Integrated continuous dissolution, refolding and tag removal of fusion proteins from inclusion bodies in a tubular reactor

An integrated continuous tubular reactor system was developed for processing an autoprotease expressed as inclusion bodies. The inclusion bodies were suspended and fed into the tubular reactor system for continuous dissolving, refolding and precipitation. During refolding, the dissolved autoprotease cleaves itself, separating the fusion tag from the target peptide. Subsequently, the cleaved fusion tag and any uncleaved autoprotease were precipitated out in the precipitation step. The processed exiting solution results in the purified soluble target peptide. Refolding and precipitation yields performed in the tubular reactor were similar to batch reactor and process was stable for at least 20 h. The authenticity of purified peptide was also verified by mass spectroscopy. Productivity (in mg/l/h and mg/h) calculated in the tubular process was twice and 1.5 times of the batch process, respectively. Although it is more complex to setup a tubular than a batch reactor, it offers faster mixing, higher productivity and better integration to other bioprocessing steps. With increasing interest of integrated continuous biomanufacturing, the use of tubular reactors in industrial settings offers clear advantages.

A successful strategy for the recovering of active P21, an insoluble recombinant protein of Trypanosoma cruzi

Structural studies of proteins normally require large quantities of pure material that can only be obtained through heterologous expression systems and recombinant technique. In these procedures, large amounts of expressed protein are often found in the insoluble fraction, making protein purification from the soluble fraction inefficient, laborious, and costly. Usually, protein refolding is avoided due to a lack of experimental assays that can validate correct folding and that can compare the conformational population to that of the soluble fraction. Herein, we propose a validation method using simple and rapid 1D ¹H nuclear magnetic resonance (NMR) spectra that can efficiently compare protein samples, including individual information of the environment of each proton in the structure.

Refolding techniques for recovering biologically active recombinant proteins from inclusion bodies

Biologically active proteins are useful for studying the biological functions of genes and for the development of therapeutic drugs and biomaterials in a biotechnology industry. Overexpression of recombinant proteins in bacteria, such as Escherichia coli, often results in the formation of inclusion bodies, which are protein aggregates with non-native conformations. As inclusion bodies contain relatively pure and intact proteins, protein refolding is an important process to obtain active recombinant proteins from inclusion bodies. However, conventional refolding methods, such as dialysis and dilution, are time consuming and, often, recovered yields of active proteins are low, and a trial-and-error process is required to achieve success. Recently, several approaches have been reported to refold these aggregated proteins into an active form. The strategies largely aim at reducing protein aggregation during the refolding procedure. This review focuses on protein refolding techniques using chemical additives and laminar flow in microfluidic chips for the efficient recovery of active proteins from inclusion bodies.

Monoclonal antibody preparation and expression profile analysis of a novel hepatoma associated gene

Hepatoma associated gene (HTA), a gene screened and cloned by our previous research, was specifically expressed in certain kinds of tumors and had a cancer-promoting role in hepatocellular carcinoma (HCC). To further elucidate the mechanism of HTA in hepatoma carcinogenesis and its potential role as a cancer biomarker, refolded HTA protein (HTA) was obtained by prokaryotic recombinant expression system and immobilized metal affinity chromatography. Then anti-HTA monoclonal antibody (mAb) was produced by hybridoma technique. Using the high titer anti-HTA mAb with high specificity obtained, the expression profile of HTA was analysed by immunohistochemistry staining. It showed that HTA expressed specifically in some kinds of tumors, and didn't express in almost any of the normal tissues. The positive expression rate and expression quantity of HTA was significantly higher in HCC tissues than in hepatic cirrhosis tissues, hepatic fibrosis tissues and normal hepatic tissues. The expression of HTA was positively correlated with hepatoma carcinogenic process.

Effect of controlled redox potential and dissolved oxygen on the in vitro refolding of an E. coli alkaline phosphatase and chicken lysozyme

The development of efficient purification strategies of recombinant active protein derived from inclusion bodies requires the knowledge of the effect of environmental variables, such as redox potential (RP) and dissolved oxygen tension (DOT), in order to control the protein folding process. However, that information is scarce and only few in vitro studies of the impact of such variables have been reported under constant controlled conditions. In this work, the effect of controlled RP and DOT on the refolding of E. coli alkaline phosphatase (AP) and chicken lysozyme (CL) enzymes were studied. Disulphide bonds of both enzymes were reduced in an instrumented vessel using 2-mercaptoethanol and nitrogen. In the latter case, guanidine hydrochloride was also used to denature the protein. Such conditions caused protein conformational changes, as determined by the intrinsic fluorescence spectra that correlated with a decrease on the activity in both cases. Reduced enzymes were then oxidized, under different constant and predetermined RP or DOT, by manipulating the gas composition in the vessel. Folding kinetics were followed as the recovery of enzyme activity. Results showed that the percentage of recovery and rate of increase of enzymatic activity directly depended on the RP and DOT. A higher folding efficiency was found under controlled DOT compared to controlled RP conditions. These results are useful for establishing protein folding strategies to improve the recovery of active protein from inclusion bodies.

A multipurpose fusion tag derived from an unstructured and hyperacidic region of the amyloid precursor protein

Expression and purification of aggregation-prone and disulfide-containing proteins in Escherichia coli remains as a major hurdle for structural and functional analyses of high-value target proteins. Here, we present a novel gene-fusion strategy that greatly simplifies purification and refolding procedure at very low cost using a unique hyperacidic module derived from the human amyloid precursor protein. Fusion with this polypeptide (dubbed FATT for Flag-Acidic-Target Tag) results in near-complete soluble expression of variety of extracellular proteins, which can be directly refolded in the crude bacterial lysate and purified in one-step by anion exchange chromatography. Application of this system enabled preparation of functionally active extracellular enzymes and antibody fragments without the need for condition optimization.

Antigen generation and display in therapeutic antibody drug discovery -- a neglected but critical player

Disease intervention by targeting a critical pathway molecule through a blocking antibody or interference by therapeutic proteins is currently en vogue. Generation of blocking antibodies or therapeutic proteins inevitably requires the production of recombinant proteins or cell-based immunogens. Thus, one could call the antigen molecule the neglected player in antibody drug discovery. The variety of methods available for making recombinant proteins or recombinant cell lines that present the target on the cell surface is extensive. These need to be addressed in conjunction with biochemical and biophysical quality criteria and the experimental application intended. Fundamentally, successful production and isolation of monoclonal antibodies requires optimized antigen preparation and presentation to the immune host. This review summarizes the most important aspects of antigen generation and display, enabling logical decision making to give rise to potent high-affinity antibodies.

Industrial production of recombinant therapeutics in Escherichia coli and its recent advancements

Nearly 30% of currently approved recombinant therapeutic proteins are produced in Escherichia coli. Due to its well-characterized genetics, rapid growth and high-yield production, E. coli has been a preferred choice and a workhorse for expression of non-glycosylated proteins in the biotech industry. There is a wealth of knowledge and comprehensive tools for E. coli systems, such as expression vectors, production strains, protein folding and fermentation technologies, that are well tailored for industrial applications. Advancement of the systems continues to meet the current industry needs, which are best illustrated by the recent drug approval of E. coli produced antibody fragments and Fc-fusion proteins by the FDA. Even more, recent progress in expression of complex proteins such as full-length aglycosylated antibodies, novel strain engineering, bacterial N-glycosylation and cell-free systems further suggests that complex proteins and humanized glycoproteins may be produced in E. coli in large quantities. This review summarizes the current technology used for commercial production of recombinant therapeutics in E. coli and recent advances that can potentially expand the use of this system toward more sophisticated protein therapeutics.

Methods for chromatographic removal of endotoxin

Endotoxin removal is critical when producing therapeutic proteins in bacterial systems. This hydrophobic compound can be removed through chromatography or filtration, but presents unique challenges dependent upon protein composition as well as production scale. Here we present a robust method for endotoxin removal at the pilot production scale using fast protein liquid chromatography and buffers specifically engineered for endotoxin removal.

Increasing recombinant protein production in Escherichia coli through metabolic and genetic engineering

Different hosts have been used for recombinant protein production, ranging from simple bacteria, such as Escherichia coli and Bacillus subtilis, to more advanced eukaryotes as Saccharomyces cerevisiae and Pichia pastoris, to very complex insect and animal cells. All have their advantages and drawbacks and not one seems to be the perfect host for all purposes. In this review we compare the characteristics of all hosts used in commercial applications of recombinant protein production, both in the area of biopharmaceuticals and industrial enzymes. Although the bacterium E. coli remains a very often used organism, several drawbacks limit its possibility to be the first-choice host. Furthermore, we show what E. coli strains are typically used in high cell density cultivations and compare their genetic and physiological differences. In addition, we summarize the research efforts that have been done to improve yields of heterologous protein in E. coli, to reduce acetate formation, to secrete the recombinant protein into the periplasm or extracellular milieu, and to perform post-translational modifications. We conclude that great progress has been made in the incorporation of eukaryotic features into E. coli, which might allow the bacterium to regain its first-choice status, on the condition that these research efforts continue to gain momentum.

Amniotic liquid derived stem cells as reservoir of secreted angiogenic factors capable of stimulating neo-arteriogenesis in an ischemic model

Most urgent health problems are related to a blood vessel formation failure. The use of stem cells from different sources or species for both in vitro and in vivo engineering of endothelium does not necessarily imply their direct commitment towards a vascular phenotype. In the present study, we used human amniotic fluid stem cells (AFSC) to evoke a strong angiogenic response in murine recipients, in terms of host guided-regeneration of new vessels, and we demonstrated that the AFSC secretome is responsible for the vascularising properties of these cells. We indentified in AFSC conditioned media (ACM) pro-angiogenic soluble factors, such as MCP-1, IL-8, SDF-1, VEGF. Our in vitro results suggest that ACM are cytoprotective, pro-differentiative and chemoattractive for endothelial cells. We also tested ACM on a pre-clinical model of hind-limb ischemic mouse, concluding that ACM contain mediators that promote the neo-arteriogenesis, as remodelling of pre-existing collateral arteries to conductance vessels, thus preventing the capillary loss and the tissue necrosis of distal muscles. In line with the current regenerative medicine trend, in the present study we assert the concept that stem cell-secreted mediators can guide the tissue repair by stimulating or recruiting host reparative cells.

Alpha casein micelles show not only molecular chaperone-like aggregation inhibition properties but also protein refolding activity from the denatured state

Casein micelles are a major component of milk proteins. It is well known that casein micelles show chaperone-like activity such as inhibition of protein aggregation and stabilization of proteins. In this study, it was revealed that casein micelles also possess a high refolding activity for denatured proteins. A buffer containing caseins exhibited higher refolding activity for denatured bovine carbonic anhydrase than buffers including other proteins. In particular, a buffer containing α-casein showed about a twofold higher refolding activity compared with absence of α-casein. Casein properties of surface hydrophobicity, a flexible structure and assembly formation are thought to contribute to this high refolding activity. Our results indicate that casein micelles stabilize milk proteins by both chaperone-like activity and refolding properties.