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J Buchner

Publications and source records attributed to J Buchner.

15 recordsLinked to original sources
PubMed1992

GroE dependence of refolding and holoenzyme formation of 6-hydroxy-D-nicotine oxidase.

In Escherichia coli cells expressing 6-hydroxy-D-nicotine oxidase (6-HDNO), a flavoprotein with covalently bound FAD, approximately 40% of the polypeptide is in its apoform. We investigated whether in vivo holoenzyme formation was influenced by the association of the apoenzyme with cellular chaperones. Immunoprecipitation of apoenzyme-containing cell extract with protein-A-Sepharose-bound 6-HDNO- or GroEL-specific antibodies failed to reveal the formation of complexes between these proteins. The limiting factor in holoenzyme formation in vivo appeared to be the intracellular supply of phosphorylated tricarbon compounds (e.g. glycerol-3-P) acting as allosteric effectors in the flavinylation reaction. When holoenzyme formation from purified apo6-HDNO was investigated in vitro, addition of GroEL and GroES to the reaction assays increased the yield of holoenzyme formation. The observed increase in apoenzyme to holoenzyme transition was ATP independent, and the effect of GroE could be simulated by high concentrations of glycerol (40%). Apparently, a nonspecific protein-protein interaction between the GroE proteins and the apo6-HDNO favored holoenzyme formation. The refolding of guanidinium hydrochloride-unfolded holoenzyme, however, was catalyzed by GroEL and GroES in an ATP-dependent reaction. Recovery of the native, enzymatically active, conformation ranged from 30 to 40%. When apo6-HDNO was denatured and refolded, the same dependence on GroE and ATP was observed in the recovery of a conformation able to incorporate FAD and to holoenzyme. [14C] FAD in the refolding assay yielded radioactively labeled 6-HDNO demonstrating the autocatalytical covalent incorporation of FAD into the polypeptide during the folding process.

Apoenzymes↗
PubMed1992

Interaction of GroE with an all-beta-protein.

Molecular chaperones are involved in protein folding both in vivo and in vitro. The Escherichia coli chaperone GroEL interacts with a number of nonnative proteins. A common structural motif of nonnative proteins, which is recognized by GroEL, has not yet been identified. In order to study the role of beta-sheet secondary structure on the interaction of nonnative proteins with GroEL, we used the F(ab) fragment of a monoclonal antibody as a model substrate protein. Here we show that GroEL interacts functionally with this all-beta-protein during reactivation. Antibody fragments refold spontaneously in good yield from the guanidine-denatured state. Functional refolding to the native state is inhibited transiently by GroEL, but there is no complete folding arrest in the absence of Mg-ATP and GroES. The yield of these unspecifically released GroEL-bound F(ab) fragments corresponds to that of the spontaneous reactivation in the absence of chaperones. However, the refolding kinetics in the presence of GroEL are considerably slower. The addition of Mg-ATP to the GroEL.F(ab) complex results in an immediate release of bound substrate protein and a significant increase in the amount of reconstituted antibody fragments compared to spontaneous reactivation. GroES is not essential for functional GroEL-mediated refolding of the F(ab) fragment but affects the reactivation yield to a small extent. Interestingly, stimulation of the GroEL-mediated F(ab) refolding depends primarily on the binding and not on hydrolysis of adenosine triphosphates. Previous results indicate the binding of alpha-helices to GroEL. The results presented in this paper suggest that beta-sheet secondary structural elements are recognized by GroEL. We therefore conclude that the interaction of a nonnative protein with GroEL depends mainly on the nature of the early folding intermediate but not on a specific element of secondary structure.

Adenosine Triphosphate↗
PubMed1992

Hsp90 chaperones protein folding in vitro.

The heat-shock protein Hsp90 is the most abundant constitutively expressed stress protein in the cytosol of eukaryotic cells, where it participates in the maturation of other proteins, modulation of protein activity in the case of hormone-free steroid receptors, and intracellular transport of some newly synthesized kinases. A feature of all these processes could be their dependence on the formation of protein structure. If Hsp90 is a molecular chaperone involved in maintaining a certain subset of cellular proteins in an inactive form, it should also be able to recognize and bind non-native proteins, thereby influencing their folding to the native state. Here we investigate whether Hsp90 can influence protein folding in vitro and show that Hsp90 suppresses the formation of protein aggregates by binding to the target proteins at a stoichiometry of one Hsp90 dimer to one or two substrate molecule(s). Furthermore, the yield of correctly folded and functional protein is increased significantly. The action of Hsp90 does not depend on the presence of nucleoside triphosphates, so it may be that Hsp90 uses a novel molecular mechanism to assist protein folding in vivo.

Animals↗
PubMed1992

Glycosylation inhibits the interaction of invertase with the chaperone GroEL.

During refolding and reassociation of chemically denatured non-glycosylated invertase from Saccharomyces cerevisiae, aggregation competes with correct folding, leading to low yields of reactivation (Kern et al. (1992) Protein Sci. 1, 120-131). In the presence of the chaperone GroEL, refolding is completely arrested. This suggests the formation of a stable complex between GroEL and non-native non-glycosylated invertase. Addition of MgATP results in a slow release of active invertase from the chaperone complex. When GroEL/ES and MgATP are present during refolding, the final reactivation yield increases from 14% to 36%. In contrast, refolding of the core-glycosylated and the high-mannose glycosylated forms of invertase is not arrested by GroEL. Only a short lag phase at the beginning of reactivation and a slightly increased reactivation yield (64% to 86% for core-glycosylated and 62% to 76% for external invertase) indicate a weak interaction of the glycosylated forms with the chaperone.

Bacterial Proteins↗
PubMed1992

Independent domain folding of Pseudomonas exotoxin and single-chain immunotoxins: influence of interdomain connections.

We have studied the refolding of completely unfolded and reduced Pseudomonas exotoxin (PE) and of recombinant single-chain immunotoxins made with monoclonal antibody B3 that are composed of a heavy-chain variable region connected by a flexible linker to the corresponding light-chain variable region (Fv), which is in turn fused to a truncated form of PE. We have found by direct activity assays that different functional domains of these multifunctional proteins fold independently with different kinetics. The ADP-ribosylation domain of PE and of the recombinant immunotoxin fold rapidly, whereas the assembly of the binding and/or translocation domains is regained more slowly. The complete refolding of native PE occurs more rapidly than the refolding of the recombinant immunotoxins. To determine the influence of the connector region between the B3(Fv) moiety and the toxin on the folding process of the recombinant immunotoxin B3(Fv)-PE38KDEL, we have made two different mutations in the peptide that connects the single-chain Fv domain to domain II of PE. These molecules show different folding kinetics, differences in their propensity to aggregate, and different yields of correctly folded molecules. A mutation that decreases aggregation increases the rate of formation and the yield of active immunotoxin molecules.

ADP Ribose Transferases↗
PubMed1992

A method for increasing the yield of properly folded recombinant fusion proteins: single-chain immunotoxins from renaturation of bacterial inclusion bodies.

Many proteins produced in Escherichia coli accumulate in inclusion bodies. We have systematically evaluated the parameters that affect the refolding and renaturation of enzymatically active molecules from bacterial inclusion bodies containing a recombinant single-chain immunotoxin, B3(Fv)-PE38KDEL. This recombinant molecule is composed of the variable domains of monoclonal antibody B3 (B3(Fv)) fused to a truncated mutant form of Pseudomonas exotoxin A (PE38KDEL). This immunotoxin kills carcinoma cells in vitro, causes tumor regression in animal tumor models, and is being developed as an anti-cancer therapeutic agent (Brinkmann et al., 1991, Proc. Natl. Acad. Sci. USA 88, 8616-8620). Like many other recombinant proteins, B3(Fv)-PE38KDEL is produced in E. coli in inclusion bodies and must be denatured and refolded to become active. This requires correct folding, formation of native disulfide bonds, and the association of different domains. All these steps are strongly dependent on the renaturation conditions used. Optimum conditions of refolding were obtained by the addition of reduced and oxidized thiol reagents to promote disulfide bond formation and the addition of a labilizing agent such as L-arginine. Furthermore, the necessity to reactivate proteins at low protein concentrations due to its tendency to aggregate at high concentrations was overcome by a step-by-step addition of denatured and reduced protein into the refolding solution. This approach should be useful for the production of active forms of other recombinant proteins.

ADP Ribose Transferases↗
PubMed1992

Renaturation of a single-chain immunotoxin facilitated by chaperones and protein disulfide isomerase.

B3(Fv)-PE38KDEL, a recombinant immunotoxin, forms inclusion bodies when produced in Escherichia coli. In renaturation experiments, nonspecific aggregation of non-native polypeptide chains, and the formation of incorrect disulfide linkages lead to inactive molecules. To prevent these side reactions, we added molecular chaperones and protein disulfide isomerase (PDI) to the refolding buffer. Both DnaK and GroEL/S influenced the reactivation process. GroEL alone inhibited reactivation, but in the presence of ATP, GroEL and GroES significantly increased the yield of active protein. DnaK also increased the yield of properly folded protein and the stimulating effect of DnaK was also observed using immobilized DnaK, which can be used repeatedly without significant loss of activity. PDI, which catalyzes disulfide bridging of proteins, also stimulated reactivation of the immunotoxin. Under optimum conditions, reactivation yields in the presence of PDI were about twice that obtained with nonenzymatic disulfide bond formation. Furthermore, DnaK and PDI were additive when renaturation was performed in the presence of both proteins.

Antibodies, Monoclonal↗
PubMed1991

Reconstitution of a heat shock effect in vitro: influence of GroE on the thermal aggregation of alpha-glucosidase from yeast.

alpha-Glucosidase from yeast is inactivated rapidly at temperatures above 42 degrees C. The thermal inactivation is accompanied by aggregation. The molecular chaperone GroEL suppresses the formation of aggregates by binding the thermally inactivated alpha-glucosidase. Spectroscopic studies suggest that GroEL binds alpha-glucosidase in an intermediately folded state. The complex between alpha-glucosidase and GroEL can be dissolved by MgATP. GroES accelerates the MgATP-dependent dissociation of the alpha-glucosidase-GroEL complex. At elevated temperatures this release leads to the formation of aggregates, while at lower temperatures native, enzymatically active molecules are formed.

Adenosine Triphosphate↗
PubMed1991

Alternatively folded states of an immunoglobulin.

Well-defined, non-native protein structures of low stability have been increasingly observed as intermediates in protein folding or as equilibrium structures populated under specific solvent conditions. These intermediate structures, frequently referred to as molten globule states, are characterized by the presence of secondary structure, a lack of significant tertiary contacts, increased hydrophobicity and partial specific volume as compared to native structures, and low cooperativity in thermal unfolding. The present study demonstrates that under acidic conditions (pH less than 3) the antibody MAK33 can assume a folded stable conformation. This A-state is characterized by a high degree of secondary structure, increased hydrophobicity, a native-like maximum wavelength of fluorescence emission, and a tendency toward slow aggregation. A prominent feature of this low-pH conformation is the stability against denaturant and thermal unfolding that is manifested in highly cooperative reversible phase transitions indicative of the existence of well-defined tertiary contacts. These thermodynamic results are corroborated by the kinetics of folding from the completely unfolded chain to the alternatively folded state at pH 2. The given data suggest that MAK33 at pH 2 adopts a cooperative structure that differs from the native immunoglobulin fold at pH 7. This alternatively folded state exhibits certain characteristics of the molten globule but differs distinctly from it by its extraordinary structural stability that is characteristic for native protein structures.

Amino Acids↗
PubMed1991

GroE facilitates refolding of citrate synthase by suppressing aggregation.

The molecular chaperone GroE facilitates correct protein folding in vivo and in vitro. The mode of action of GroE was investigated by using refolding of citrate synthase as a model system. In vitro denaturation of this dimeric protein is almost irreversible, since the refolding polypeptide chains aggregate rapidly, as shown directly by a strong, concentration-dependent increase in light scattering. The yields of reactivated citrate synthase were strongly increased upon addition of GroE and MgATP. GroE inhibits aggregation reactions that compete with correct protein folding, as indicated by specific suppression of light scattering. GroEL rapidly forms a complex with unfolded or partially folded citrate synthase molecules. In this complex the refolding protein is protected from aggregation. Addition of GroES and ATP hydrolysis is required to release the polypeptide chain bound to GroEL and to allow further folding to its final, active state.

Animals↗
PubMed1991

Routes to active proteins from transformed microorganisms.

Over-expression of recombinant proteins in microbial hosts results in the formation of active soluble protein or of insoluble aggregates (inclusion bodies). Efficient in vitro refolding strategies have been developed to reactivate inactive proteins from inclusion bodies. Co-expression of molecular chaperones may provide a tool to promote correct structure formation of recombinant proteins in vivo.

Cloning, Molecular↗
PubMed1991

Renaturation, purification and characterization of recombinant Fab-fragments produced in Escherichia coli.

Cytoplasmatic expression of murine antibody chains in Escherichia coli results in the formation of insoluble and inactive protein aggregates (inclusion bodies). By systematic variation of the parameters influencing the folding, formation of disulfide bonds and association of the constituent polypeptide chains, we have designed a renaturation procedure allowing the production of microbially expressed Fab-fragments at yields up to 40 percent of the total amount of recombinant protein. The strategy of optimization is generally applicable for disulfide containing proteins produced as inclusion bodies in bacteria. The purified recombinant antibody fragments obtained are identical with the native murine Fab in all functional and physicochemical parameters tested.

Animals↗
PubMed1991

Protein aggregation in vitro and in vivo: a quantitative model of the kinetic competition between folding and aggregation.

Protein aggregation is frequently observed as a major side-reaction of protein folding. We present quantitative models explaining the formation of aggregates during protein folding in vitro and in vivo on the basis of a kinetic competition between correct folding and aggregation reactions. Both models are in good agreement with experimental data. The model implies that, in vitro, the yield of native protein obtained upon refolding is determined by the rates of the competing first order folding and second order aggregation reactions. Therefore, a high protein concentrations aggregation dominates over folding and leads to the formation of insoluble protein. For in vivo protein synthesis, the model shows that the yield of native protein is only dependent on the rate of folding, on the rate of aggregation and on the rate of protein synthesis. In the cell, several mechanisms, including "folding helpers" seem to have evolved, which influence these processes and thereby prevent unproductive side reactions.

Kinetics↗