Production of Extracellular Matrix Proteins in the Cytoplasm of E. coli: Making Giants in Tiny Factories

Escherichia coli Cytoplasmic Expression of Disulfide-Bonded Proteins: Side-by-Side Comparison between Two Competing Strategies

The production of disulfide bond-containing recombinant proteins in Escherichia coli has traditionally been done by either refolding from inclusion bodies or by targeting the protein to the periplasm. However, both approaches have limitations. Two broad strategies were developed to allow the production of proteins with disulfide bonds in the cytoplasm of E. coli: i) engineered strains with deletions in the disulfide reduction pathways, e.g. SHuffle, and ii) the co-expression of oxidative folding catalysts, e.g. CyDisCo. However, to our knowledge, the relative effectiveness of these strategies has not been properly evaluated. Here, we systematically compare the purified yields of 14 different proteins of interest (POI) that contain disulfide bonds in their native state when expressed in both systems. We also compared the effects of different background strains, commonly used promoters, and two media types: defined and rich autoinduction. In rich autoinduction media, POI which can be produced in a soluble (non-native) state without a system for disulfide bond formation were produced in higher purified yields from SHuffle, whereas all other proteins were produced in higher purified yields using CyDisCo. In chemically defined media, purified yields were at least 10x higher in all cases using CyDisCo. In addition, the quality of the three POI tested was superior when produced using CyDisCo.

Essential factors, advanced strategies, challenges, and approaches involved for efficient expression of recombinant proteins in Escherichia coli

Producing recombinant proteins is a major accomplishment of biotechnology in the past century. Heterologous hosts, either eukaryotic or prokaryotic, are used for the production of these proteins. The utilization of microbial host systems continues to dominate as the most efficient and affordable method for biotherapeutics and food industry productions. Hence, it is crucial to analyze the limitations and advantages of microbial hosts to enhance the efficient production of recombinant proteins on a large scale. E. coli is widely used as a host for the production of recombinant proteins. Researchers have identified certain obstacles with this host, and given the growing demand for recombinant protein production, there is an immediate requirement to enhance this host. The following review discusses the elements contributing to the manifestation of recombinant protein. Subsequently, it sheds light on innovative approaches aimed at improving the expression of recombinant protein. Lastly, it delves into the obstacles and optimization methods associated with translation, mentioning both cis-optimization and trans-optimization, producing soluble recombinant protein, and engineering the metal ion transportation. In this context, a comprehensive description of the distinct features will be provided, and this knowledge could potentially enhance the expression of recombinant proteins in E. coli.

Efficient Production of Fc Fusion Proteins in the Cytoplasm of Escherichia coli: Dissecting and Mitigating Redox Heterogeneity

Cost-effective production of therapeutic proteins in microbial hosts is an indispensable tool towards accessible healthcare. Many of these heterologously expressed proteins, including all antibody formats, require disulfide bond formation to attain their native and functional state. A system for catalyzed disulfide bond formation (CyDisCo) has been developed allowing efficient production of recombinant proteins in the cytoplasm of one of the most used microbial expression systems, Escherichia coli. Here, we report high-yield production (up to 230 mg/L from 3 mL cultures) of in-demand therapeutics such as IgG₁-based Fc fusion proteins in the E. coli cytoplasm. However, the production of this drug class using the CyDisCo system faces bottlenecks related to redox heterogeneity during oxidative folding. Our investigations identified and addressed one of the major causes of redox heterogeneity during CyDisCo-based production of Fc fusion proteins, i.e., disulfide bond formation in the IgG₁ C_H3 domain. Here, we communicate that mutating the cysteines in the C_H3 domain of target Fc fusion proteins allows their production in a homogeneous redox state in the cytoplasm of E. coli without compromising on yields and thermal stability.

Enhanced Production of ECM Proteins for Pharmaceutical Applications Using Mammalian Cells and Sodium Heparin Supplementation

The yields of soluble ECM proteins recombinantly produced with mammalian cells can be significantly enhanced by exploiting the stabilizing properties of heparin. Here, we propose a simple and straightforward scalable protocol for the mammalian cell production of ECM proteins with affinity for heparin, using heparin as a supplement. As proof of concept, we have demonstrated the high-level expression of four biomedically relevant human enzymes such as carboxypeptidase Z (CPZ), carboxypeptidase A6 (CPA6), beta-galactoside alpha-2,6-sialyltransferase 2 (ST6GAL1) and thrombin-activable fibrinolysis inhibitor (TAFI). We found a strong linear correlation between the isoelectric point (pI) of a protein and the improvement in protein expression levels upon heparin addition, providing a reference for selecting novel protein targets that would benefit from heparin supplementation. Finally, we demonstrated the compatibility of this approach with a three-step purification strategy that includes an initial heparin affinity purification step. Using CPZ as a representative example, we performed a preparative purification of this enzyme. The purified protein is enzymatically active and can be used for pharmaceutical applications as well as for high-throughput functional and structural studies.

Strategies for efficient production of recombinant proteins in Escherichia coli: alleviating the host burden and enhancing protein activity

Escherichia coli, one of the most efficient expression hosts for recombinant proteins (RPs), is widely used in chemical, medical, food and other industries. However, conventional expression strains are unable to effectively express proteins with complex structures or toxicity. The key to solving this problem is to alleviate the host burden associated with protein overproduction and to enhance the ability to accurately fold and modify RPs at high expression levels. Here, we summarize the recently developed optimization strategies for the high-level production of RPs from the two aspects of host burden and protein activity. The aim is to maximize the ability of researchers to quickly select an appropriate optimization strategy for improving the production of RPs.

Current trends in biopharmaceuticals production in Escherichia coli

Since the manufacture of the first biotech product for a fledgling biopharmaceutical industry in 1982, Escherichia coli, has played an important role in the industrial production of recombinant proteins. It is now 40 years since the introduction of Humulin® for the treatment of diabetes. E. coli remains an important production host, its use as a cell factory is well established and it has become the most popular expression platform particularly for non-glycosylated therapeutic proteins. A number of significant inherent obstacles in the use of prokaryotic expression systems to produce biologics has always restricted production. These include codon usage, the absence of post-translational modifications and proteolytic processing at the cell envelope. In this review, we reflect on the contribution that this model organism has made in the production of new biotech products for human medicine. This will include new advancements in the E. coli expression system to meet the biotechnology industry requirements, such as novel engineered strains to glycosylate heterologous proteins, add disulphide bonds and express complex proteins. The biopharmaceutical market is growing rapidly, with two production systems competing for market dominance: mammalian cells and microorganisms. In the past 10 years, with increased growth of antibody-based therapies, mammalian hosts particularly CHO cells have dominated. However, with new antibody like scaffolds and mimetics emerging as future proteins of interest, E. coli has again the opportunity to be the selected as the production system of choice.

Optimized Production of Disulfide-Bonded Fungal Effectors in Escherichia coli Using CyDisCo and FunCyDisCo Coexpression Approaches

Effectors are a key part of the arsenal of plant-pathogenic fungi and promote pathogen virulence and disease. Effectors typically lack sequence similarity to proteins with known functional domains and motifs, limiting our ability to predict their functions and understand how they are recognized by plant hosts. As a result, cross-disciplinary approaches involving structural biology and protein biochemistry are often required to decipher and better characterize effector function. These approaches are reliant on high yields of relatively pure protein, which often requires protein production using a heterologous expression system. For some effectors, establishing an efficient production system can be difficult, particularly those that require multiple disulfide bonds to achieve their naturally folded structure. Here, we describe the use of a coexpression system within the heterologous host Escherichia coli, termed CyDisCo (cytoplasmic disulfide bond formation in E. coli) to produce disulfide bonded fungal effectors. We demonstrate that CyDisCo and a naturalized coexpression approach termed FunCyDisCo (Fungi CyDisCo) can significantly improve the production yields of numerous disulfide-bonded effectors from diverse fungal pathogens. The ability to produce large quantities of functional recombinant protein has facilitated functional studies and crystallization of several of these reported fungal effectors. We suggest this approach could be broadly useful in the investigation of the function and recognition of a broad range of disulfide bond-containing effectors.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Functional Overexpression of Membrane Proteins in E. coli: The Good, the Bad, and the Ugly

Overexpression of properly folded membrane proteins is a mandatory step for their functional and structural characterization. One of the most used expression systems for the production of proteins is Escherichia coli. Many advantageous strains combined with T7 expression systems have been developed over the years. Recently, we showed that the choice of the strain is critical for the functionality of membrane proteins, even when the proteins are successfully incorporated in the membrane (Mathieu et al. Sci Rep. 2019; 9(1):2654). Notably, the amount and/or activity of the T7-RNA polymerase, which drives the transcription of the genes of interest, may indirectly affect the folding and functionality of overexpressed membrane proteins. Moreover, we reported a general trend in which mild detergents mainly extract the population of active membrane proteins, whereas a harsher detergent like Fos-choline 12 could solubilize them irrespectively of their functionality. Based on these observations, we provide some guidelines to optimize the quality of membrane proteins overexpressed in E. coli.

Microbial protein cell factories fight back?

The biopharmaceutical market is growing faster than ever, with two production systems competing for market dominance: mammalian cells and microorganisms. In recent years, based on the rise of antibody-based therapies, new biotherapeutic approvals have favored mammalian hosts. However, not only has extensive research elevated our understanding of microbes to new levels, but emerging therapeutic molecules also facilitate their use; thus, is it time for microbes to fight back? In this review, we answer this timely question by cross-comparing four microbial production hosts and examining the innovations made to both their secretion and post-translational modification (PTM) capabilities. Furthermore, we discuss the impact of tools, such as omics and systems biology, as well as alternative production systems and emerging biotherapeutics.

Plant antimicrobial peptides: structures, functions, and applications

Antimicrobial peptides (AMPs) are a class of short, usually positively charged polypeptides that exist in humans, animals, and plants. Considering the increasing number of drug-resistant pathogens, the antimicrobial activity of AMPs has attracted much attention. AMPs with broad-spectrum antimicrobial activity against many gram-positive bacteria, gram-negative bacteria, and fungi are an important defensive barrier against pathogens for many organisms. With continuing research, many other physiological functions of plant AMPs have been found in addition to their antimicrobial roles, such as regulating plant growth and development and treating many diseases with high efficacy. The potential applicability of plant AMPs in agricultural production, as food additives and disease treatments, has garnered much interest. This review focuses on the types of plant AMPs, their mechanisms of action, the parameters affecting the antimicrobial activities of AMPs, and their potential applications in agricultural production, the food industry, breeding industry, and medical field.

Challenges Associated With the Formation of Recombinant Protein Inclusion Bodies in Escherichia coli and Strategies to Address Them for Industrial Applications

Recombinant proteins are becoming increasingly important for industrial applications, where Escherichia coli is the most widely used bacterial host for their production. However, the formation of inclusion bodies is a frequently encountered challenge for producing soluble and functional recombinant proteins. To overcome this hurdle, different strategies have been developed through adjusting growth conditions, engineering host strains of E. coli, altering expression vectors, and modifying the proteins of interest. These approaches will be comprehensively highlighted with some of the new developments in this review. Additionally, the unique features of protein inclusion bodies, the mechanism and influencing factors of their formation, and their potential advantages will also be discussed.

Efficient soluble production of folded cat allergen Fel d 1 in Escherichia coli

The major cat allergen Fel d 1 is one of the most common and potent causes of animal related allergy. Medical treatment of cat allergy has relied on immunotherapy carried out with cat dander extract. This approach has been problematic, mainly due to inconsistent levels of the major allergen in the produced extracts. Recombinant DNA technology has been proposed as an alternative method to produce more consistent pharmaceuticals for immunotherapy and diagnostics of allergy. Current approaches to produce recombinant Fel d 1 (recFel d 1) in the cytoplasm of Escherichia coli have however resulted in protein folding deficiencies and insoluble inclusion body formation, requiring elaborate in vitro processing to acquire folded material. In this study, we introduce an efficient method for cytoplasmic production of recFel d 1 that utilizes eukaryotic folding factors to aid recFel d 1 to fold and be produced in the soluble fraction of E. coli. The solubly expressed recFel d 1 is shown by biophysical in vitro experiments to contain structural disulfides, is extremely stable, and has a sensitivity for methionine sulfoxidation. The latter is discussed in the context of functional relevance.