Activity of maize transglutaminase overexpressed in Escherichia coli inclusion bodies: an alternative to protein refolding

Heterologous expression of recombinant nattokinase in Escherichia coli BL21(DE3) and media optimization for overproduction of nattokinase using RSM

Nattokinase, a serine protease, was discovered in Bacillus subtilis during the fermentation of a soybean byproduct. Nattokinase is essential for the lysis of blood clots and the treatment of cardiac diseases including atherosclerosis, thrombosis, high blood pressure, and stroke. The demand for thrombolytic drugs rises as the prevalence of cardiovascular disease rises, and nattokinase is particularly effective for the treatment of cardiovascular diseases due to its long duration of action. In this study, we cloned the nattokinase gene from the Bacillus subtilis strain into the pET32a vector and expressed the protein in the E. coli BL21(DE3) strain. The active recombinant nattokinase was purified using Ni-NTA affinity chromatography and then evaluated for fibrinolytic and blood clot lysis activity. Physiological parameters for optimizing protein production at optimal pH, temperature, IPTG concentration, and incubation time were investigated. A statistical technique was used to optimize media components for nattokinase overproduction, and Central Composite Design-Response Surface Methodology-based optimization was used to select significant components for protein production. The optimized media produced 1805.50 mg/L of expressed nattokinase and 42.80 gm/L of bacterial mass. The fibrinolytic activity obtained from refolded native protein was 58FU/mg, which was five times higher than the available orokinase drug (11FU/mg). The efficiency with which a statistical technique for media optimization was implemented improved recombinant nattokinase production and provides new information for scale - up nattokinase toward industrial applications.

Expression of membrane beta-barrel protein in E. coli at low temperatures: Structure of Yersinia pseudotuberculosis OmpF porin inclusion bodies

The recombinant OmpF porin of Yersinia pseudotuberculosis as a model of transmembrane protein of the β-barrel structural family was used to study low growth temperature effect on the structure of the produced inclusion bodies (IBs). This porin showed a very low expression level in E. coli at a growth temperature below optimal 37 °C. The introduction of a N-terminal hexahistidine tag into the mature porin molecule significantly increased the biosynthesis of the protein at low cultivation temperatures. The recombinant His-tagged porin (rOmpF-His) was expressed in E. coli at 30 and 18 °C as inclusion bodies (IB-30 and IB-18). The properties and structural organization of IBs, as well as the structure of rOmpF-His solubilized from the IBs with urea and SDS, were studied using turbidimetry, electron microscopy, dynamic light scattering, optical spectroscopy, and amyloid-specific dyes. IB-18, in comparison with IB-30, has a higher solubility in denaturants, suggesting a difference between IBs in the conformation of the associated polypeptide chains. The spectroscopic analysis revealed that rOmpF-His IBs have a high content of secondary structure with a tertiary-structure elements, including a native-like conformation, the proportion of which in IB-18 is higher than in IB-30. Solubilization of the porin from IBs is accompanied by a modification of its secondary structure. The studied IBs also contain amyloid-like structures. The results obtained in this study expand our knowledge of the structural organization of IBs formed by proteins of different structural classes and also have a contribution into the new approaches development of producing functionally active recombinant membrane proteins.

Studies on the Structure and Properties of Membrane Phospholipase A1 Inclusion Bodies Formed at Low Growth Temperatures Using GFP Fusion Strategy

The effect of cultivation temperatures (37, 26, and 18 °C) on the conformational quality of Yersinia pseudotuberculosis phospholipase A₁ (PldA) in inclusion bodies (IBs) was studied using green fluorescent protein (GFP) as a folding reporter. GFP was fused to the C-terminus of PldA to form the PldA-GFP chimeric protein. It was found that the maximum level of fluorescence and expression of the chimeric protein is observed in cells grown at 18 °C, while at 37 °C no formation of fluorescently active forms of PldA-GFP occurs. The size, stability in denaturant solutions, and enzymatic and biological activity of PldA-GFP IBs expressed at 18 °C, as well as the secondary structure and arrangement of protein molecules inside the IBs, were studied. Solubilization of the chimeric protein from IBs in urea and SDS is accompanied by its denaturation. The obtained data show the structural heterogeneity of PldA-GFP IBs. It can be assumed that compactly packed, properly folded, proteolytic resistant, and structurally less organized, susceptible to proteolysis polypeptides can coexist in PldA-GFP IBs. The use of GFP as a fusion partner improves the conformational quality of PldA, but negatively affects its enzymatic activity. The PldA-GFP IBs are not toxic to eukaryotic cells and have the property to penetrate neuroblastoma cells. Data presented in the work show that the GFP-marker can be useful not only as target protein folding indicator, but also as a tool for studying the molecular organization of IBs, their morphology, and localization in E. coli, as well as for visualization of IBs interactions with eukaryotic cells.

Structure-Function Relationship of Inclusion Bodies of a Multimeric Protein

High level expression of recombinant proteins in bacteria often results in their aggregation into inclusion bodies. Formation of inclusion bodies poses a major bottleneck in high-throughput recovery of recombinant protein. These aggregates have amyloid-like nature and can retain biological activity. Here, effect of expression temperature on the quality of Escherichia coli asparaginase II (a tetrameric protein) inclusion bodies was evaluated. Asparaginase was expressed as inclusion bodies at different temperatures. Purified inclusion bodies were checked for biological activities and analyzed for structural properties in order to establish a structure-activity relationship. Presence of activity in inclusion bodies showed the existence of properly folded asparaginase tetramers. Expression temperature affected the properties of asparaginase inclusion bodies. Inclusion bodies expressed at higher temperatures were characterized by higher biological activity and less amyloid content as evident by Thioflavin T binding and Fourier Transform Infrared (FTIR) spectroscopy. Complex kinetics of proteinase K digestion of asparaginase inclusion bodies expressed at higher temperatures indicate higher extent of conformational heterogeneity in these aggregates.

Transglutaminases: part I-origins, sources, and biotechnological characteristics

The transglutaminases form a large family of intracellular and extracellular enzymes that catalyze cross-links between protein molecules. Transglutaminases crosslinking properties are widely applied to various industrial processes, to improve the firmness, viscosity, elasticity, and water-holding capacity of products in the food and pharmaceutical industries. However, the extremely high costs of obtaining transglutaminases from animal sources have prompted scientists to search for new sources of these enzymes. Therefore, research has been focused on producing transglutaminases by microorganisms, which may present wider scope of use, based on enzyme-specific characteristics. In this review, we present an overview of the literature addressing the origins, types, reactions, and general characterizations of this important enzyme family. A second review will deal with transglutaminases applications in the area of food industry, medicine, pharmaceuticals and biomaterials, as well as applications in the textile and leather industries.

Expression of Zea mays transglutaminase in Pichia pastoris under different promoters and its impact on properties of acidified milk protein concentrate gel

BACKGROUND

Transglutaminase (TGase) catalyzes post-translational modification of proteins by γ-glutamyl-ϵ-lysine chain links, covalent conjugation of polyamines, and deamidation. Zea mays TGase (TGZ) is a plant TGase with potential application prospects in the food industry. In this study, two promoter types, P_FLD1 and P_TEF1 , were compared to improve the expression of TGZ, and the cross-linking effect of recombinant TGZ on the properties of acid-induced milk protein concentrate (MPC) gel was assessed.

RESULTS

A higher expression of TGZ was obtained under the induction of P_FLD1 with a production of 635 U L^-1 . After purification using chromatography, TGZ activity was 0.4 U mg^-1 . The results indicated that TGZ treatment has effectively improved the textural properties of MPC gel at strength level and water-holding capacity. Optimal texture of MPC gel was achieved after TGZ treatment using 2 U g^-1 TGZ for 2 h at 35 °C and pH 7.

CONCLUSION

Comparative analysis of the promoters has greatly contributed to the production of TGZ in the industrial field. Furthermore, the modification of MPC gel texture by TGZ indicated that this recombinant enzyme has a practical value in dairy product, especially in yoghurt industry. © 2019 Society of Chemical Industry.

Classification of microbial transglutaminases by evaluation of evolution trees, sequence motifs, secondary structure topology and conservation of potential catalytic residues

Despite the growing interest for microbial transglutaminases (TGases), and the large number of genome sequencing data, there is no deep investigation about structural properties within this family of enzymes in bacteria. We performed a classification of microbial TGases, starting from large-scale analysis of all protein sequences annotated as TGase (more than 8000) in database PFAM. We developed a reiterative procedure based on the construction of several phylogenetic trees and manual selection, and detected five main groups of microbial TGases. Searches for sequence motifs evidenced strong conservation in regions containing potential catalytic residues for some groups. Protein structure modelling has been possible for three of the five groups. Analyses of motifs, structural topologies and potential catalytic sites suggest possible interpretations for function similarities and divergences among groups.

Wanted: more monitoring and control during inclusion body processing

Inclusion bodies (IBs) are insoluble aggregates of misfolded protein in Escherichia coli. Against the outdated belief that the production of IBs should be avoided during recombinant protein production, quite a number of recombinant products are currently produced as IBs, which are then processed to give correctly folded and soluble product. However, this processing is quite cumbersome comprising IB wash, IB solubilization and refolding. To date, IB processing often happens rather uncontrolled and relies on empiricism rather than sound process understanding. In this mini review we describe current efforts to introduce more monitoring and control in IB processes, focusing on the refolding step, and thus generate process understanding and knowledge.

Specific mutation of transglutaminase gene from Streptomyces hygroscopicus H197 and characterization of microbial transglutaminase

Microbial transglutaminase (MTG) gene (mtg) from Streptomyces hygroscopicus H197 strain was cloned by PCR and mutated by deleting a specific 84 bp fragment using overlapping extension PCR. The mutant MTG and the wild MTG genes expressed by recombinant plasmid pET32a+- mutant mtg and pET32a+ -mtg, respectively, and were harvested by alternating freeze-thaw steps and purified by Ni column. The purified mutant MTG and the wild MTG exhibited 0.22 U/mg and 0.16 U/mg activity, respectively, and 0.69 U/mg and 0.54 U/mg activity, respectively, after activated by trypsin. The molecular weight of mutant MTG was estimated as 67 kDa by SDS-PAGE. Both MTGs showed optimum activity at pH 6-8 for hydroxamate formation from N-CBZ-Gln-Gly and hydroxylamine, and exhibited higher stability at 40°C and 1-3% salinity. The two types of MTG were not stable in the presence of Zn(II), Cu(II), Hg(II), Pb(II), Fe(III), and Ag(I), suggesting that they could possess a thiol group. In addition, the mutant MTG and the wild MTG were strongly affected by ethanol. Furthermore, the mutant MTG was obviously (P less than 0.05 or P less than 0.01) more stable than the wild MTG at 50°C and 60°C, at pH 4, 5, and 9, at 7 % and 9 % salinity, 30 % and 35 % ethanol concentration, and in the presence of Li(I) and Ag(I). The polyhydroxy compounds as protein stabilizers could elevate MTG stability.

Optimization of recombinant Zea mays transglutaminase production and its influence on the functional properties of yogurt

The requirements for the production of optimized Zea mays transglutaminase (TGZo) using Pichia pastoris GS115 (pPIC9K-tgzo) were optimized in this study. Plackett-Burman design was used to screen variables that significantly influence TGZo production. Oleic acid, methanol, and loading volume were identified as the most significant parameters. Central composite design was employed to determine the optimal level of these three parameters for TGZo production. Results showed that 1078 mU/mL of TGZo activity and 7.6 mg/L of TGZo production were obtained under conditions of 0.07% oleic acid, 1.31% methanol, and 7.36% loading volume. To explore the functional characteristics of TGZo, it was used in yogurt. It was found that the addition of TGZo could produce yogurt with stronger acid gel and higher consistency, cohesiveness, index of viscosity, and apparent viscosity than the untreated product. Therefore, TGZo can be used as a substitute for microbial transglutaminase in the yogurt, even in the food industry.

Transglutaminases in Dysbiosis As Potential Environmental Drivers of Autoimmunity

Protein-glutamine γ-glutamyltransferases (transglutaminases, Tgs) belong to the class of transferases. They catalyze the formation of an isopeptide bond between the acyl group at the end of the side chain of protein- or peptide-bound glutamine residues and the first order 𝜀-amine groups of protein- or peptide-bound lysine. The Tgs are considered to be universal protein cross-linkers, and they play an essential role in a number of human diseases. In this review, we discuss mainly the bacterial Tgs in terms of the functionality of the enzymes and a potential role they may play in bacterial survival. Since microbial transglutaminases (mTgs) are functionally similar to the human homologs, they may be involved in the human disease provocation. We suggest here a potential involvement of Tgs in the pathologies such as autoimmune diseases. In this hypothesis, the endogenous mTgs that are secreted by the gut microbiota, especially in a dysbiotic configuration, are potential drivers of systemic autoimmunity, via the enzymatic posttranslational modification of peptides in the gut lumen. These mTg activities directed toward cross-linking of naïve proteins can potentially generate neo-epitopes that are not only immunogenic but may also activate some immune response cascades leading to the pathological autoimmune processes.

Protein recovery from inclusion bodies of Escherichia coli using mild solubilization process

Formation of inclusion bodies in bacterial hosts poses a major challenge for large scale recovery of bioactive proteins. The process of obtaining bioactive protein from inclusion bodies is labor intensive and the yields of recombinant protein are often low. Here we review the developments in the field that are targeted at improving the yield, as well as quality of the recombinant protein by optimizing the individual steps of the process, especially solubilization of the inclusion bodies and refolding of the solubilized protein. Mild solubilization methods have been discussed which are based on the understanding of the fact that protein molecules in inclusion body aggregates have native-like structure. These methods solubilize the inclusion body aggregates while preserving the native-like protein structure. Subsequent protein refolding and purification results in high recovery of bioactive protein. Other parameters which influence the overall recovery of bioactive protein from inclusion bodies have also been discussed. A schematic model describing the utility of mild solubilization methods for high throughput recovery of bioactive protein has also been presented.

Proteomic and transcriptomic analysis of rice tranglutaminase and chloroplast-related proteins

The recently cloned rice transglutaminase gene (tgo) is the second plant transglutaminase identified to date (Campos et al. Plant Sci. 205-206 (2013) 97-110). Similarly to its counterpart in maize (tgz), this rice TGase was localized in the chloroplast, although in this case not exclusively. To further characterise plastidial tgo functionality, proteomic and transcriptomic studies were carried out to identify possible TGO-related proteins. Some LHCII antenna proteins were identified as TGO related using an in vitro proteomic approach, as well as ATPase and some PSII core proteins by mass spectrometry. To study the relationship between TGO and other plastidial proteins, a transcriptomic in vivo Dynamic Array (Fluidigm™) was used to analyse the mRNA expression of 30 plastidial genes with respect to that of tgo, in rice plants subjected to different periods of continuous illumination. The results indicated a gene-dependent tendency in the expression pattern that was related to tgo expression and to the illumination cycle. For certain genes, including tgo, significant differences between treatments, principally at the initiation and/or at the end of the illumination period, connected with the day/night cycling of gene expression, were observed. The tgo expression was especially related to plastidial proteins involved in photoprotection and the thylakoid electrochemical gradient.

Transglutaminases: recent achievements and new sources

Transglutaminases are a family of enzymes (EC 2.3.2.13), widely distributed in various organs, tissues, and body fluids, that catalyze the formation of a covalent bond between a free amine group and the γ-carboxamide group of protein or peptide-bound glutamine. Besides forming these bonds, that exhibit high resistance to proteolytic degradation, transglutaminases also form extensively cross-linked, generally insoluble, protein biopolymers that are indispensable for the organism to create barriers and stable structures. The extremely high cost of transglutaminase of animal origin has hampered its wider application and has initiated efforts to find an enzyme of microbial origin. Since the early 1990s, many microbial transglutaminase-producing strains have been found, and production processes have been optimized. This has resulted in a rapidly increasing number of applications of transglutaminase in the food sector. However, applications of microbial transglutaminase in other sectors have also been explored, but in a much lesser extent. Our group has identified a transglutaminase in the oomycete Phytophthora cinnamomi, which is able to induct defense responses and disease-like symptoms. In this mini-review, we report the achievements in this area in order to illustrate the importance and the versatility of transglutaminases.

Characterization of recombinant Zea mays transglutaminase expressed in Pichia pastoris and its impact on full and non-fat yoghurts

BACKGROUND

Transglutaminases catalyze post-translational modification of proteins by ε-(γ-glutamyl) links and covalent amide bonds. Research on properties and applications of plant transglutaminases is less developed than in animals and micro-organisms. In a previous study, optimized Zea mays transglutaminase was purified from recombinant Pichia pastoris strain. The main objective of the present study was to characterize this enzyme and assess its effect on the properties of yoghurt.

RESULTS

The purified recombinant transglutaminase presented a Km of 3.98 µmol L(-1) and a Vmax of 2711 min(-1) by the fluorometric method. The enzyme was stable after incubation for 30 min below 50 °C and over a broad pH range of 5-8 at -20 °C for 12 h. The results showed that the crosslinking reaction catalyzed by this enzyme could effectively improve the properties of full and non-fat yoghurts. Also, the properties of non-fat yoghurt could be improved similar to the full-fat product by recombinant transglutaminase.

CONCLUSION

The application of recombinant transglutaminase in yoghurt indicated that this enzyme could be used as a substitute for microbial transglutaminase in the production of yoghurt, thus providing experimental evidence for the future application of plant transglutaminases in the food industry.

pH-dependent activation of Streptomyces hygroscopicus transglutaminase mediated by intein

Microbial transglutaminase (MTG) from Streptomyces is naturally secreted as a zymogen (pro-MTG), which is then activated by the removal of its N-terminal proregion by additional proteases. Inteins are protein-intervening sequences that catalyze protein splicing without cofactors. In this study, a pH-dependent Synechocystis sp. strain PCC6803 DnaB mini-intein (SDB) was introduced into pro-MTG to simplify its activation process by controlling pH. The recombinant protein (pro-SDB-MTG) was obtained, and the activation process was determined to take 24 h at pH 7 in vitro. To investigate the effect of the first residue in MTG on the activity and the cleavage time, two variants, pro-SDB-MTG(D1S) and pro-SDB-MTG(ΔD1), were expressed, and the activation time was found to be 6 h and 30 h, respectively. The enzymatic property and secondary structure of the recombinant MTG and two variants were similar to those of the wild type, indicating that the insertion of mini-intein did not affect the function of MTG. This insignificant effect was further illustrated by molecular dynamics simulations. This study revealed a controllable and effective strategy to regulate the activation process of pro-MTG mediated by a mini-intein, and it may have great potential for industrial MTG production.

Rice transglutaminase gene: Identification, protein expression, functionality, light dependence and specific cell location

Transglutaminases (TGases), that catalyze post-translational modification of proteins, are scarcely known in plants. As part of a project to characterize transglutaminase genes in new plant species, the identification and characterization of a TGase in rice is presented. Using differential primers, a cDNA (tgo) of 1767bp from genomic rice DNA amplification was obtained. The primers were designed from the rice DNA sequence relatively homologous to the gene encoding active maize chloroplast TGase. Amino acid sequence of the deduced rice TGase protein (TGO) indicated that it contains the enzyme catalytic triad (Cys-His-Asp), three repeats, myristoylation domains and a leucine zipper motif. The TGO recombinant protein was characterized, showing specific activity regulation, and indicating that tgo encoded for an authentic TGase. Substrate preference and Ca(2+) dependent activity were also detected. In the rice plant TGO protein was immunolocalized in the grana chloroplasts, in protein vesicles near them, and in the bulliform cells. Immunoblot analyses, tgo mRNA expression, and TGase activity indicated that TGO expression in rice was light dependent and regulated by the illumination period. This work increases significantly our plant TGase understanding. Its functional role in rice, which is a good model system for C3 plants, is discussed.

Role of plastid transglutaminase in LHCII polyamination and thylakoid electron and proton flow

Transglutaminases function as biological glues in animal cells, plant cells and microbes. In energy producing organelles such as chloroplasts the presence of transglutaminases was recently confirmed. Furthermore, a plastidial transglutaminase has been cloned from maize and the first plants overexpressing tgz are available (Nicotiana tabacum TGZ OE). Our hypothesis is that the overexpression of plastidal transglutaminase will alter photosynthesis via increased polyamination of the antenna of photosystem II. We have used standard analytical tools to separate the antenna from photosystem II in wild type and modified plants, 6 specific antibodies against LHCbs to confirm their presence and sensitive HPLC method to quantify the polyamination level of these proteins. We report that bound spermidine and spermine were significantly increased (∼80%) in overexpressors. Moreover, we used recent advances in in vivo probing to study simultaneously the proton and electron circuit of thylakoids. Under physiological conditions overexpressors show a 3-fold higher sensitivity of the antenna down regulation loop (qE) to the elicitor (luminal protons) which is estimated as the ΔpH component of thylakoidal proton motive force. In addition, photosystem (hyper-PSIIα) with an exceptionally high antenna (large absorption cross section), accumulate in transglutaminase over expressers doubling the rate constant of light energy utilization (Kα) and promoting thylakoid membrane stacking. Polyamination of antenna proteins is a previously unrecognized mechanism for the modulation of the size (antenna absorption cross section) and sensitivity of photosystem II to down regulation. Future research will reveal which peptides and which residues of the antenna are responsible for such effects.

Kinetics of inclusion body formation and its correlation with the characteristics of protein aggregates in Escherichia coli

The objective of the research was to understand the structural determinants governing protein aggregation into inclusion bodies during expression of recombinant proteins in Escherichia coli. Recombinant human growth hormone (hGH) and asparaginase were expressed as inclusion bodies in E.coli and the kinetics of aggregate formation was analyzed in details. Asparaginase inclusion bodies were of smaller size (200 nm) and the size of the aggregates did not increase with induction time. In contrast, the seeding and growth behavior of hGH inclusion bodies were found to be sequential, kinetically stable and the aggregate size increased from 200 to 800 nm with induction time. Human growth hormone inclusion bodies showed higher resistance to denaturants and proteinase K degradation in comparison to those of asparaginase inclusion bodies. Asparaginase inclusion bodies were completely solubilized at 2–3 M urea concentration and could be refolded into active protein, whereas 7 M urea was required for complete solubilization of hGH inclusion bodies. Both hGH and asparaginase inclusion bodies showed binding with amyloid specific dyes. In spite of its low β-sheet content, binding with dyes was more prominent in case of hGH inclusion bodies than that of asparaginase. Arrangements of protein molecules present in the surface as well as in the core of inclusion bodies were similar. Hydrophobic interactions between partially folded amphiphillic and hydrophobic alpha-helices were found to be one of the main determinants of hGH inclusion body formation. Aggregation behavior of the protein molecules decides the nature and properties of inclusion bodies.

The order of expression is a key factor in the production of active transglutaminase in Escherichia coli by co-expression with its pro-peptide

Background

Streptomyces transglutaminase (TGase) is naturally synthesized as zymogen (pro-TGase), which is then processed to produce active enzyme by the removal of its N-terminal pro-peptide. This pro-peptide is found to be essential for overexpression of soluble TGase in E. coli. However, expression of pro-TGase by E. coli requires protease-mediated activation in vitro. In this study, we developed a novel co- expression method for the direct production of active TGase in E. coli.

Results

A TGase from S. hygroscopicus was expressed in E. coli only after fusing with the pelB signal peptide, but fusion with the signal peptide induced insoluble enzyme. Therefore, alternative protocol was designed by co-expressing the TGase and its pro-peptide as independent polypeptides under a single T7 promoter using vector pET-22b(+). Although the pro-peptide was co-expressed, the TGase fused without the signal peptide was undetectable in both soluble and insoluble fractions of the recombinant cells. Similarly, when both genes were expressed in the order of the TGase and the pro-peptide, the solubility of TGase fused with the signal peptide was not improved by the co-expression with its pro-peptide. Interestingly, active TGase was only produced by the cells in which the pro-peptide and the TGase were fused with the signal peptide and sequentially expressed. The purified recombinant and native TGase shared the similar catalytic properties.

Conclusions

Our results indicated that the pro-peptide can assist correct folding of the TGase inter-molecularly in E. coli, and expression of pro-peptide prior to that of TGase was essential for the production of active TGase. The co-expression strategy based on optimizing the order of gene expression could be useful for the expression of other functional proteins that are synthesized as a precursor.

Active protein aggregates produced in Escherichia coli

Since recombinant proteins are widely used in industry and in research, the need for their low-cost production is increasing. Escherichia coli is one of the best known and most often used host organisms for economical protein production. However, upon over-expression, protein aggregates called inclusion bodies (IBs) are often formed. Until recently IBs formation represented a bottleneck in protein production as they were considered as deposits of inactive proteins. However, recent studies show that by choosing the appropriate host strain and designing an optimal production process, IBs composed from properly folded and biologically active recombinant proteins can be prepared. Such active protein particles can be further used for the isolation of pure proteins or as whole active protein particles in various biomedical and other applications. Therefore interest in understanding the mechanisms of their formation as well as their properties is increasing.

Solubilization of inclusion body proteins using n-propanol and its refolding into bioactive form

Inclusion bodies of recombinant human growth hormone (r-hGH) were isolated from Escherichia coli, enriched and solubilized in 100mM Tris buffer containing 6M n-propanol and 2M urea. Around 4 mg/ml of r-hGH from inclusion bodies were solubilized in 6M n-propanol-based buffer containing 2M urea. Existence of native-like secondary structure of r-hGH in 6M n-propanol solution was confirmed by CD and fluorescence spectra. Solubilized r-hGH was subsequently refolded by pulsatile dilution, purified to homogeneity and found to be functionally active. Tris buffer containing 6M n-propanol and 2M urea also effectively solubilized a number of proteins expressed as inclusion bodies in E. coli. Mild solubilization of inclusion body proteins, chaotropic effect of n-propanol at high concentration and kosmotropic effect at lower concentration helped in improved refolding of the solubilized protein. Around 40% of the r-hGH in the form of inclusion body aggregates was refolded into bioactive form while using n-propanol as solubilization agent. Solubilization with 6M n-propanol solution thus can be a viable alternative for achieving high throughput recovery of bioactive protein from inclusion bodies of E. coli.