresis confirmed the similarity in the molecular weights between E. coli-derived monomeric rHSA and commercial monomeric HSA.

Prokaryotic soluble overexpression and purification of oncostatin M using a fusion approach and genetically engineered E. coli strains

Human Oncostatin M (OSM), initially discovered as a tumour inhibitory factor secreted from U-937 cells, is a gp130 (IL-6/LIF) cytokine family member that exhibits pleiotropic effects in inflammation, haematopoiesis, skeletal tissue alteration, liver regeneration, cardiovascular and metabolic diseases. Cytoplasmic expression of OSM in Escherichia coli results in inclusion bodies, and complex solubilisation, refolding and purification is required to prepare bioactive protein. Herein, eight N-terminal fusion variants of OSM with hexahistidine (His6) tag and seven solubility-enhancing tags, including thioredoxin (Trx), small ubiquitin-related modifier (Sumo), glutathione S-transferase (GST), maltose-binding protein (MBP), N-utilisation substance protein A (Nusa), human protein disulphide isomerase (PDI) and the b‘a’ domain of PDI (PDIb‘a’), were tested for soluble OSM expression in E. coli. The His6-OSM plasmid was also introduced into genetically engineered Origami 2 and SHuffle strains to test expression of the protein. At 18 °C, MBP-tagged OSM was highly expressed and solubility was dramatically enhanced. In addition, His6-OSM was more highly expressed and soluble in Origami 2 and SHuffle strains than in BL21(DE3). MBP-OSM and His6-OSM were purified more than 95% with yields of 11.02 mg and 3.27 mg from a 500 mL culture. Protein identity was confirmed by mass spectroscopy, and bioactivity was demonstrated by in vitro inhibition of Th17 cell differentiation.

Fibroblast Growth Factor-21 Controls Dietary Protein Intake in Male Mice

Whereas carbohydrates and lipids are stored as glycogen and fat, there is no analogous inert storage form of protein. Therefore, continuous adjustments in feeding behavior are needed to match amino acid supply to ongoing physiologic need. Neuroendocrine mechanisms facilitating this behavioral control of protein and amino acid homeostasis remain unclear. The hepatokine fibroblast growth factor-21 (FGF21) is well positioned for such a role, as it is robustly secreted in response to protein and/or amino acid deficit. In this study, we tested the hypothesis that FGF21 feeds back at its receptors in the nervous system to shift macronutrient selection toward protein. In a series of behavioral tests, we isolated the effect of FGF21 to influence consumption of protein, fat, and carbohydrate in male mice. First, we used a three-choice pure macronutrient-diet paradigm. In response to FGF21, mice increased consumption of protein while reducing carbohydrate intake, with no effect on fat intake. Next, to determine whether protein or carbohydrate was the primary-regulated nutrient, we used a sequence of two-choice experiments to isolate the effect of FGF21 on preference for each macronutrient. Sweetness was well controlled by holding sucrose constant across the diets. Under these conditions, FGF21 increased protein intake, and this was offset by reducing the consumption of either carbohydrate or fat. When protein was held constant, FGF21 had no effect on macronutrient intake. Lastly, the effect of FGF21 to increase protein intake required the presence of its co-receptor, β-klotho, in neurons. Taken together, these findings point to a novel liver→nervous system pathway underlying the regulation of dietary protein intake via FGF21.

A simplified method to remove fusion tags from a xylanase of Bacillus sp. HBP8 with HRV 3C protease

Human rhinovirus 3C protease (HRV 3C protease) is commonly used as a tool to remove fusion tags from recombinant proteins in gene engineering due to its distinguished specificity and high activity at low temperature. This paper is aimed to simplify the strategy of removing epitope tags from target proteins with HRV 3C protease. Fusion proteins composed of a xylanase from Bacillus sp. HBP8 (xylHB) and double tags (MBP/Nus and 6×His, with an HRV 3C protease recognition site between them) were applied as substrates. To perform the cleavage and purification, strains expressing HRV 3C protease and the substrates were mixed before (co-fermentation method) or after (post-fermentation method) inducing with IPTG, followed by cell disruption and incubation at 4℃, overnight for cleavage. The soluble cytoplasmic fraction was added to Ni-NTA resin to recover the cleaved target protein. Because the process was carried out in the cell lysate, it was named as cell lysate purification system based on HRV 3C protease (CLP3C). Our data indicated small number of cells expressing HRV 3C protease was enough to remove the fusion tags efficiently with both co-fermentation and post-fermentation methods. More importantly, the tags were cleaved precisely with no obvious non-specific degradation to the target protein. Hence, active xylanase was recovered easily with this strategy.

Myomaker and Myomerger Work Independently to Control Distinct Steps of Membrane Remodeling during Myoblast Fusion

Classic mechanisms for membrane fusion involve transmembrane proteins that assemble into complexes and dynamically alter their conformation to bend membranes, leading to mixing of membrane lipids (hemifusion) and fusion pore formation. Myomaker and Myomerger govern myoblast fusion and muscle formation but are structurally divergent from traditional fusogenic proteins. Here, we show that Myomaker and Myomerger independently mediate distinct steps in the fusion pathway, where Myomaker is involved in membrane hemifusion and Myomerger is necessary for fusion pore formation. Mechanistically, we demonstrate that Myomerger is required on the cell surface where its ectodomains stress membranes. Moreover, we show that Myomerger drives fusion completion in a heterologous system independent of Myomaker and that a Myomaker-Myomerger physical interaction is not required for function. Collectively, our data identify a stepwise cell fusion mechanism in myoblasts where different proteins are delegated to perform unique membrane functions essential for membrane coalescence.

Codon optimization significantly enhanced the expression of human 37-kDa iLRP in Escherichia coli

37-kDa immature laminin receptor protein (iLRP), the precursor of 67-kDa laminin receptor protein (LRP), is overexpressed on the surface of most cancer cells and recognized as a universal tumor antigen. The role makes it a potential target for cancer immunotherapy, which has been well-studied. Our study aimed to produce high quality of human iLRP in bacteria so that the needs in research of its clinical application could be met. The powerful system for heterologous protein expression, pET system was used. Two types of DNA sequences encoding the same amino acid sequences were separately cloned into the vector pET30a(+). One of the resulting vectors includes the wild-type iLRP, and other one includes the codon-optimized iLRP. The expression by both genes was then compared in Escherichia coli BL21(DE3). Our results revealed that the performance of codon optimization was crucial for the expression of human iLRP in Escherichia coli. The yield was significantly enhanced up to 300 mg/L of bacterial culture by this approach.