Cosolvent Assisted Protein Refolding

Enhancing the crystallisation of insulin using amino acids as soft-templates to control nucleation

Amino acid as soft templates in promoting nucleation of insulin.

Potential application of waste from castor bean (Ricinus communis L.) for production for xylanase of interest in the industry

Xylanases activity (XY) from Aspergillus japonicus URM5620 produced by Solid-State Fermentation (SSF) of castor press cake (Ricinus communis) on different conditions of production and extraction by PEG/citrate aqueous two-phase system (ATPS) were investigated. XY production was influenced by substrate amount (5–10 g), initial moisture (15–35 %), pH (4.0–6.0) and temperature (25–35 °C), obtaining the maximum activity of 29,085 ± 1808 U g ds⁻¹ using 5.0 g of substrate with initial moisture of 15 % at 25 °C and pH 6.0, after 120 h of fermentation. The influence of PEG molar mass (1000–8000 g mol⁻¹), phase concentrations (PEG 20.0–24.0 % w/w and sodium citrate 15–20 % w/w) and pH (6.0–8.0) on partition coefficient, purification factor, yield and selectivity of XY were determinate. Enzyme partitioning into the PEG rich phase was favored by M_PEG 8000 (g mol⁻¹), C_PEG 24 % (w/w), C_C 20 % (w/w) and pH 8.0, resulting in partition coefficient of 50.78, activity yield of 268 %, 7.20-fold purification factor and selectivity of 293. A. japonicus URM5620 has a potential role in the development of a bioprocess for the XY production using low-cost media. In addition, the present study proved it is feasible to extract xylanase from SSF by adopting the one step ATPS consisting of PEG/citrate.

Nano-cage-mediated refolding of insulin by PEG-PE micelle

Insulin aggregation has pronounced pharmaceutical implications and biological importance. Deposition of insulin aggregates is associated with type II diabetes and instability of pharmaceutical formulations. We present in this study the renaturation effect of PEG-PE micelle on dithiothreitol (DTT)-denatured insulin revealed by techniques including turbidity assay, circular dichroism (CD), thioflavinT (ThT) binding assay, bis-ANS binding assay, agarose gel electrophoresis and MALDI-TOF MS. The obtained results show that PEG-PE micelle having a hydrophilic nano-cage-like structure in which with a negative charge layer, can capture DTT-induced insulin A and B chains, and block their hydrophobic interaction, thereby preventing aggregation. The reduced insulin A and B chain in the nano-cage are capable of recognizing each other and form the native insulin with yields of ∼30% as measured by hypoglycemic activity analysis in mice. The observed insulin refolding assisted by PEG-PE micelle may be applicable to other proteins.

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.

PEGylation-aided refolding of globular adiponectin

Globular adiponectin (GAD) as the active domain of adiponectin is a promising candidate for anti-diabetic drug development. The recombinant production of GAD in Escherichia coli, however, is difficult because it is mainly expressed as inclusion bodies which need to be refolded to regain function. In this study we developed a novel method for refolding of GAD with a high efficiency by using polyethylene glycol (PEG) conjugation. An artificially designed DNA sequence encoding for GAD was synthesized and inserted into the pET28a vector to construct an expression plasmid which was thereafter transformed into E. coli BL21 (DE3) host cells for heterologous expression. After bacterial cell culture employing auto-induction medium, the inclusion bodies were collected, washed and dissolved in guanidine hydrochloride before PEG conjugation. Then the PEG-conjugated GAD was refolded by dialysis and purified by two steps of chromatography. The refolded conjugate showed a marked glucose-lowering activity in mice, demonstrating that it had been successfully refolded. As a convenient method, PEGylation-aided refolding could also be tested on other proteins to explore its suitability.

Chemical assistance in refolding of bacterial inclusion bodies

Escherichia coli is one of the most widely used hosts for the production of recombinant proteins but insoluble expression of heterologous proteins is a major bottleneck in production of recombinant proteins in E. coli. In vitro refolding of inclusion body into proteins with native conformations is a solution for this problem but there is a need for optimization of condition for each protein specifically. Several approaches have been described for in vitro refolding; most of them involve the use of additives for assisting correct folding. Cosolutes play a major role in refolding process and can be classified according to their function as aggregation suppressors and folding enhancers. This paper presents a review of additives that are used in refolding process of insoluble recombinant proteins in small scale and industrial processes.

Stabilization of proteins for storage

Following isolation and purification, it is often necessary to store proteins and peptides for extended periods of time before performing detailed biophysical, enzymatic, and structural proteomics. Therefore, it is essential that the pure target protein maintain its original biological (or functional) behavior over an extended period of storage which may range from weeks to years. Protein pharmaceuticals must remain viable following extensive shipping and storage, and they must remain devoid of all possible inactivation processes. The shelf life of a protein depends on both the intrinsic nature of the protein and the storage conditions. Proteins (especially enzymes) must be stored at an appropriate temperature and pH range and frequently in the presence of concentrated (approximately 1 M) glycerol, sucrose, or a similar substance, for the proteins to retain activity and prevent aggregation. This article discusses the major causes of protein inactivation and describes a range of measures that can be adopted to maintain the stability and solubility of proteins.

Development of a rapid, high-efficiency, scalable refold for neurotrophin-4

A scalable refold for human neurotrophin-4 was developed as part of a manufacturing process required for the production of supplies for preclinical and clinical studies. The process redox system, chaotrope, solubilization additives, pH, temperature and protein concentration were optimized. The limited availability of suitable material for experimentation during concurrent downstream process development led to the approach described in the present paper: a combination of OFAT (one factor at a time) and multivariate DOE (design of experiments) to identify appropriate conditions. The optimized refold conditions included the use of sulfonated protein, raw materials utilized in other process operations and an inexpensive redox system. The conditions were found to be robust and were demonstrated from the millilitre scale to the 300 litre pilot scale. A process control procedure that utilized an RPC (reversed-phase chromatography) quantitative assay to monitor the percentage conversion into oxidized protein was developed. Refold conversions of 80-90% were obtained under ambient temperature and atmospheric conditions, with reaction times of approx. 18 h.

Use of zeolite to refold a disulfide-bonded protein

Zeolites are microporous crystalline aluminosilicates with a highly ordered structure. Using zeolite beta as an adsorbent, denatured/reduced hen egg lysozyme was refolded to the active form at high concentrations. The denatured/reduced lysozyme was adsorbed onto the zeolite and the protein was refolded by desorbing it into refolding buffer, consisting of redox reagents, guanidine hydrochloride, polyethylene glycol, and L-arginine. This zeolite refolding method could be highly effective for various kinds of proteins, refolding them with high efficiency even when they contain disulfide bonds.

Confronting high-throughput protein refolding using high pressure and solution screens

Over-expression of heterologous proteins in Escherichia coli is commonly hindered by the formation of inclusion bodies. Nevertheless, refolding of proteins in vitro has become an essential requirement in the development of structural genomics (proteomics) and as a means of recovering functional proteins from inclusion bodies. Many distinct methods for protein refolding are now in use. However, regardless of method used, developing a reliable protein refolding protocol still requires significant optimization through trial and error. Many proteins fall into the category of "Challenging" or "Difficult to Express" and are problematic to refold using traditional chaotrope-based refolding techniques. This review discusses new methods for improving protein refolding, such as implementing high hydrostatic pressure, using small molecule additives to enhance traditional protein refolding strategies, as well as developing practical methods for performing refolding studies to maximize their reliability and utility. The strategies examined here focus on high-throughput, automated refolding screens, which can be applied to structural genomic projects.

Molecular simulation of polymer assisted protein refolding

Protein refolding in vitro, the formation of the tertiary structure that enables the protein to display its biological function, can be significantly enhanced by adding a polymer of an appropriate hydrophobicity and concentration into the refolding buffer. A molecular simulation of the refolding of a two-dimensional simple lattice protein was presented. A protein folding map recording the occurrence frequency of specified conformations was derived, from which the refolding thermodynamics and kinetics were interpreted. It is shown that, in the absence of polymer, the protein falls into the "energy trapped" conformations characterized by a high intramolecular hydrophobic interaction, denoted as HH contact, and a high magnitude of the structure overlap function, chi. This makes it difficult for the protein to fold to the native state. The polymer with a suitable chain length, concentration, and hydrophobicity has formed complex with partially folded protein and created diversified intermediates with low chi. This gives more pathways for the protein to fold to the native state. At a given hydrophobicity, the short chain polymer has a broader concentration range where it assists protein folding than those of long chains. The above simulation agrees well with the experimental results reported elsewhere [Cleland et al., J. Biol. Chem. 267, 13327 (1992); ibid., Bio/Technology 10, 1013 (1992); Chen et al., Enzyme Microb. Technol. 32, 120 (2003); Lu et al., Biochem. Eng. J. 24, 55 (2005); ibid., J. Chem. Phys. 122, 134902 (2005); ibid., Biochem. Eng. J. (to be published)] and is of fundamental importance for the design and application of polymers for protein refolding.

l-Argininamide improves the refolding more effectively than l-arginine

L-arginine (Arg) is a widely used additive for suppressing protein aggregation during refolding. Systematic screening of Arg analogs provides superior additives that enhance the refolding yield more effectively than Arg. The refolding yield of hen egg lysozyme in the presence of 500 mM L-argininamide (ArgAd) increases 1.7-fold higher than Arg. Thermal unfolding experiments indicate that ArgAd has a greater denaturing effect than Arg. The refolding yield positively relates to the net charge of Arg analogs. Moreover ArgAd was also effective for the refolding of bovine carbonic anhydrase. High potency to increase the refolding yield of ArgAd compared to Arg results from high positive net charge and the denaturing property.

Optimizing refolding and recovery of active recombinant Bacillus halodurans xylanase in polymer–salt aqueous two-phase system using surface response analysis

An experimental design was used to determine optimal conditions for refolding of a recombinant thermostable and alkaline active xylanase from Bacillus halodurans in PEG-phosphate two-phase system. The influence of different experimental variables on the enzyme recovery has been evaluated. To build the mathematical model and minimize the number of experiments for the design parameters, response surface methodology with a face-centered central composite design (CCF) was defined based on the conditions found by preliminary tests that resulted in the highest refolding yield. The adequacy of the calculated model for the response was confirmed by means of variance analysis and additional experiments. Analysis of contours of constant response as a function of pH, polyethylene glycol (PEG) molecular weight and concentration, and salt concentration for different enzyme loads revealed different effects of these five factors on the studied parameters. Recovery of more than 92% active xylanase was predicted for a system with 18.3% (w/w) PEG 1000, 14.4% (w/w) phosphate at pH 8.5, and enzyme load corresponding to a protein concentration of about 0.05 mg/g system. The yield of the refolded enzyme was found to be optimal at 22 degrees C. The validity of the response model was verified by a good agreement between predicted and experimental results.

A newly proposed mechanism for arginine-assisted protein refolding--not inhibiting soluble oligomers although promoting a correct structure

Arginine has been demonstrated to be capable of suppressing aggregation during protein refolding. However, the pathway and the mechanism for arginine to participate in and to assist refolding process still remains unclear. In this study, arginine-assisted refolding of recombinant consensus interferon (rIFN-con1) was investigated. It was found that although arginine minimized the formation of protein precipitate, it failed to prevent the formation of the soluble oligomeric species. The amount of the oligomers increased with the increase in arginine concentration. This phenomenon has not been reported. On the other hand, arginine was able to promote the yield of correctly refolded rIFN-con1, which was more than 2 times higher than that in the absence of arginine. A proposed mechanism is the stabilization of different soluble species by arginine, which slowed down the conformational movement. The stabilization effect on native-like structure formation overwhelmed the oligomeric promotion effect, which resulted in a composite effect of increased refolding yield for rIFN-con1 when arginine concentration was below 0.5M.

Surfactant copolymers prevent aggregation of heat denatured lysozyme

We investigated the ability of certain triblock copolymer surfactant poloxamers of the form polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO), to prevent formation of stable aggregates of heat denatured hen egg lysozyme. Differential scanning calorimetry (DSC) and synchrotron small angle x-ray scattering (SAXS) experiments were performed to study the thermodynamics and solution structures of lysozyme at temperatures between 20 and 90 degrees C in the presence and absence of poloxamers with various molecular weights (8.4-14.3 kDa), but similar hydrophile/hydrophobe (PEO:PPO) ratio of 80%. Poloxmer 188 was found to be very effective in preventing aggregation of heat denatured lysozyme and those functioned as a synthetic surfactant, thus enabling them to refold when the conditions become optimal. For comparison, we measured the ability of 8 kDa polyethylene glycol (PEG) to prevent lysozyme aggregation under same conditions. The results of these studies suggest that poloxamers are more efficient than PEG in preventing aggregation of heat denaturated lysozyme. To achieve equivalence, more than an order of magnitude higher concentration of PEG concentration was needed. Apparently, the presence of a hydrophobic segment in the poloxamers increases their ability to target the hydrophobic region of the unfolded proteins and protect them from self association. Given their biocompatibility and the low concentrations at which they effectively facilitate refolding of denatured proteins, they may be useful in the treatment of burns and other conditions resulting in the denaturation of proteins.

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.

Bioprocessing of therapeutic proteins from the inclusion bodies of Escherichia coli

Escherichia coli has been most extensively used for the large-scale production of therapeutic proteins, which do not require complex glycosylation for bioactivity. In recent years tremendous progress has been made on the molecular biology, fermentation process development and protein refolding from inclusion bodies for efficient production of therapeutic proteins using E. coli. High cell density fermentation and high throughput purification of the recombinant protein from inclusion bodies of E. coli are the two major bottle necks for the cost effective production of therapeutic proteins. The aim of this review is to summarize the developments both in high cell density, high productive fermentation and inclusion body protein refolding processes using E. coli as an expression system. The first section deals with the problems of high cell density fermentation with an aim to high volumetric productivity of recombinant protein. Process engineering parameters during the expression of ovine growth hormone as inclusion body in E. coli were analyzed. Ovine growth hormone yield was improved from 60 mg L(-1) to 3.2 g L(-1) using fed-batch culture. Similar high volumetric yields were also achieved for human growth hormone and for recombinant bonnet monkey zona pellucida glycoprotein expressed as inclusion bodies in E. coli. The second section deals with purification and refolding of recombinant proteins from the inclusion bodies of E. coli. The nature of inclusion body protein, its characterization and isolation from E. coli has been discussed in detail. Different solubilization and refolding methods, which have been used to recover bioactive protein from inclusion bodies of E. coli have also been discussed. A novel inclusion body protein solubilization method, while retaining the existing native-like secondary structure of the protein and its subsequent refolding in to bioactive form, has been discussed. This inclusion body solubilization and refolding method has been applied to recover bioactive recombinant ovine growth hormone, recombinant human growth hormone and bonnet monkey zona pellucida glycoprotein from the inclusion bodies of E. coli.

Effect of column dimensions and flow rates on size-exclusion refolding of beta-lactamase

We have investigated the effect of changing the column diameter and length on the size exclusion chromatography (SEC) refolding of beta-lactamase from Escherichia coli-derived inclusion bodies (IBs). Inclusion bodies were recovered and solubilised in 6 M GdnHCl and 5 mM DTT. Up to 16 mg of denatured, solubilised beta-lactamase was loaded onto size exclusion columns packed with Sephacryl S-300 media (fractionation range: 10(4)-1.5 x 10(6) Da). beta-Lactamase was refolded by eluting the loaded sample with 1 M urea in 0.05 M phosphate buffer, pH 7 at 23 degrees C. The following columns were studied: 26 x 400, 16 x 400 and 26 x 200 mm, with a range of mobile phase flow rates from 0.33 to 4.00 ml/min. beta-Lactamase was successfully refolded in all three columns and at all flow rates studied. The beta-lactamase activity peak coincided with the major protein peak. Reducing the column diameter had little effect on refolding performance. The enzyme activity recovered was relatively independent of the mobile phase linear velocity. Reducing the column length gave a poorer resolution of the protein peaks, but the enzyme activity peaks were well resolved. Calculation of the partition coefficients for beta-lactamase activity showed that the 26 x 400 column gave the greatest refolding performance.

Practical considerations in refolding proteins from inclusion bodies

Refolding of proteins from inclusion bodies is affected by several factors, including solubilization of inclusion bodies by denaturants, removal of the denaturant, and assistance of refolding by small molecule additives. We will review key parameters associated with (1) conformation of the protein solubilized from inclusion bodies, (2) change in conformation and flexibility or solubility of proteins during refolding upon reduction of denaturant concentration, and (3) the effect of small molecule additives on refolding and aggregation of the proteins.

Alpha-crystallin and ATP facilitate the in vitro renaturation of xylanase: enhancement of refolding by metal ions

Alpha-crystallin is a multimeric protein that functions as a molecular chaperone and shares extensive structural homology to small heat shock proteins. For the functional in vitro analysis of alpha-crystallin, the xylanase Xyl II from alkalophilic thermophilic Bacillus was used as a model system. The mechanism of chaperone action of alpha-crystallin is less investigated. Here we studied the refolding of Gdn HCl-denatured Xyl II in the presence and absence of alpha-crystallin to elucidate the molecular mechanism of chaperone-mediated in vitro folding. Our results, based on intrinsic tryptophan fluorescence and hydrophobic fluorophore 8-anilino-1-naphthalene sulfonate binding studies, suggest that alpha-crystallin formed a complex with a putative molten globule-like intermediate in the refolding pathway of Xyl II. The alpha-crystallin.Xyl II complex exhibited no functional activity. Addition of ATP to the complex initiated the renaturation of Xyl II with 30%-35% recovery of activity. The nonhydrolyzable analog 5'-adenylyl imidodiphosphate (AMP-PNP) was capable of reconstitution of active Xyl II to a lesser extent than ATP. Although the presence of Ca(2+) was not required for the in vitro refolding of Xyl II, the renaturation yield was enhanced in its presence. Experimental evidence indicated that the binding of ATP to the alpha-crystallin.Xyl II complex brought about conformational changes in alpha-crystallin facilitating the dissociation of xylanase molecules. This is the first report of the enhancement of alpha-crystallin chaperone functions by metal ions.

Manipulation of unfolding-induced protein aggregation by peptides selected for aggregate-binding ability through phage display library screening

A phage-displayed library of peptides (12-mer) was screened for the ability to bind to thermally aggregated bovine carbonic anhydrase (BCA), with a view toward examining whether peptides possessing this ability might bind to partially structured intermediates on the protein's unfolding pathway and, therefore, constitute useful tools for manipulation of the kinetic partitioning of molecules between the unfolded and aggregated states. Two peptides [N-HPSTMGLRTMHP-C and N-TPSAWKTALVKA-C] were identified and tested. While neither showed thermal aggregation autonomously, both peptides individually elicited remarkable increases in the levels of thermal aggregation of BCA. A possible explanation is that both peptides bind to surfaces on molten BCA that are not directly involved in aggregation. Such binding could slow down interconversions between folded and unfolded states and stabilize aggregation-prone intermediate(s) to make them more prone to aggregation, while failing to achieve any steric prevention of aggregation. The approach has the potential of yielding useful aggregation-aiding/inhibiting agents, and may provide clues to whether amorphous aggregates are "immobilized" forms of folding intermediates.

C-terminal truncation of alpha 1,6-fucosyltransferase from Rhizobium sp. does not annul the transferase activity of the enzyme

Recently we have over-expressed the enzyme alpha 1,6-fucosyltransferase from Rhizobium sp. in Escherichia coli. In this heterologous system the enzyme was mainly expressed as inclusion bodies and the one that was expressed soluble showed a short-lasting activity in solution due to precipitation of the protein. A structural analysis of the sequence using the TMpred program predicted a highly hydrophobic region of 19 aa close to the C-terminal of the protein. In order to investigate the influence of this region on the formation of inclusion bodies and the precipitation from solution, we cloned a truncated version of the protein where a C-terminal fragment of 65 aa, including the predicted transmembrane-like region, was removed. The resulting protein was expressed in a soluble form without formation of inclusion bodies. The truncated protein catalyzed the transfer of a fucopyranosyl moiety from GDP-beta-L-Fucose to chitobiose. Comparison of the acceptor specificity between the truncated alpha 1,6-fucosyltransferase and the wild-type enzyme, showed a similar behavior for both enzymes. Our results indicate that the active center is not located in the C-terminal extreme of the protein in contrast to the case of the mammalian glycosyltransferases. Also, these results indicate that the alpha-6-motif III is not directly involved in the catalytic activity of the enzyme.

Protein renaturation by the liquid organic salt ethylammonium nitrate

The room-temperature liquid salt, ethylammonium nitrate (EAN), has been used to enhance the recovery of denatured-reduced hen egg white lysozyme (HEWL). Our results show that EAN has the ability to prevent aggregation of the denatured protein. The use of EAN as a refolding additive is advantageous because the renaturation is a one-step process. When HEWL was denatured reduced using routine procedures and renatured using EAN as an additive, HEWL was found to regain 75% of its activity. When HEWL was denatured and reduced in neat EAN, dilution resulted in over 90% recovery of active protein. An important aspect of this process is that renaturation of HEWL occurs at concentrations of 1.6 mg/mL, whereas other renaturation processes occur at significantly lower protein concentrations. Additionally, the refolded-active protein can be separated from the molten salt by simple desalting methods. Although the use of a low-temperature molten salt in protein renaturation is unconventional, the power of this approach lies in its simplicity and utility.

Role of protein-solvent interactions in refolding: effects of cosolvent additives on the renaturation of porcine pancreatic elastase at various pHs

The effects of cosolvent additives on the refolding of porcine pancreatic elastase were studied by comparing the enzymatic activity and the conformation of the enzyme renatured at various pHs with those of the native elastase under the same cosolvent and pH conditions. A lag period was observed before reaching the steady state of the hydrolysis of an amide substrate, and the lag period measured with the refolding enzyme was longer than that measured with the native elastase. Depending on the cosolvent studied (acetonitrile, dimethylsulfoxide, glycerol, methanol) there was or was not a dramatic increase in the duration of the lag period measured with the refolding enzyme, but not in the case of the native elastase. These results and additional kinetic data on inactivation of the enzyme demonstrated that dimethylsulfoxide, glycerol, and methanol enhance the stability of the intermediates able to refold into the native form, contrary to acetonitrile. In neither the case of the native enzyme nor that of the renatured enzyme, did the cosolvents modify the pK(app) of ionization of the amino acids that control enzymatic activity, indicating that they did not penetrate the core of the refolded elastase. Conversely, they shifted toward a more alkaline pH the structural transition of the native elastase, and the amplitude of the shift was comparable to that observed in bulk water with elastase whose Ser 195 has been acylated, suggesting that cosolvents stabilized the structure of the folded molecule by increasing its packing.

Opposite behavior of two isozymes when refolding in the presence of non-ionic detergents

GroEL has a greater affinity for the mitochondrial isozyme (mAAT) of aspartate aminotransferase than for its cytosolic counterpart (cAAT) (Mattingly JR Jr, Iriarte A, Martinez-Carrion M, 1995, J Biol Chem 270:1138-1148), two proteins that share a high degree of sequence similarity and an almost identical spatial structure. The effect of detergents on the refolding of these large, dimeric isozymes parallels this difference in behavior. The presence of non-ionic detergents such as Triton X-100 or lubrol at concentrations above their critical micelle concentration (CMC) interferes with reactivation of mAAT unfolded in guanidinium chloride but increases the yield of cAAT refolding at low temperatures. The inhibitory effect of detergents on the reactivation of mAAT decreases progressively as the addition of detergents is delayed after starting the refolding reaction. The rate of disappearance of the species with affinity for binding detergents coincides with the slowest of the two rate-limiting steps detected in the refolding pathway of mAAT. Limited proteolysis studies indicate that the overall structure of the detergent-bound mAAT resembles that of the protein in a complex with GroEL. The mAAT folding intermediates trapped in the presence of detergents can resume reactivation either upon dilution of the detergent below its CMC or by adding beta-cyclodextrin. Thus, isolation of otherwise transient productive folding intermediates for further characterization is possible through the use of detergents.

Artificial cell containing superoxide dismutase--selection of folding aids for stabilisation of SOD

Superoxide dismutase (abbreviated as SOD) has been vigorously studied in the fields of radical chemistry and related life science. One of practical problems is how to keep its activity in certain adverse conditions causing denaturation. Artificial cell containing SOD can be prepared by polymer encapsulation or nanocapsulation which has been found to be effective to improve the stability of SOD. For construction of an ideal artificial cell system, some folding aids or aggregation inhibitors were utilised to enhance SOD stability. In this study, three groups of biopolymers are selected as folding aids or aggregation inhibitors for stabilisation of SOD, i.e. albumin, carbohydrates and glycoproteins. Results indicate that the thermostability of SOD is affected by different sort of albumin while some carbohydrates such as cyclodextrins are found to be able to enhance SOD stability. In addition, it is firstly found that selected glycoproteins such as alpha-macroglobulin and ovalbumin are several types of effective folding aids for stabilisation of SOD. They can protect SOD against denaturation even at very high temperature(over 100 degrees C). The stability was tested by the measurement of SOD activity loss using autooxidation method in different adverse conditions such as high temperature, extreme pH medium, proteolytic hydrolysis and long shelf life storage. The possible stabilisation mechanism of using cyclodextrins and glycoproteins as folding aids were discussed.

Separation used for purification of recombinant proteins

The purification of molecules from recombinant cells may be strongly influenced by the molecular biology of gene isolation and expression. At the beginning of the process there may be a demand for information on the minute amounts of proteins and thus for ever increasingly sensitive techniques. Purification of recombinant proteins can differ from conventional purifications in several ways, depending on the solubility of the protein, occurrence in inclusion bodies, creation of fusion proteins with tags that enable simpler purification. Sometimes a (re)naturation step is required to get a bioactive protein. On the other hand, the techniques used in separation are essentially the same as for purification from the natural source and environment.

Studies of the hydrodynamic volume changes that occur during refolding of lysozyme using size-exclusion chromatography

A size-exclusion chromatography-based refolding process (SEPROS) has successfully been used to renature lysozyme at high concentrations. This process is based on the different hydrodynamic characteristics of folded and unfolded proteins and their interaction with gel filtration media. In this paper we have quantified the changes in Stokes radius, hydrodynamic volume and partition coefficient that occur when lysozyme is refolded from urea in a size-exclusion column. In 8 M urea partially folded and unfolded lysozyme were resolved using Superdex 75 HR. These two species were present at approximately the same concentration. As the urea concentration was decreased the unfolded species gradually decreased until at 4 M urea only partially folded lysozyme remained, which continued to fold on further reduction of the urea concentration. Using these results the initial mechanism for size exclusion chromatography protein refolding has been confirmed.