Optimization of inclusion body solubilization and renaturation of recombinant human growth hormone from Escherichia coli

Techno-economic evaluation of an inclusion body solubilization and recombinant protein refolding process

Expression of recombinant proteins in Escherichia coli is normally accompanied by the formation of inclusion bodies (IBs). To obtain the protein product in an active (native) soluble form, the IBs must be first solubilized, and thereafter, the soluble, often denatured and reduced protein must be refolded. Several technically feasible alternatives to conduct IBs solubilization and on-column refolding have been proposed in recent years. However, rarely these on-column refolding alternatives have been evaluated from an economical point of view, questioning the feasibility of their implementation at a preparative scale. The presented study assesses the economic performance of four distinct process alternatives that include pH induced IBs solubilization and protein refolding (pH_IndSR); IBs solubilization using urea, dithiothreitol (DTT), and alkaline pH followed by batch size-exclusion protein refolding; inclusion bodies (IBs) solubilization using urea, DTT, and alkaline pH followed by simulated moving bed (SMB) size-exclusion protein refolding, and IBs solubilization using urea, DTT and alkaline pH followed by batch dilution protein refolding. The economic performance was judged on the basis of the direct fixed capital, and the production cost per unit of product (P(C)). This work shows that (1) pH_IndSR system is a relatively economical process, because of the low IBs solubilization cost; (2) substituting β-mercaptoethanol for dithiothreithol is an attractive alternative, as it significantly decreases the product cost contribution from the IBs solubilization; and (3) protein refolding by size-exclusion chromatography becomes economically attractive by changing the mode of operation of the chromatographic reactor from batch to continuous using SMB technology.

A study on the functional interaction between the GH/PRL family of polypeptides with their receptors in zebrafish: Evidence against GHR1 being the receptor for somatolactin

The growth hormone (GH)/prolactin (PRL) family of polypeptide hormones plays important roles in many aspects of vertebrate physiology. In fish, there is an additional member in this family called somatolactin (SL). Specifically, zebrafish contains five ligands (GH, SLα, SLβ, PRL1 and PRL2) and four cognate receptors including two GH receptors (GHR1 and GHR2) and two PRL receptors (PRLR1 and PRLR2). There is much controversy regarding whether one of the two GHRs in teleosts is in fact the receptor of SL. A multitude of different assay methods were employed to study the functional interaction among these ligands and their receptors in zebrafish. These include assessment of the binding between the ligands and the extracellular domains of the receptors using His-tag pulldown assays, activation of receptor-evoked promoter activities by treatment of the receptor-transfected cells with the recombinant hormones, and phosphorylation of post-receptor signaling factors by treatment of receptor-transfected cells with the recombinant hormones. The results showed that the zebrafish GH can only interact with the GHRs and the zebrafish PRLs can only interact with the PRLRs. The zebrafish SLs, found to be biologically active in another assay, were found to be ineffective in interacting with the zebrafish GHRs and PRLRs. Our data argue against the hypothesis that GHR1 is the SL receptor.

A novel protein refolding system using lauroyl-l-glutamate as a solubilizing detergent and arginine as a folding assisting agent

More than 50 detergents, including acylated amino acid derivatives, were screened for their ability to solubilize and refold recombinant proteins expressed as inclusion bodies. Two model proteins, human interleukin-6 and microbial transglutaminase, were solubilized by these detergents and the solubilized proteins were rapidly diluted for testing their solubilization and refolding effectiveness. Long chain-acylated amino acid derivatives having dicarboxylic acid moieties were found to be superior to others under the conditions tested. In particular, lauroyl-l-glutamate (C12-l-Glu) showed the highest recovery of the native proteins. The effectiveness of dilution refolding was greatly improved by adding aggregation suppressive arginine into the refolding solvents. To gain understanding how this detergent works, interactions between detergents and proteins were examined using spectroscopic and native gel electrophoretic analyses, showing ideal properties for C12-l-Glu as a solubilzing agent, i.e. highly reversible nature of the detergent binding to the model globular proteins and of the conformational changes. These properties most likely have contributed to the effective protein solubilzation and refolding of inclusion bodies using C12-l-Glu and arginine.

Enzyme replacement therapy for Morquio A: an active recombinant N-acetylgalactosamine-6-sulfate sulfatase produced in Escherichia coli BL21

Mucopolysaccharidosis IVA (MPS IVA) is an autosomal recessive disorder caused by N-acetylgalactosamine-6-sulfate sulfatase (GALNS) deficiency. Currently no effective therapies exist for MPS IVA. In this work, production of a recombinant GALNS enzyme (rGALNS) in Escherichia coli BL21 strain was studied. At shake scale, the effect of glucose concentration on microorganism growth, and microorganism culture and induction times on rGALNS production were evaluated. At bench scale, the effect of aeration and agitation on microorganism growth, and culture and induction times were evaluated. The highest enzyme activity levels at shake scale were observed in 12 h culture after 2-4 h induction. At bench scale the highest enzyme activity levels were observed after 2 h induction. rGALNS amounts in inclusion bodies fraction were up to 17-fold higher than those observed in the soluble fraction. However, the highest levels of active enzyme were found in the soluble fraction. Western blot analysis showed the presence of a 50-kDa band, in both soluble and inclusion bodies fractions. These results show for the first time the feasibility and potential of production of active rGALNS in a prokaryotic system for development of enzyme replacement therapy for MPS IVA disease.

High-level expression of barley beta-D-glucan exohydrolase HvExoI from a codon-optimized cDNA in Pichia pastoris

The native beta-d-glucan exohydrolase isoenzyme ExoI from barley seedlings, designated HvExoI, was the first GH3 glycoside hydrolase, for which a crystal structure was determined. A precise understanding of relationships between structure and function in this enzyme has been gained by structural and enzymatic studies. To allow testing of hypotheses gained from these studies, an efficient system for expression of HvExoI in Pichia pastoris was developed using a codon-optimized cDNA. Protein expression at a temperature of 20 degrees C yielded a recombinant enzyme, designated rHvExoI, which had molecular masses of 70-110 kDa due to heavy glycosylation at Asn221, Asn498 and Asn600, the three sites of N-glycosylation in native HvExoI. Most of the N-linked carbohydrate could be removed from rHvExoI, resulting in N-deglycosylated rHvExoI with a substantially decreased molecular mass of 67 kDa. rHvExoI was able to hydrolyse barley (1,3;1,4)-beta-D-glucan, laminarin and lichenans. The catalytic efficiency value k(cat)/K(M) of rHvExoI with barley (1,3;1,4)-beta-D-glucan was similar to that reported for native HvExoI. Further, laminaribiose, cellobiose and gentiobiose were formed through transglycosylation reactions with 4-nitrophenyl beta-D-glucoside and barley (1,3;1,4)-beta-D-glucan. Overall, the biochemical properties of rHvExoI were similar to those reported for native HvExoI, although differences were seen in thermostabilities and hydrolytic rates of certain beta-linked glucosides.

Investigation of inclusion body formation in recombinant Escherichia coli with a bioimaging system

A bioimaging system using giant protoplasts of recombinant Escherichia coli was developed for examining conditions affecting the formation of inclusion bodies. After the giant protoplasts were prepared, isopropyl-beta-d-thiogalactopyranoside (IPTG) was used to induce expression of the blue fluorescence protein (BFP) gene. Fluorescence microscopy revealed that two types of fluorescence were emitted; one by soluble BFP and the other by aggregated BFP. As a result, the parameters that influence the formation of inclusion bodies can be examined by observing the fluorescence emitted by BFP, in real-time, with a fluorescence microscope. It was found that the aggregated BFP decreased with decreasing cultivation temperature, and the formation of inclusion bodies increased with decreased pH and increased IPTG concentrations. In addition, the aggregated form of BFP emitted fluorescence, indicating that BFP inclusion bodies might remain, at least partially, in a properly folded native-like form.

High throughput purification of recombinant human growth hormone using radial flow chromatography

Recombinant human growth hormone (r-hGH) was expressed in Escherichia coli as inclusion bodies. Using fed-batch fermentation process, around 670 mg/L of r-hGH was produced at a cell OD600 of 35. Cell lysis followed by detergent washing resulted in semi-purified inclusion bodies with more than 80% purity. Purified inclusion bodies were homogenous in preparation having an average size of 0.6 microm. Inclusion bodies were solubilized at pH 12 in presence of 2M urea and refolded by pulsatile dilution. Refolded protein was purified with DEAE-anion exchange chromatography using both radial and axial flow column (50 ml bed volume each). Higher buffer flow rate (30 ml/min) in radial flow column helped in reducing the batch processing time for purification of refolded r-hGH. Radial column based purification resulted in high throughput recovery of diluted refolded r-hGH in comparison to axial column. More than 40% of inclusion body protein could be refolded into bioactive form using the above method in a single batch. Purified r-hGH was analyzed by mass spectroscopy and found to be bioactive by Nb2 cell line proliferation assay. Inclusion body enrichment, mild solubilization, pulsatile refolding and radial flow chromatography worked co-operatively to improve the overall recovery of bioactive protein from inclusion bodies.

Production enhancement and refolding of caprine growth hormone expressed in Escherichia coli

This study describes comparison between IPTG and lactose induction on expression of caprine growth hormone (cGH), enhancing cell densities of Escherichia coli cultures and refolding the recombinant cGH, produced as inclusion bodies, to biologically active state. 2-3 times higher cell densities were obtained in shake flask cultures when induction was done with lactose showing almost same level of expression as in case of IPTG induction. With lactose induction highest cell densities were achieved in TB (OD(600) 16.3) and M9NG (OD(600) 16.1) media, producing 885 and 892 mg cGH per liter of the culture, respectively. Lactose induction done at mid-exponential stage resulted in a higher cell density and thus higher product yield. cGH over-expressed as inclusion bodies was solubilized in 50 mM Tris-Cl buffer (pH 12.5) containing 2 M urea, followed by dilution and lowering the pH in a step-wise manner to obtain the final solution in 50mM Tris-Cl (pH 9.5). The cGH was purified by Q-Sepharose chromatography followed by gel filtration with a recovery yield of 39% on the basis of total cell proteins. The product thus obtained showed a single band by SDS-PAGE analysis. MALDI-TOF analysis showed a single peak with a mass of 21,851 dalton, which is very close to its calculated molecular weight. A bioassay based on proliferation of Nb2 rat lymphoma cells showed that the purified cGH was biologically active.

A strategic crossflow filtration methodology for the initial purification of promegapoietin from inclusion bodies

A novel crossflow filtration methodology is demonstrated for the initial purification of the therapeutic protein, promegapoietin-1a (PMP), produced as inclusion bodies (IBs) in a recombinant Escherichia coli bioprocess. Two strategic separation steps were performed by utilizing a filtration unit with a 1000 kDa polyethersulphone membrane. The first step, aiming for separation of soluble contaminants, resulted in a 50% reduction of the host cell proteins, quantified by total amino acid analysis and a 70% reduction of all DNA, quantified by fluorometry, when washing the particulate material with a 10mM EDTA in 50mM phosphate buffer, pH 8. The second step, aiming for separation of particulate contaminants from solubilized IBs, resulted in a 97-99.5% reduction of endotoxin, used as a marker for cell debris, and was quantified by the kinetic turbidimetric LAL endotoxin assay. The overall PMP yield was 58% and 33% respectively for the two solubilizations investigated, guanidine hydrochloride and arginine, as measured by RP-HPLC. The scope was also to investigate the physical characteristics of the intermediate product/s with regard to the choice of IB solvent. Preliminary results from circular dichroism spectroscopy measurements indicate that the protein secondary structure was restored when arginine was used in the second step.

Impact of different cultivation and induction regimes on the structure of cytosolic inclusion bodies of TEM1-beta-lactamase

The enzyme TEM1-beta-lactamase has been used as a model to study the impact of different cultivation and induction regimes on the structure of cytosolic inclusion bodies (IBs). The protein has been heterologously expressed in Escherichia coli in fed-batch cultivations at different temperatures (30, 37, and 40 degrees C) as well as induction regimes that guaranteed distinct product formation rates and ratios of soluble to aggregated protein. Additionally, shake flask cultivations at 20, 30, and 37 degrees C were performed. IBs were sampled during the whole bioprocess and structural analysis was performed by attenuated total reflectance Fourier transform infrared (ATR-FT-IR) spectroscopy. This work clearly demonstrates that the tested production regimes and rates had no impact on the IB structure, which was characterized by decreased alpha-helical and increased and modified beta-sheet contents compared to the native protein. Moreover, aggregates formed during refolding of IBs by solubilization and simple dilution showed very similar FT-IR spectra suggesting (i) the existence of only one critical folding step from which either aggregation (IB formation) or native folding branches off, and (ii) underlining the important role of the specific amino acid sequence in aggregation. The findings are discussed with respect to the known structure of TEM1-beta-lactamase and the reported kinetics of its (un)folding as well as contradictory data on the effect of cultivation regimes on IB structure(s) of other proteins.

Single step intein-mediated purification of hGMCSF expressed in salt-inducible E. coli

Human granulocyte-macrophage colony stimulating factor (hGMCSF) is an important therapeutic cytokine. As a novel attempt to purify hGMCSF protein, without the enzymatic cleavage of the affinity tag, an intein-based system was used. The gene was fused by overlap extension PCR to the intein sequence at its N-terminal in pTYB11 vector. The hGMCSF was expressed as a fusion protein in E. coli BL21(DE3), and E. coli GJ1158. In the former, the protein was expressed as inclusion bodies and upon purification the yield was 7 mg/l with a specific activity of 0.5 x 10(7) IU/mg. In salt-inducible E. coli GJ1158, hGMCSF was expressed in a soluble form at 20 mg/l and a specific activity of 0.9 x 10(7) IU/mg. The intein-hGMCSF was purified on a chitin affinity column by cleaving intein with 50 mM DTT resulting in a highly pure 14.7 kDa hGMCSF.

Size characterization of inclusion bodies by sedimentation field-flow fractionation

Sedimentation field-flow fractionation (sedFFF) was evaluated to characterize the size of Delta(4-23)TEM-beta-lactamase inclusion bodies (IBs) overexpressed in fed-batch cultivations of Escherichia coli. Heterologous Delta(4-23)TEM-beta-lactamase protein formed different sizes of IBs, depending upon the induction conditions. In the early phases of recombinant protein expression, induced with low concentrations of IPTG (isopropyl-beta-d-thiogalactoside), IB masses were larger than expected and showed heterogeneous size distributions. During cultivation, IB sizes showed a Gaussian distribution and reached a broad range by the end of the fed-batch cultivations. The obtained result proved the aptitude of sedFFF to rapidly assess the size distribution of IBs in a culture.

Solubilization and refolding with simultaneous purification of recombinant human stem cell factor

Recombinant human stem cell factor (rhSCF) was solubilized and renatured from inclusion bodies expressed in Escherichia coli. The effect of both pH and urea on the solubilization of rhSCF inclusion bodies was investigated; the results indicate that the solubilization of rhSCF inclusion bodies was significantly influenced by the pH of the solution employed, and low concentration of urea can drastically improve the solubilization of rhSCF when solubilized by high pH solution. The solubilized rhSCF can be easily refolded with simultaneous purification by ion exchange chromatography (IEC), with a specific activity of 7.8 x 10(5) IU x mg(-1), a purity of 96.3%, and a mass recovery of 43.0%. The presented experimental results show that rhSCF solubilized by high pH solution containing low concentration of urea is easier to be renatured than that solubilized by high concentration of urea, and the IEC refolding method was more efficient than dilution refolding and dialysis refolding for rhSCF. It may have a great potential for large-scale production of rhSCF.

Recombinant human epidermal growth factor inclusion body solubilization and refolding at large scale using expanded-bed adsorption chromatography from Escherichia coli

Amongst the various endogenous growth factors, epidermal growth factor (EGF) plays an important role in normal wound healing of tissue such as skin, cornea and gastrointestinal tract. Various studies have proved that supplementing recombinant human EGF (rhEGF) results in significant augmentation of wound healing. In the present work, a high level expression system with poly-arginine sequences was used for the production of recombinant human EGF (rhEGF) as inclusion bodies. The inclusion bodies were solubilized and the protein was refolded by using expanded-bed adsorption chromatography. The renatured protein was digested with appropriate concentration of trypsin and subsequently the digested rhEGF is purified by passing through ion-exchange chromatography (Toyopearl-SP) to obtain a biologically active protein. This process is the shortest process with reduced number of steps of purification, eliminates the usage of preparative reversed phase HPLC (RP-HPLC) for final purification, which is an expensive technique. The purified protein was analyzed by RP-HPLC, showing a purity > 99% and size exclusion chromatography profile shows that there are minimal aggregates, with 99% renatured active protein. The purified rhEGF showed a specific activity of 5 x 10(5) IU/mg protein, in comparison with NIBSC standard (1st International Standard of rDNA-derived EGF, Code 91/530). The process has been successfully adopted at 100 L fermentation scale and the rhEGF based formulation has been commercialized with brand name REGEN D, with excellent clinical results.

Effect of excipients on the encapsulation efficiency and release of human growth hormone from dextran microspheres

The possibility was investigated to modulate the encapsulation efficiency and release of human growth hormone (hGH) from hydroxyl ethyl methacrylated dextran (dex-HEMA) hydrogel microspheres by using excipients. Microspheres were prepared by polymerization of dex-HEMA in an aqueous two-phase system of this polymer and PEG with or without excipients (Tween 80, pluronic F68, sucrose, NaCl, urea or methionine). High hGH encapsulation efficiencies (50-70%) were obtained for microspheres prepared without excipients and with Tween 80, NaCl or methionine. Substantially lower encapsulation efficiencies (27% and 19%, respectively) were obtained for microspheres prepared in the presence of sucrose and urea, which was attributed to the more favoured partitioning of hGH over the PEG-phase due to higher hydrophobicity of the (partly) denatured hGH. Likely, differences in precipitate size of the encapsulated hGH resulted in different release profiles between microspheres prepared without excipients (biphasic release: 2 days delay time followed by 6 days release) and the release profile for microspheres prepared with Tween 80, pluronic F68, sucrose, NaCl and urea (release over a period of 6-8 days (without a delay time)). Microspheres prepared with methionine showed a concentration-dependent delay time varying from 0 to 2 days followed by almost zero-order release over 6 days, attributed to the effect of methionine on the polymerization of dex-HEMA. Especially, Tween 80 and methionine are attractive excipients since hGH was encapsulated in high yield (60-70%) and the protein was released from the microspheres mainly in its monomeric form without a delay time and with an almost zero-order release over 6-8 days.

Production of active eukaryotic proteins through bacterial expression systems: a review of the existing biotechnology strategies

Among the various expression systems employed for the over-production of proteins, bacteria still remains the favorite choice of a Protein Biochemist. However, even today, due to the lack of post-translational modification machinery in bacteria, recombinant eukaryotic protein production poses an immense challenge, which invariably leads to the production of biologically in-active protein in this host. A number of techniques are cited in the literature, which describe the conversion of inactive protein, expressed as an insoluble fraction, into a soluble and active form. Overall, we have divided these methods into three major groups: Group-I, where the factors influencing the formation of insoluble fraction are modified through a stringent control of the cellular milieu, thereby leading to the expression of recombinant protein as soluble moiety; Group-II, where protein is refolded from the inclusion bodies and thereby target protein modification is avoided; Group-III, where the target protein is engineered to achieve soluble expression through fusion protein technology. Even within the same family of proteins (e.g., tyrosine kinases), optimization of standard operating protocol (SOP) may still be required for each protein's over-production at a pilot-scale in Escherichia coli. However, once standardized, this procedure can be made amenable to the industrial production for that particular protein with minimum alterations.

Production of active eukaryotic proteins through bacterial expression systems: a review of the existing biotechnology strategies

Among the various expression systems employed for the over-production of proteins, bacteria still remains the favorite choice of a Protein Biochemist. However, even today, due to the lack of post-translational modification machinery in bacteria, recombinant eukaryotic protein production poses an immense challenge, which invariably leads to the production of biologically in-active protein in this host. A number of techniques are cited in the literature, which describe the conversion of inactive protein, expressed as an insoluble fraction, into a soluble and active form. Overall, we have divided these methods into three major groups: Group-I, where the factors influencing the formation of insoluble fraction are modified through a stringent control of the cellular milieu, thereby leading to the expression of recombinant protein as soluble moiety; Group-II, where protein is refolded from the inclusion bodies and thereby target protein modification is avoided; Group-III, where the target protein is engineered to achieve soluble expression through fusion protein technology. Even within the same family of proteins (e.g., tyrosine kinases), optimization of standard operating protocol (SOP) may still be required for each protein's over-production at a pilot-scale in Escherichia coli. However, once standardized, this procedure can be made amenable to the industrial production for that particular protein with minimum alterations.

ELISA com MSP5 recombinante truncada para detecção de anticorpos contra Anaplasma marginale em bovinos

Os objetivos deste estudo foram produzir e solubilizar a proteína MSP5 recombinante truncada de Anaplasma marginale, e avaliar seu desempenho em um ensaio de imunoadsorção enzimática indireto (ELISA) para detecção de anticorpos contra a riquétsia. O gene msp5, exceto a região N-terminal hidrofóbica, foi amplificado por PCR, clonado em plasmídeo pTrcHis-TOPO e expresso em Escherichia coli. A solubilização da proteína recombinante foi avaliada em diferentes pHs e concentrações de uréia. A sensibilidade e a especificidade do ensaio foram avaliados testando-se 66 soros de animais infectados experimentalmente com A. marginale e 96 soros negativos, com o estado de infecção destes animais confirmado por PCR. Um total de 1.666 amostras de soros bovino, provenientes do Brasil - Rio Grande do Sul (73), Mato Grosso do Sul (91), Pernambuco (86), Bahia (314) e Minas Gerais (267)-, Uruguai (32) e Costa Rica (803) foram testadas nos ELISAs com MSP5 truncada e com MSP1a recombinantes e a concordância entre os dois testes foi avaliada. O ELISA indireto com MSP5 truncada foi capaz de detectar animais infectados com 96,97% de sensibilidade e 100% de especificidade. Nos animais infectados experimentalmente, o ELISA detectou anticorpos do 12º até o último dia de observação (37º dia). Os ELISAs para MSP5 e MSP1a apresentaram concordância de 95,67%, com índice kappa de 0,81. Os resultados discordantes apresentaram uma diferença significativa (p <0,001). Anticorpos contra A. marginale foram detectados em animais de todas as regiões estudadas. O ELISA com MSP5 recombinante truncada apresentou bom desempenho na detecção de anticorpos contra A. marginale, com alta sensibilidade e especificidade, representando uma importante ferramenta para o diagnóstico da anaplasmose bovina em estudos epidemiológicos.

Efficient solubilization of inclusion bodies

The overexpression of recombinant proteins in Escherichia coli leads in most cases to their accumulation in the form of insoluble aggregates referred to as inclusion bodies (IBs). To obtain an active product, the IBs must be solubilized and thereafter the soluble monomeric protein needs to be refolded. In this work we studied the solubilization behavior of a model-protein expressed as IBs at high protein concentrations, using a statistically designed experiment to determine which of the process parameters, or their interaction, have the greatest impact on the amount of soluble protein and the fraction of soluble monomer. The experimental methodology employed pointed out an optimum balance between maximum protein solubility and minimum fraction of soluble aggregates. The optimized conditions solubilized the IBs without the formation of insoluble aggregates; moreover, the fraction of soluble monomer was approximately 75% while the fraction of soluble aggregates was approximately 5%. Overall this approach guarantees a better use of the solubilization reagents, which brings an economical and technical benefit, at both large and lab scale and may be broadly applicable for the production of recombinant proteins.

Molecular cloning, characterization, and expression studies of water buffalo (Bubalus bubalis) somatotropin

Cloning, high-level expression, and characterization of the somatotropin (ST) gene of an indigenous Nili-Ravi breed of water buffalo Bubalus bubalis (BbST) are described. Coding, non-coding, and promoter regions of BbST were amplified and sequenced. Sequence analysis revealed several silent and two interesting point mutations on comparison with STs of other vertebrate species. One interesting variation in the BbST sequence was the replacement of a conserved glutamine residue by arginine. A plasmid was also constructed for the production of BbST in Escherichia coli BL21 (RIPL) CodonPlus, under the control of IPTG-inducible T7-lac promoter. High-level expression could be obtained by synthesizing a codon-optimized ST gene and expressing it in the form of inclusion bodies. The inclusion bodies represented over 20% of the E. coli cellular proteins. The biologically active conformation of purified BbST was confirmed by its efficient growth promoting activity in Nb2 cell proliferation assay. The expression system and purification strategy employed promise to be a useful approach to produce BbST for further use in structure-function studies and livestock industry.

Efficient solubilization, purification of recombinant extracellular α-amylase from pyrococcus furiosus expressed as inclusion bodies in Escherichia coli

The gene encoding the Pyrococcus furiosus extracellular alpha-amylase (PFA) was amplified by PCR from P. furiosus genomic DNA and was highly expressed in Escherichia coli BL21-Codon Plus (DE3)-RIL. The recombinant alpha-amylase was mainly expressed in the form of insoluble inclusion bodies. An improved purification method was established in this paper. The solubilization of the inclusion bodies was achieved by 90 degrees C treatment for 3 min in Britton-Robinson buffer at pH 10.5. The solubilized PFA was then diluted and subsequently purified by Phenyl Sepharose chromatography. The overall yield of the new purification method was about 58,000 U/g wet cells, which is higher than previously reported.

Effect of temperature on protein quality in bacterial inclusion bodies

Increasing evidence indicates that protein aggregation in bacteria does not necessarily imply loss of biological activity. Here, we have investigated the effect of growth-temperature on both the activity and stability of the inclusion bodies formed by a point-mutant of Abeta42 Alzheimer peptide, using green fluorescent protein as a reporter. The activity in the aggregates inversely correlates with the temperature. In contrast, inclusion bodies become more stable in front of chemical denaturation and proteolysis when temperature increases. Overall, the data herein open new perspectives in protein production, while suggesting a kinetic competition between protein folding and aggregation during recombinant protein expression.

Subcellular distribution of theEntamoeba histolytica140 kDa FN-binding molecule during host-parasite interaction

Entamoeba histolyticatrophozoites recovered from the host-parasite interface during abscess development obtain different stimuli compared with long-term cultured cells. In order to have a better understanding about the mechanisms in which the 140 kDa fibronectin (FN)-binding molecule (EhFNR) is involved during the invasive process, we decided to compare the regulation process of this molecule among long-term cultured trophozoites, FN-stimulated trophozoites, and trophozoites recently recovered from a liver abscess. A cDNA clone (5A) containing a fragment of theEhFNR that shows identity to the C-terminal region of the intermediate galactose lectin subunit Igl, was selected with a mAb (3C10). Identity ofEhFNR with Igl was confirmed by immunoprecipitation with 3C10 and EH3015 (against the Gal/GalNAc intermediate subunit) mAbs. The 3C10 mAb was used as a tool to explore the modulation of the amoebic receptor (EhFNR). Our results showed specific regulation of theEhFNR in FN-interacted amoebas, as well as in trophozoites recovered at different stages of abscess development. This regulation involved mobilization of the receptor molecule from internal vesicles to the plasma membrane. Therefore, we suggest that in the host-parasite interface, theEhFNR (Igl) plays an important role in the adhesion process during abscess development.

Antigenicity and immunogenicity of the N-terminal 33-kDa processing fragment of the Plasmodium falciparum merozoite surface protein 1, MSP1: implications for vaccine development

The Plasmodium falciparum merozoite surface protein 1 (MSP1), MSP1-42 and MSP1-19 are protective malaria vaccines. MSP1-42 is cleaved to form MSP1-33 and MSP1-19. The role of MSP1-33 in immunity is unclear. We investigated the antibody responses to MSP1-33; and to MSP1-33Trunc, in which major conserved sequences were excised. While anti-MSP1-33 antibodies were subdominant in the anti-MSP1-42 responses, immunizations with MSP1-33 or MSP1-33Trunc induced high levels of antibodies reactive with MSP1-42 or whole merozoites. Anti-MSP1-33 and anti-MSP1-33Tunc antibodies crossreacted with both allelic forms of MSP1-42. Anti-MSP1-33 sera were ineffective in inhibiting parasite growth in vitro; but they significantly enhanced the activities of sub-optimal concentrations of the inhibitory anti-MSP1-42 sera. Thus, immunization strategies with MSP1-based vaccines may benefit from co-induction of anti-MSP1-33 responses to enhance efficacy and potency.

Purification and characterization of the second Streptomyces phospholipase A2 refolded from an inclusion body

A secreted phospholipase A(2) (PLA(2)) from Streptomyces violaceoruber A-2688, previously identified by us, is the first PLA(2) identified in prokaryotes. Genome sequence data of Streptomyces coelicolor A3(2) indicates that the bacterium carries two genes encoding hypothetical PLA(2)s, which exhibit 100 and 78% identity, respectively, to the S. violaceoruber PLA(2). In this study, we named the former and latter proteins as the first and second PLA(2)s, respectively. When the second PLA(2) was expressed in Escherichia coli cells, it formed an inclusion body. The present study demonstrates a method to purify it to homogeneity without the disappearance of the enzymatic activity: the inclusion body was washed with sodium deoxycholate and dissolved in the presence of 2 M urea at pH 12, then refolded by the dilution method. The refolding of enzyme was confirmed by the circular dichroism spectrum. The second PLA(2) purified to homogeneity had the same specific activity as that of the S. violaceoruber PLA(2) and the yield was approximately 6.8 mg/L culture. The second PLA(2) exhibits similar enzymatic properties to the S. violaceoruber PLA(2), except that the former enzyme does not utilize phophatidic acid as a substrate. The surface electrostatic potential of the S. coelicolor PLA(2) model, which is created by the computer-homology modeling, suggests that the positively charged surface of the enzyme does not affect the substrate specificity.

Construction of a protease-deficient strain set for the fission yeast Schizosaccharomyces pombe, useful for effective production of protease-sensitive heterologous proteins

One of the major problems hindering effective production and purification of heterologous proteins from the fission yeast Schizosaccharomyces pombe is proteolytic degradation of the recombinant gene products by host-specific proteases. As an initial solution to this problem, we constructed a protease-deficient disruptant set by respective disruption of 52 Sz. pombe protease genes. Functional screening of the resultant set was performed by observing secretory production of a proteolytically sensitive model protein, human growth hormone (hGH). The results indicated that some of the resultant disruptants were effective in reducing hGH degradation, as observed during the hGH expression procedure and mainly as a result of unknown serine- and/or cysteine-type proteases in the culture medium. These findings also demonstrated that construction of a protease-deficient strain set is not only useful for practical application in protein production, but also for functional screening, specification and modification of proteases in Sz. pombe, where further investigations of proteolytic processes and improvement through multiple gene manipulations are required.

Structural analysis of protein inclusion bodies by Fourier transform infrared microspectroscopy

The expression of recombinant human growth hormone (h-GH) and human interferon-alpha-2b (IFN-alpha-2b) in E. coli leads to the formation of insoluble protein aggregates or inclusion bodies (IBs). The secondary structure of these IBs, their corresponding native forms and thermal aggregates were studied by Fourier Transform Infrared (FT-IR) spectroscopy and microspectroscopy. It was demonstrated that residual native-like structures were maintained within IBs at different extents depending on the level of expression, with possible implications in biotechnology. Furthermore, comparison between infrared spectra of thermal aggregates and IBs suggests new insights on the structure of protein aggregates.

Molecular cloning, expression and immunological characterization of pejerrey (Odontesthes bonariensis) growth hormone

Growth hormone is an essential polypeptide required for normal growth and development of vertebrates. The pejerrey fish, Odontesthes bonariensis, is a South American atherinid freshwater fish considered as a promising species for aquaculture. Although growth hormone has been characterized in a number of fish, there are no published data on the structure of this hormone in atherinids, except that of a related species Odontesthes argentinensis. In this paper, the molecular cloning, expression and immunological characterization of pejerrey growth hormone (pjGH) is described. The predicted amino acid sequence of pjGH cDNA consisted of 204 amino acid residues with an estimated molecular mass of 23 kDa. Amino acid sequence was highly conserved among the two Atheriniformes where the growth hormone sequences are known (99% aa identity), highly to moderately conserve (75-92% aa identity) when compared to the other members of Acantopterigii superorder and clearly less conserved (49-66% identity) when compared to Salmoniformes (Protacanthopterygii), Cypriniformes and Siluriformes (Ostariophysi). A phylogenetic tree depicting the relationship of various teleost GH nucleotide sequences was inferred. Pejerrey GH was produced using recombinant DNA technology in a bacterial system, representing the first time an atherinid growth hormone protein was expressed as a recombinant protein in Escherichia coli. A specific antiserum of this hormone was raised in rabbits and its specificity tested by using Western blot and immunocytochemistry. The distribution of pjGH mRNA was also studied by RT-PCR and Southern blot analysis. The transcript was detected not only in the pituitary gland but also in the testis.

Solubilization and refolding of bacterial inclusion body proteins

Inclusion bodies produced in Escherichia coli are composed of densely packed denatured protein molecules in the form of particles. Refolding of inclusion body proteins into bioactive forms is cumbersome, results in poor recovery and accounts for the major cost in production of recombinant proteins from E. coli. With new information available on the structure and function of protein aggregates in bacterial inclusion bodies, it has been possible to develop improved solubilization and refolding procedures for higher recovery of bioactive protein. Inclusion bodies are formed from partially folded protein intermediates and are composed of aggregates of mostly single types of polypeptide. This helps to isolate and purify the protein aggregates to homogeneity before solubilization and refolding. Proteins inside inclusion body aggregates have native-like secondary structures. It is assumed that restoration of this native-like secondary structure using mild solubilization conditions will help in improved recovery of bioactive protein in comparison to solubilization using a high concentration of chaotropic agent. Analysis of the dominant forces causing aggregation during inclusion body formation provides information to develop suitable mild solubilization procedures for inclusion body proteins. Refolding from such solubilized protein will be very high due to restoration of native-like secondary structure. Human growth hormone inclusion bodies were purified to homogeneity from E. coli cells before solubilization and refolding. Pure inclusion bodies were solubilized at alkaline pH in the presence of 2 M urea solution. The solubilized proteins were refolded using a pulsatile renaturation process and subsequently purified using chromatographic procedures. More than 40% of the inclusion body proteins could be refolded back to the bioactive native conformation. Mild solubilization is thus the key for high recovery of bioactive protein from inclusion bodies.

Stabilizing Peptide Fusion for Solving the Stability and Solubility Problems of Therapeutic Proteins

PURPOSE

Protein aggregation is a major stability problem of therapeutic proteins. We investigated whether a novel stabilizing peptide [acidic tail of synuclein (ATS) peptide] could be generally used to make a more stable and soluble form of therapeutic proteins, particularly those having solubility or aggregation problems.

METHODS

We produced ATS fusion proteins by fusing the stabilizing peptide to three representative therapeutic proteins, and then compared the stress-induced aggregation profiles, thermostability, and solubility of them. We also compared the in vivo stability of these ATS fusion proteins by studying their pharmacokinetics in rats.

RESULTS

The human growth hormone-ATS (hGH-ATS) and granulocyte colony-stimulating factor-ATS (G-CSF-ATS) fusion proteins were fully functional as determined by cell proliferation assay, and the ATS fusion proteins seemed to be very resistant to agitation, freeze/thaw, and heat stresses. The introduction of the ATS peptide significantly increased the storage and thermal stabilities of hGH and G-CSF. The human leptin-ATS fusion protein also seemed to be very resistant to aggregation induced by agitation, freeze/thaw, and heat stresses. Furthermore, the ATS peptide greatly increased the solubility of the fusion proteins. Finally, pharmacokinetic studies in rats revealed that the ATS fusion proteins are also more stable in vivo.

CONCLUSION

Our data demonstrate that a more stable and soluble form of therapeutic proteins can be produced by fusing the ATS peptide.

Refolding and purification of non-fusion HPT protein expressed in Escherichia coli as inclusion bodies

The gene encoding hygromycin B phosphotransferase (hpt) is a widely used selectable marker in the production of genetically engineered crops. To facilitate the safety assessment of this protein, the non-fusion hpt expression plasmid was constructed and introduced into Escherichia coli to produce enough quantity of the HPT protein. High level expressed HPT was achieved but most of the expressed protein aggregated as inclusion bodies. The inclusion bodies were washed, separated from the cells, and solubilized by 0.3% Sarkosyl. The protein was renatured by dilution and dialysis, and then purified by anion-exchange chromatography. The activity is 8 U/mg protein and the purity is about 95%. Further studies showed that the microbially produced HPT protein had comparable molecular weight, immuno-reactivities, N-terminal amino acid sequences, and biological activities with those of the HPT produced by transgenic rice harboring hpt gene. All these results demonstrated the validity of utilizing the microbially produced HPT to assess the safety of the HPT protein produced in genetically engineered rice.

High-throughput automated refolding screening of inclusion bodies

One of the main stumbling blocks encountered when attempting to express foreign proteins in Escherichia coli is the occurrence of amorphous aggregates of misfolded proteins, called inclusion bodies (IB). Developing efficient protein native structure recovery procedures based on IB refolding is therefore an important challenge. Unfortunately, there is no "universal" refolding buffer: Experience shows that refolding buffer composition varies from one protein to another. In addition, the methods developed so far for finding a suitable refolding buffer suffer from a number of weaknesses. These include the small number of refolding formulations, which often leads to negative results, solubility assays incompatible with high-throughput, and experiment formatting not suitable for automation. To overcome these problems, it was proposed in the present study to address some of these limitations. This resulted in the first completely automated IB refolding screening procedure to be developed using a 96-well format. The 96 refolding buffers were obtained using a fractional factorial approach. The screening procedure is potentially applicable to any nonmembrane protein, and was validated with 24 proteins in the framework of two Structural Genomics projects. The tests used for this purpose included the use of quality control methods such as circular dichroism, dynamic light scattering, and crystallogenesis. Out of the 24 proteins, 17 remained soluble in at least one of the 96 refolding buffers, 15 passed large-scale purification tests, and five gave crystals.

Efficient refolding of aggregation-prone citrate synthase by polyol osmolytes: how well are protein folding and stability aspects coupled?

Efficient refolding of proteins and prevention of their aggregation during folding are of vital importance in recombinant protein production and in finding cures for several diseases. We have used citrate synthase (CS) as a model to understand the mechanism of aggregation during refolding and its prevention using several known structure-stabilizing cosolvent additives of the polyol series. Interestingly, no parallel correlation between the folding effect and the general stabilizing effect exerted by polyols was observed. Although increasing concentrations of polyols increased protein stability in general, the refolding yields for CS decreased at higher polyol concentrations, with erythritol reducing the folding yields at all concentrations tested. Among the various polyols used, glycerol was the most effective in enhancing the CS refolding yield, and a complete recovery of enzymatic activity was obtained at 7 m glycerol and 10 mug/ml protein, a result superior to the action of the molecular chaperones GroEL and GroES in vitro. A good correlation between the refolding yields and the suppression of protein aggregation by glycerol was observed, with no aggregation detected at 7 m. The polyols prevented the aggregation of CS depending on the number of hydroxyl groups in them. Stopped-flow fluorescence kinetics experiments suggested that polyols, including glycerol, act very early in the refolding process, as no fast and slow phases were detectable. The results conclusively demonstrate that both the thermodynamic and kinetic aspects are critical in the folding process and that all structure-stabilizing molecules need not always help in productive folding to the native state. These findings are important for the rational design of small molecules for efficient refolding of various aggregation-prone proteins of commercial and medical relevance.

Expression of an immunologically reactive merozoite surface protein (MSP-1(42)) in E. coli

The 42-kDa carboxyl-terminal processing fragment of Plasmodium falciparum merozoite surface protein-1 (PfMSP-1(42)) is one of the anti-malarial vaccine candidate antigens. In the present study, recombinant MSP-1(42) was expressed as a fusion protein in a novel E. coli host. The average yield of the recombinant protein was 48 mg/l of bacterial culture. The antigenicity and immunogenicity of the purified protein were evaluated by comparing the results with those obtained from a well-characterized recombinant MSP-1(42) (Bmp42) expressed in the baculovirus expression system previously described from our laboratory. We observed that there is a high degree of similarities between the two recombinant proteins. Based on the results from T and B cell response, in vitro parasite growth inhibition, as well as cross-reactivities with several well-characterized MSP-1 specific Mabs, the bacterial expressed protein is apparently comparable to Bmp42 in terms of immunoreactivities. Our results suggest that the bacterial expression system could be employed to express immunologically active recombinant MSP-1(42) at elevated levels. This system may be an attractive alternative for producing a protective vaccine for human use at lower cost.

Strategies for the recovery of active proteins through refolding of bacterial inclusion body proteins

Recent advances in generating active proteins through refolding of bacterial inclusion body proteins are summarized in conjunction with a short overview on inclusion body isolation and solubilization procedures. In particular, the pros and cons of well-established robust refolding techniques such as direct dilution as well as less common ones such as diafiltration or chromatographic processes including size exclusion chromatography, matrix- or affinity-based techniques and hydrophobic interaction chromatography are discussed. Moreover, the effect of physical variables (temperature and pressure) as well as the presence of buffer additives on the refolding process is elucidated. In particular, the impact of protein stabilizing or destabilizing low- and high-molecular weight additives as well as micellar and liposomal systems on protein refolding is illustrated. Also, techniques mimicking the principles encountered during in vivo folding such as processes based on natural and artificial chaperones and propeptide-assisted protein refolding are presented. Moreover, the special requirements for the generation of disulfide bonded proteins and the specific problems and solutions, which arise during process integration are discussed. Finally, the different strategies are examined regarding their applicability for large-scale production processes or high-throughput screening procedures.