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J B Chaudhuri

Publications and source records attributed to J B Chaudhuri.

12 recordsLinked to original sources
PubMed2000

Refolding and purification of a urokinase plasminogen activator fragment by chromatography.

A fragment of recombinant urokinase plasminogen activator (u-PA), was expressed in E. coli in the form of inclusion bodies. Purification and renaturation was achieved in a three-stage process. Capture of the inclusion bodies was achieved by coupling wash steps in Triton X-100 and urea with centrifugation. Solubilised inclusion bodies were then renatured by buffer exchange performed by size-exclusion chromatography (SEPROS). Use of size-exclusion media with higher fractionation ranges resulted in an increase in the recovery of u-PA activity, to a maximum fractionation range of Mr 10000-1500000 after which recovery is reduced, due to a low resolution between the refolded u-PA and denaturant. Fractions of refolded u-PA were concentrated using cation ion-exchange chromatography, which selectively binds correctly folded u-PA. The result is concentrated, active, homogeneous u-PA.

Chromatography, Gel↗
PubMed1999

Considerations of sample application and elution during size-exclusion chromatography-based protein refolding.

A mechanism for size-exclusion chromatography-based protein refolding is described. The model considers the steps of loading the denatured protein onto a gel filtration column, and protein elution. The model predictions are compared with results of refolding lysozyme (10 and 20 mg/ml) using Superdex 75 HR. The main collapse in protein structure occurred immediately after loading, where the partition coefficient of unfolded lysozyme increased from 0.1 to 0.48 for the partially folded molecule. Use of a refolding buffer as the mobile phase resulted in complete refolding of lysozyme; this eluted at an elution volume of 15.6 ml with a final partition coefficient of 0.54. The model predicted the elution volume of refolded lysozyme at 19.3 ml.

Buffers↗
PubMed1999

Expression, reactivation, and purification of enzymes from Haloferax volcanii in Escherichia coli.

Enzymes from extreme halophiles have potential as catalysts in biotransformations. We have developed methods for the expression in Escherichia coli and purification of two enzymes from Haloferax volcanii: dihydrolipoamide dehydrogenase and citrate synthase. Both enzymes were expressed in E. coli using the cytoplasmic expression vectors, pET3a and pET3d. Citrate synthase was soluble and inactive, whereas dihydrolipoamide dehydrogenase was expressed as inclusion bodies. Citrate synthase was reactivated following overnight incubation in 2 M KCl, and dihydrolipoamide dehydrogenase was refolded by solubilisation in 8 M urea followed by dilution into a buffer containing 2 M KCl, 10 microM FAD, 1 mM NAD, and 0.3 mM GSSG/3 mM GSH. Maximal activity was obtained after 3 days incubation at 4 degrees C. Purification of the two active enzymes was carried out using high-resolution methods. Dihydrolipoamide dehydrogenase was purified using copper-based metal ion affinity chromatography in the presence of 2 M KCl. Citrate synthase was recovered using dye-affinity chromatography in the presence of salt. A high yield of active enzyme was obtained in both cases. Following purification, characterisation of both recombinant proteins showed that their kinetics and salt-dependence were comparable to those of the native enzymes. Expression of active protein was attempted both by growth of E. coli in the presence of salt and betaine, and also by using periplasmic expression vectors in combination with a high salt growth media. Neither strategy was successful.

Base Sequence↗
PubMed1999

Inclusion body purification and protein refolding using microfiltration and size exclusion chromatography.

The presence of inclusion body impurities can affect the refolding yield of recombinant proteins, thus there is a need to purify inclusion bodies prior to refolding. We have compared centrifugation and membrane filtration for the washing and recovery of inclusion bodies of recombinant hen egg white lysozyme (rHEWL). It was found that the most significant purification occurred during the removal of cell debris. Moderate improvements in purity were subsequently obtained by washing using EDTA, moderate urea solutions and Triton X-100. Centrifugation between each wash step gave a purer product with a higher rHEWL yield. With microfiltration, use of a 0.45 micron membrane gave higher solvent fluxes, purer inclusion bodies and greater protein yield as compared with a 0.1 micron membrane. Significant flux decline was observed for both membranes. Second, we studied the refolding of rHEWL. Refolding from an initial concentration of 1.5 mg ml-1, by 100-fold batch dilution gave a 43% recovery of specific activity. Purified inclusion bodies gave rise to higher refolding yields, and negligible activity was observed after refolding partially purified material. Refolding rHEWL with a size exclusion chromatography based process gave rise to a refolding yield of 35% that corresponded to a 20-fold dilution.

Animals↗
PubMed1998

Sucrose enhances the recovery and activity of ribonuclease A during reversed micelle extraction.

We have investigated the effect of two simple sugars, glucose and sucrose, on the extraction of ribonuclease A by AOT-isooctane reversed micelles. Including the sugars at concentrations up to 0.75 M in the feed solution resulted in moderate improvements in the forward transfer efficiency. The greatest effects were seen observed in the backward transfer step where both the protein recovery yield and the activity of the protein were greatly increased. Protein transfer and activity yields were also dependent on the AOT concentration. We suggest that the presence of sucrose, which was solubilized into the reversed micelles, results in preferential hydration of ribonuclease A, reducing the protein-surfactant interactions.

Animals↗
PubMed1998

Improved protein refolding using hollow-fibre membrane dialysis.

We have used a cellulose acetate, hollow-fibre (HF) ultrafiltration membrane to refold bovine carbonic anhydrase, loaded into the lumen space, by removing the denaturant through controlled dialysis via the shell side space. When challenged with GdnHCl-denatured carbonic anhydrase, 70% of the loaded protein reptated through the membrane into the circulating dialysis buffer. Reptation occurred because the protein, in its fully unfolded configuration, was able to pass through the pores. The loss of carbonic anhydrase through the membrane was controlled by the dialysis conditions. Dialysis against 0.05 M Tris-HCl for 30 min reduced the denaturant around the protein to a concentration that allowed the return of secondary structure, increasing the hydrodynamic radius, thus preventing protein transmission. Under these conditions a maximum of 42% of carbonic anhydrase was recovered (from a starting concentration of 5 mg/mL) with 94% activity. This is an improvement over refolding carbonic anhydrase by simple batch dilution, which gave a maximum reactivation of 85% with 35% soluble protein yield. The batch refolding of carbonic anhydrase is very sensitive to temperature; however, during HF refolding between 0 and 25 degrees C the temperature sensitivity was considerably reduced. In order to reduce the convection forces that give rise to aggregation and promote refolding the dialyzate was slowly heated from 4 to 25 degrees C. This slow, temperature-controlled refolding gave an improved soluble protein recovery of 55% with a reactivation yield of 90%. The effect of a number of additives on the refolding system performance were tested: the presence of PEG improved both the protein recovery and the recovered activity from the membrane, while the detergents Tween 20 and IGEPAL CA-630 increased only the refolding yield.

Animals↗
PubMed1997

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.

Buffers↗
PubMed1996

Protein folding in vivo and renaturation of recombinant proteins from inclusion bodies.

Eukaryotic proteins expressed in Escherichia coli often accumulate within the cell as insoluble protein aggregates or inclusion bodies. The recovery of structure and activity from inclusion bodies is a complex process, there are no general rules for efficient renaturation. Research into understanding how proteins fold in vivo is giving rise to potentially new refolding methods, for example, using molecular chaperones. In this article we review what is understood about the main three classes of chaperone: the Stress 60, Stress 70, and Stress 90 proteins. We also give an overview of current process strategies for renaturing inclusion bodies, and report the use of novel developments that have enhanced refolding yields.

Humans↗
PubMedDate not supplied

Recovery and reuse of the molecular chaperone GroEL for in vitro protein refolding.

The chaperones GroEL and GroES from Escherichia coli are known to improve in vitro protein refolding yields. We show that, for the molecular chaperone-assisted refolding of hen egg white lysozyme, GroES is not an essential requirement and that activity is recovered with GroEL and ATP alone. The refolding yields of lysozyme in the presence of GroEL are much greater than those obtained by dilution because of a reduction in protein aggregation. On the basis of the large difference in molecular weight between the GroEL complex (MW 840 000) and lysozyme (MW 14 600), we have demonstrated that using an ultrafiltration membrane (MW 30 000) GroEL may be easily retained after refolding while lysozyme passes freely into the permeate. The chaperonin recovered from the refolding solution was then reused several times for further refolding experiments. The effectiveness of GroEL-assisted refolding was found to decrease with reuse, and this has been attributed to a reduction in the GroEL:lysozyme molar ratio.

Chaperonin 60↗
PubMedDate not supplied

Protein purification by ultrafiltration using a beta-galactosidase fusion tag.

The use of beta-galactosidase (465 kDa) as a fusion tag for ultrafiltration-based protein purification has been investigated. The target protein studied was thermophilic glucose dehydrogenase (157 kDa, GDH) from Thermoplasma acidophilum. An expression vector was constructed comprising the lacZ gene fused to a factor Xa cleavage sequence that was attached to the 5' end of the GDH gene. This gene fusion was expressed in Escherichia coli JM109 to yield a soluble protein that exhibited activities for both enzymes. Cleavage of this fusion protein (622 kDa) by factor Xa gave two smaller proteins that showed individual beta-galactosidase and GDH activity. A two-stage diafiltration process for protein purification was used in an ultrafiltration stirred cell. In the first stage, a 500 kDa membrane was used to retain the fusion protein and transmit smaller E. coli host proteins. Approximately 80% of the GDH activity was retained in this step. Following cleavage, the second stage utilized a 300 kDa membrane to fractionate the beta-galactosidase and GDH. No beta-galactosidase was detected in the permeate solutions, and 97% of the GDH activity was recovered in the permeate.

Chemical Fractionation↗