Refolding of reduced, denatured trypsinogen and trypsin immobilized on Agarose beads

Immobilized Horseradish Peroxidase on Enriched Diazo-Activated Silica Gel Harnessed High Biocatalytic Performance at a Steady State in Organic Solvent

Dimethyldichlorosilane (DMDCS), an efficient silane coupling reagent appearing between the -OH groups of silica gel (SG) and picric acid, instantaneously produces a derivative enriched with nitro groups. The nitro group acting as an end-cap terminates the reaction and subsequently was converted into diazo to couple tyrosine's phenol ring via its O-carbon, the inert center to immobilize horseradish peroxidase (HRP) in a multipoint mode. It maintains the status quo of the native enzyme's protein folding and the entire protein groups' chemistry. The molecular formula of the synthesized material was verified and appeared as {Si(OSi)4 (H2O)x}n{-O-Si(CH3)2-O-C6H2(N+≡N)3(HRP)}4·yH2O; the parameters were evaluated as x = 0.5, n = 1158, and y = 752. The immobilized biocatalyst's activity in organic solvents was 1.5 times better than that in an aqueous medium; it worked smoothly, wherein the activity in both solvents stabilized at six months and continued up to nine months at 63 ± 3% compared to the initial.

Degradation-Suppressed Cocoonase for Investigating the Propeptide-Mediated Activation Mechanism

Cocoonase is folded in the form of a zymogen precursor protein (prococoonase) with the assistance of the propeptide region. To investigate the role of the propeptide sequence on the disulfide-coupled folding of cocoonase and prococoonase, the amino acid residues at the degradation sites during the refolding and auto-processing reactions were determined by mass spectrometric analyses and were mutated to suppress the numerous degradation reactions that occur during the reactions. In addition, the Lys⁸ residue at the propeptide region was also mutated to estimate whether the entire sequence is absolutely required for the activation of cocoonase. Finally, a degradation-suppressed [K8D,K63G,K131G,K133A]-proCCN protein was prepared and was found to refold readily without significant degradation. The results of an enzyme assay using casein or Bz-Arg-OEt suggested that the mutations had no significant effect on either the enzyme activity or the protein conformation. Thus, we, herein, provide the non-degradative cocoonase protein to investigate the propeptide-mediated protein folding of the molecule. We also examined the catalytic residues using the degradation-suppressed cocoonase. The point mutations at the putative catalytic residues in cocoonase resulted in the loss of catalytic activity without any secondary structural changes, indicating that the mutated residues play a role in the catalytic activity of this enzyme.

Purification and Refolding of Overexpressed Human Basic Fibroblast Growth Factor in Escherichia coli

This work describes the integration of expanded bed adsorption (EBA) and adsorptive protein refolding operations used to recover purified and biologically active human basic fibroblast growth factor from inclusion bodies expressed in E. coli. Insoluble overexpressed human basic fibroblast growth factor has been purified on CM Hyper Z matrix by expanded bed adsorption after isolation and solubilization in 8 M urea. The adsorption was made in expanded bed without clarification steps such as centrifugation. Column refolding was done by elimination of urea and elution with NaCl. The human basic fibroblast growth factor was obtained as a highly purified soluble monomer form with similar behavior in circular dichroism and fluorescence spectroscopy as native protein. A total of 92.52% of the available human basic fibroblast growth factor was recovered as biologically active and purified protein using the mentioned purification and refolding process. This resulted in the first procedure describing high-throughput purification and refolding of human basic fibroblast growth factor in one step and is likely to have the greatest benefit for proteins that tend to aggregate when refolded by dilution.

Protein disulfide isomerase: a critical evaluation of its function in disulfide bond formation

Disulfide bond formation is probably involved in the biogenesis of approximately one third of human proteins. A central player in this essential process is protein disulfide isomerase or PDI. PDI was the first protein-folding catalyst reported. However, despite more than four decades of study, we still do not understand much about its physiological mechanisms of action. This review examines the published literature with a critical eye. This review aims to (a) provide background on the chemistry of disulfide bond formation and rearrangement, including the concept of reduction potential, before examining the structure of PDI; (b) detail the thiol-disulfide exchange reactions that are catalyzed by PDI in vitro, including a critical examination of the assays used to determine them; (c) examine oxidation and reduction of PDI in vivo, including not only the role of ERo1 but also an extensive assessment of the role of glutathione, as well as other systems, such as peroxide, dehydroascorbate, and a discussion of vitamin K-based systems; (d) consider the in vivo reactions of PDI and the determination and implications of the redox state of PDI in vivo; and (e) discuss other human and yeast PDI-family members.

Refolding of fully reduced bovine pancreatic trypsin

Refolding of bovine pancreatic trypsin was carried out. When starting with denatured S-S intact trypsin, the recovered activity attained was 95-100%. In contrast, the recovered activity after refolding denatured S-S reduced trypsin was considerably low compared with other proteases that have been worked with previously. Such low recovered activity was attributed to the small amount of fully reduced trypsin used as starting material for complete refolding. Taking this into account, a recovered activity of 86% could be achieved when using inhibitor-immobilized gels.

Disulfide formation as a probe of folding in GroEL-GroES reveals correct formation of long-range bonds and editing of incorrect short-range ones

The chaperonin GroEL assists protein folding by binding nonnative forms through exposed hydrophobic surfaces in an open ring and mediating productive folding in an encapsulated hydrophilic chamber formed when it binds GroES. Little is known about the topology of nonnative proteins during folding inside the GroEL-GroES cis chamber. Here, we have monitored topology employing disulfide bond formation of a secretory protein, trypsinogen (TG), that behaves in vitro as a stringent, GroEL-GroES-requiring substrate. Inside the long-lived cis chamber formed by SR1, a single-ring version of GroEL, complexed with GroES, we observed an ordered formation of disulfide bonds. First, short-range disulfides relative to the primary structure formed, both native and nonnative. Next, the two long-range native disulfides that "pin" the two beta-barrel domains together formed. Notably, no long-range nonnative bonds were ever observed, suggesting that a native-like long-range topology is favored. At both this time and later, however, the formation of several medium-range nonnative bonds mapping to one of the beta-barrels was observed, reflecting that the population of local nonnative structure can occur even within the cis cavity. Yet both these and the short-range nonnative bonds were ultimately "edited" to native, as evidenced by the nearly complete recovery of native TG. We conclude that folding in the GroEL-GroES cavity can favor the formation of a native-like topology, here involving the proper apposition of the two domains of TG; but it also involves an ATP-independent conformational "editing" of locally incorrect structures produced during the dwell time in the cis cavity.

Expression of human cationic trypsinogen with an authentic N terminus using intein-mediated splicing in aminopeptidase P deficient Escherichia coli

High-level expression of human trypsinogens as inclusion bodies in Escherichia coli requires deletion of the secretory signal sequence and placement of an initiator methionine at the N terminus. Trypsinogen preparations obtained this way contain a mixture of abnormal N termini, as a result of processing by cytoplasmic aminopeptidases. Here, we describe an expression system that produces recombinant human cationic trypsinogen with a native, intact N terminus, using intein-mediated protein splicing and an aminopeptidase P (pepP) deficient E. coli strain. As a first application of this system, the effect of the pancreatitis-associated mutation A16V on the autoactivation of human cationic trypsinogen was characterized. The use of the novel pepP knock-out E. coli strain should be generally applicable to the expression of recombinant proteins, which undergo unwanted N-terminal trimming by aminopeptidase P.

Purification, refolding, and characterization of recombinant Pseudomonas fluorescens lipase

Thermostable Pseudomonas fluorescens SIK W1 lipase (PFL), which is responsible for the spoilage of milk, was overexpressed as inclusion bodies in Escherichia coli. Renaturation of solubilized PFL was achieved by using size-exclusion protein refolding chromatography. The renatured enzyme was purified homogeneously using a combination of gel filtration and ion-exchange FPLC. Its specific activity was found to be enhanced in the presence of Ca2+. Secondary structural changes induced by Ca2+ were monitored by circular dichroism, which demonstrated that the activity increase of PFL in the presence of Ca2+ is strongly correlated with significant increases in alpha-helix and beta-sheet content. In the presence of Ca2+, the PFL structure was found resistant to denaturation by guanidine hydrochloride and to enzyme activity loss due to cosolvents like DMSO and trifluoroethanol, suggesting that Ca2+ plays an important role in inducing conformational changes and consequently in maintaining enzyme structural stability.

Chromatographic purification of an insoluble histidine tag recombinant Ykt6p SNARE from Arabidopsis thaliana over-expressed in E. coli

In order to undertake in plant cell the study of the endoplasmic reticulum (ER)-Golgi apparatus (GA) protein and/or lipid vesicular transport pathway, expressed sequence tag (EST) coding for a homologue to the yeast soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) Ykt6p has been cloned in Arabidopsis thaliana by reverse transcription polymerase chain reaction (RT-PCR). The corresponding protein was over-expressed as a recombinant histidine-tag (his-tag) protein in E. coli. Starting from one litter of culture, an ultrasonic homogenization was performed for cell disruption and after centrifugation the Arabidopsis Ykt6p SNARE present in inclusion bodies in the pellet was solubilized. After centrifugation, the clarified feedstock obtained was injected onto an immobilized metal affinity chromatography (IMAC) in presence of 6 M guanidine and on-column refolding was performed. Folded and subsequently purified (94% purity) recombinant protein was obtained with 82% of recovery.

In vitro protein refolding by chromatographic procedures

In vitro protein refolding is still a bottleneck in both structural biology and in the development of new biopharmaceuticals, especially for commercially important polypeptides that are overexpressed in Escherichia coli. This review focuses on protein refolding methods based on column procedures because recent advances in chromatographic refolding have shown promising results.

Effect of operating variables on the yield of recombinant trypsinogen for a pulse-fed dilution-refolding reactor

The inclusion body process route for manufacturing proteins offers distinct process advantages in terms of expression levels and the ease of initial inclusion body recovery. The efficiency of the refolding unit operation, however, does determine the overall economic feasibility of a process. Dilution refolding is the simplest and most extensively used refolding operation, although significant yield losses often occur due mainly to aggregation. Operating variables may have a significant effect on the degree of aggregation, but a systematic study has not been reported. This study investigates the effect of operating variables on the dilution refolding of solubilized r-trypsinogen inclusion bodies in a pulse-fed stirred reactor. Variables investigated were inclusion body washing, stirring speed, feed rate, concentration of solubilized r-trypsinogen, and concentration of urea during solubilization of the inclusion bodies. Additionally, the effect of baffles in the reactor was investigated. The yield of renatured r-trypsinogen varied between 12 +/- 0.2% and 21 +/- 1.0% depending on the specific combination of operating variables employed. It is clear that a suboptimal operating strategy can significantly reduce protein yield. In particular, we note that an increased intensity of mixing adversely affected yield in contrast to previous reports indicating that enhanced dispersion increases yield. We conclude that yield is determined not only by the efficiency of dispersion, but also by the local chemical environment of the protein as it folds, and the rate of change of this environment. This will be controlled by micromixing effects, and hence the intensity of agitation, in a complex manner requiring further characterization.

Observation of charge state and conformational change in immobilized protein using surface plasmon resonance sensor

Behaviors of proteins immobilized on a solid surface were investigated using BIACORE, a biosensor utilizing surface plasmon resonance. This sensor is usually used for analyzing binding events during biomolecular interactions. Here we propose a novel use of this sensor to monitor two kinds of intramolecular changes in immobilized proteins. Several proteins were covalently attached to dextran chains on the sensor surface in the flow cell and were then exposed to a series of buffers with varying pH. Signal changes derived from changes of refractive index around the sensor surface were detected during and after the exposure to each of these buffers, which we denoted as in situ values and postvalues, respectively. The in situ value reflects the behavior of immobilized proteins in these buffers and was revealed to have a correlation with total charge state of the proteins, while the postvalue reflects how immobilized proteins react after the exposure and was suggested to represent the degree of conformational changes of the proteins. This method is expected to be applicable to various analyses and can provide us with new information about the behavior of proteins on solid phase.

Urea gradient size-exclusion chromatography enhanced the yield of lysozyme refolding

Protein refolding is still a bottleneck for large-scale production of valuable proteins expressed as inclusion bodies in Escherichia coli. Usually biologically active proteins cannot be obtained with high yield at a high concentration after refolding. In order to meet the challenge of protein refolding a urea gradient gel filtration-refolding system was developed in this article. A Superdex 75 column was pre-equilibrated with a linear decreased urea gradient, the denatured protein experienced the gradual decrease in urea concentration as it went through the column. The refolding of denatured lysozyme showed this method could significantly increase the activity recovery of denatured lysozyme at high protein concentration. The activity recovery of 90% was obtained from the initial protein concentration up to 17 mg/ml within 40 min.

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.

Improved refolding of an immobilized fusion protein

Fusion proteins of monomeric alpha-glucosidase from Saccharomyces cerevisiae containing N- or C-terminal hexa-arginie peptides were expressed in the cytosol of Escherichia coli in soluble form. The polycationic peptide moieties allow noncovalent binding of the denatured fusion proteins to a polyanionic solid support. Upon removal of the denaturant, refolding of the matrix-bound protein can proceed without perturbation by aggregation. However, nonspecific interactions of the denatured polypeptide, or of folding intermediates, with the matrix cause a drastic decrease in renaturation under suboptimal folding conditions. At low salt concentrations, ionic interactions of the refolding polypeptide with the matrix result in lower yields of renaturation. At higher salt concentrations, renaturation is prevented by hydrophobic interactions with the matrix. Apart from ionic strength, renaturation of the denatured matrix-bound fusion protein must be optimized with respect to pH, temperature, cosolvents, and matrix material used. Under optimum conditions, immobilized alpha-glucosidase can be renatured with a high yield at protein concentrations up to 5 mg/ml, whereas folding of the wild-type enzyme in solution is feasible only at an extremely low protein concentration (15 micrograms/ml). Thus, folding of the immobilized alpha-glucosidase allows an extremely high yield of the renaturated model protein. The technology should be applicable to other proteins that tend to aggregate during refolding.

Expression and folding of recombinant bovine prethrombin-2 and its activation to thrombin

Bovine prethrombin-2 has been produced in Escherichia coli using a T7 expression system. The expressed prethrombin-2 formed intracellular inclusion bodies which were solubilized by reversible sulfonation of the cysteines in the presence of 7 M guanidine hydrochloride. Sulfonated prethrombin-2 was refolded in the presence of 4 M guanidine hydrochloride, using oxidized and reduced glutathione as the redox couple. The folded protein was purified by heparin affinity chromatography and activated to thrombin with Echis carinatus snake venom. The resulting thrombin was also purified by heparin affinity chromatography. Kinetic constants were determined for the hydrolysis of H-D-phenylalanyl-L-pipecolyl-L-arginine-p-nitroaniline by recombinant thrombin (kcat = 123 +/- 10 s-1 and Km = 2.91 +/- 0.3 microM). These values are in good agreement with those determined for wild-type thrombin (kcat = 97 +/- 8 s-1 and Km = 2.71 +- 0.25 microM). From the thrombin-mediated release of fibrinopeptide A from fibrinogen, kcat/Km was found to be the same for recombinant (17.3 +/- 1.2 microM-1 s-1) and wild-type (16.7 +/- 2.0 microM-1 s-1) thrombin. These results, taken together with circular dichroism spectra and the elution position of prethrombin-2 from a heparin affinity resin, indicate that prethrombin-2 was folded into a conformation similar to that of the wild-type protein. In addition, since E. coli produces deglycosylated enzymes, these findings suggest that the carbohydrate on the B chain of wild-type thrombin does not affect the amidolytic and fibrinolytic activities of thrombin. Finally, this expression system can be used to prepare mutants of prethrombin-2 for future structure-function studies involving thrombin and its substrates; some preliminary results of this type are presented here.

Renaturation of recombinant proteins produced as inclusion bodies

Expression of recombinant proteins in Escherichia coli often results in the formation of insoluble inclusion bodies. Within the last few years specific methods and strategies have been developed to prepare active proteins from these inclusion bodies. These methods include (i) isolation of inclusion bodies after disintegration of cells by mechanical forces and purification by washing with detergent solutions or low concentrations of denaturant, (ii) solubilization of inclusion bodies with high concentrations of urea or guanidine-hydrochloride in combination with reducing reagents, and (iii) renaturation of the proteins including formation of native disulphide bonds. Renatured and native disulphide bond formation are accomplished by (a) either air oxidation, (b) glutathione reoxidation starting from reduced material, or (c) disulphide interchange starting from mixed disulphides containing peptides. The final yield of renatured proteins can be increased by adding low concentrations of denaturant during renaturation.

Chaperonin-facilitated refolding of ribulosebisphosphate carboxylase and ATP hydrolysis by chaperonin 60 (groEL) are K+ dependent

Both the chaperonin- and MgATP-dependent reconstitution of unfolded ribulosebisphosphate carboxylase (Rubisco) and the uncoupled ATPase activity of chaperonin 60 (groEL) require ionic potassium. The spontaneous, chaperonin-independent reconstitution of Rubisco, observed at 15 but not at 25 degrees C, requires no K+ and is actually inhibited by chaperonin 60, with which the unfolded or partly folded Rubisco forms a stable binary complex. The chaperonin-dependent reconstitution of Rubisco involves the formation of a complex between chaperonin 60 and chaperonin 10 (groES). Formation of this complex almost completely inhibits the uncoupled ATPase activity of chaperonin 60. Furthermore, although the formation of the chaperonin 60-chaperonin 10 complex requires the presence of MgATP, hydrolysis of ATP may not be required, since complex formation occurs in the absence of K+. The interaction of chaperonin 60 with unfolded or partly folded Rubisco does not require MgATP, K+, or chaperonin 10. However, discharge of the complex of chaperonin 60-Rubisco, which leads to the formation of active Rubisco dimers, requires chaperonin 10 and a coupled, K(+)-dependent hydrolysis of ATP. We propose that a role of chaperonin 10 is to couple the K(+)-dependent hydrolysis of ATP to the release of the folded monomers of the target protein from chaperonin 60.

Calcium regulates folding and disulfide-bond formation in alpha-lactalbumin

Refolding and disulfide bond formation in reduced denatured bovine alpha-lactalbumin is shown to be Ca2+-dependent. Whereas in the absence of Ca2+ only about 2% of the native active protein is regenerated, in the presence of Ca2+, almost quantitative renaturation is obtained. A close coupling between Ca2+-binding and native disulfide bond formation is also indicated by spontaneous disulfide scrambling in the apoprotein in the presence of low concentrations of thiols. This phenomenon is not found in other disulfide-containing proteins including the homologous chicken lysozyme. It is proposed that the alpha-lactalbumin Ca2+-binding site has the in vivo function of imposing Ca2+ regulation on the folding of nascent alpha-lactalbumin and thereby on lactose synthesis.

Refolding of serine proteinases

Bovine trypsinogen and chymotrypsinogen were successfully refolded as the mixed disulfide of glutathione using cysteine as the disulfide interchange catalyst. The native structures were regenerated with yields of 40%-50% at pH 8.6 and 4 degrees C, and the half-time for the refolding was approximately 60-75 min. We then refolded threonine-neochymotrypsinogen, which is a two-chain structure held together by disulfide bonds and produced on cleavage of Tyr 146-Thr 147 in native chymotrypsinogen [Duda CT, Light A, J Biol Chem 257 9866-9871, 1982]. Neochymotrypsinogen was denatured and fully reduced, and the thiols were converted to the mixed disulfide of glutathione. The two polypeptide fragments, representing the amino- and carboxyl-terminal domains, were separated on Sephadex G-75. Mixtures of the polypeptide fragments varying in the ratio of their concentration from 1:5 to 5:1 were refolded with yields of 21-28%. The lack of dependence on the concentration of either fragment and the relatively high yields suggest independent folding of the amino- and carboxyl-terminal domains. When the globular structures of the domains formed, they then interacted with one another and produced the native intermolecular disulfide bridge and the proper geometry of the active site.

The influence of effectors on the refolding (reactivation) of immobilized trypsin

The refolding of immobilized trypsin in the presence of various effectors of its enzymatic activity has been studied. Trypsin covalently bound to Sephadex G-200 was made to unfold in a concentrated solution of urea; at the same time its S-S bonds were split with the help of dithiothreitol. The preparation was then separated from the splitting agents, and one of the effectors of the enzymatic activity of trypsin (boric acid, benzamidine, pancreatic or soybean inhibitors of trypsin, N-benzoyl-L-arginine ethyl ester, and N-tosyl-L-arginine methyl ester) was added and the reactivation of immobilized enzyme was studied in the absence of catalysts of thiol-disulphide exchange. The following effects were found. 1. The reactivation of immobilized trypsin in the presence of specific substrates or protein inhibitors proceeds with the same yield (2-5%) as in their absence. 2. In the presence of benzamidine or boric acid (competitive inhibitors) the reactivation yields of the immobilized trypsin increased 5-fold and 12-fold respectively, and became equal to 15% and 40%. Comparison of these results with the statistical probability of formation of the six native S-S bonds from twelve SH groups (approximately 0.01%) shows that if trypsin is made to refold in an immobilized state in the presence of a 'good' effector, the yield of the reactivation of the enzyme can be increased several thousand times. 3. Similar effects were observed for trypsin immobilized on Sepharose 4B. A model is suggested in terms of which the influence of various effectors on trypsin refolding is explained as being a result of their ability to bind with an intermediate folded forms of protein followed by a shift of the equilibrium towards 'regular' conformers.

Reactivation of enzymes irreversibly denatured at elevated temperature. Trypsin and alpha-chymotrypsin covalently immobilized on Sepharose 4B and in polyacrylamide gel

Trypsin (EC 3.4.21.4) and chymotrypsin (EC 3.4.21.2) covalently immobilized on Sepharose or in polyacrylamide gel has been irreversibly denatured at 70--90 degrees C and then reactivated in an almost 100% yield. Thermoinactivated enzyme is first made to unfold under the action of urea with S-S bonds being simultaneously reduced and then made to refold (under the optimal conditions for the thiol-disulfide exchange) into its native conformation. It is demonstrated that the 'irreversible monomolecular thermoinactivation-reactivation' cycle can be repeated many times. The contribution of various mechanisms to thermoinactivation of the enzymes is discussed. Based on the data obtained, the irreversible thermoinactivation of enzymes under investigation should be ascribed only to changes in their secondary and teritary structures; the primary structure is not likely to be affected.

The effect of calcium ion on the urea denaturation of immobilized bovine trypsin

The effect of calcium ion on the urea denaturation of trypsin has been investigated. By using trypsin immobilized on glass beads, all possibilities of autolysis occurring during the denaturation process are eliminated. It was found that in 8 M urea calcium ion markedly decreases the denaturation rate of the immobilized trypsin. Conversely, the presence of calcium ion markedly accelerates the rate of renaturation of denatured immobilized trypsin. Calcium may exert its stabilizing effect on the tertiary structure of the protein by coordination to the side chains of Asp 194, Ser 190 and the carbonyl group of Ser 139 (using the chymotryptic numbering system).

Protein thiol-disulfide interchange and interfacing with biological systems

Disulfide-containing proteins offer unique advantages for mechanistic studies of the formation of native three-dimensional structure from unordered, reduced precursors. The main advantage is that covalent intermediates are formed; by characterizing these intermediates, one obtains substantial information about the reaction pathway. Thiol-disulfide interchange is a major component of most oxidative mechanisms carrying thiol to disulfide; thus, it required some attention in its own right. Afinsen's descriptions of a "shuffle-ase" enzyme led us to examine the rates of the uncatalyzed exchange under physiologically plausible conditions. Somewhat surprisingly, we found that the rates for formation of several native proteins in uncatalyzed systems containing GSSG and GSH are as great as with the "shuffle-ase" enzyme, suggesting that a substantial portion of biological thiol oxidations proceed by uncatalyzed exchange. While thiol-disulfide exchange of course results in no net change in the oxidation level of a system, catalytic linkage of thiol or disulfide to other redox systems provides a mechanism for achieving net changes.