GroEL-assisted dehydrogenase folding mediated by coenzyme is ATP-independent.

It has been commonly accepted that GroEL functions as a chaperone by modulation of its affinity for folding intermediates through binding and hydrolysis of ATP. However, we have found that NAD, as a coenzyme of d-glyceraldehyde-3-phosphate dehydrogenase (GAPDH), also stimulates the discharge of GAPDH folding intermediate from its stable complex with GroEL formed in the absence of ATP and assists refolding with the same yield as ATP/Mg(2+) does. The reactivation further increases when ATP is also present, but addition of Mg(2+) has no more effect. NADP, a coenzyme of glucose-6-phosphate dehydrogenase, also releases its folding intermediates from GroEL and increases reactivation. Different from ATP, NAD triggers the release of GAPDH intermediates bound by GroEL via binding with GAPDH itself but not with GroEL, and the released intermediates all folded to native molecules without the formation of aggregation. The collaborative effects of coenzyme and GroEL mediate GroEL-assisted dehydrogenase folding in an ATP-independent way.     

Effects of macromolecular crowding on the unfolding and the refolding of D-glyceraldehyde-3-phosophospate dehydrogenase

The effects of crowding agents, polyethylene glycol (PEG 20K), Dextran 70, and bovine serum albumin, on the denaturation of homotetrameric D-glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) in 0.5 M guanidine hydrochloride and the reactivation of the fully denatured enzyme have been examined quantitatively. Increasing the concentration of PEG 20K to 225 mg/ml decreases the rate constant of slow phase of GAPDH inactivation to 5% but with no change for the fast phase. Chaperone GroEL assists GAPDH refolding greatly and shows even higher efficiency under crowding condition. Crowding mainly affects refolding steps after the formation of the dimeric folding intermediate.     

Inhibition of chaperonin GroEL by a monomer of ovine prion protein and its oligomeric forms

The possibility of inhibition of chaperonin functional activity by amyloid proteins was studied. It was found that the ovine prion protein PrP as well as its oligomeric and fibrillar forms are capable of binding with the chaperonin GroEL. Besides, GroEL was shown to promote amyloid aggregation of the monomeric and oligomeric PrP as well as PrP fibrils. The monomeric PrP was shown to inhibit the GroEL-assisted reactivation of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The oligomers of PrP decelerate the GroEL-assisted reactivation of GAPDH, and PrP fibrils did not affect this process. The chaperonin GroEL is capable of interacting with GAPDH and different PrP forms simultaneously. A possible role of the inhibition of chaperonins by amyloid proteins in the misfolding of the enzymes involved in cell metabolism and in progression of neurodegenerative diseases of amyloid nature is discussed.     

Non-native glyceraldehyde-3-phosphate dehydrogenase can be an intrinsic component of amyloid structures

Interactions between different forms of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and amyloid-beta peptide (1-42) were investigated by direct (surface plasmon resonance) and indirect (kinetics of spontaneous and GroEL/S-assisted reactivation of denatured GAPDH) methods. It was demonstrated that non-native forms of GAPDH obtained by different ways (cold denaturation, oxidation of the enzyme, and its unfolding in guanidine hydrochloride) efficiently bind to soluble amyloid-beta peptide (1-42) yielding a stable complex. Native tetrameric GAPDH does not interact with soluble amyloid-beta peptide (1-42), neither non-native forms of GAPDH interact with aggregated amyloid-beta peptide (1-42). The results suggest that non-native GAPDH species can be involved in the formation of amyloid structures during Alzheimer's disease, binding to soluble amyloid-beta peptide (1-42).     

Misfolded forms of glyceraldehyde-3-phosphate dehydrogenase interact with GroEL and inhibit chaperonin-assisted folding of the wild-type enzyme

We studied the interaction of chaperonin GroEL with different misfolded forms of tetrameric phosphorylating glyceraldehyde-3-phosphate dehydrogenase (GAPDH): (1) GAPDH from rabbit muscles with all SH-groups modified by 5,5'-dithiobis(2-nitrobenzoate); (2) O-R-type dimers of mutant GAPDH from Bacillus stearothermophilus with amino acid substitutions Y283V, D282G, and Y283V/W84F, and (3) O-P-type dimers of mutant GAPDH from B. stearothermophilus with amino acid substitutions Y46G/S48G and Y46G/R52G. It was shown that chemically modified GAPDH and the O-R-type mutant dimers bound to GroEL with 1:1 stoichiometry and dissociation constants K(d) of 0.4 and 0.9 muM, respectively. A striking feature of the resulting complexes with GroEL was their stability in the presence of Mg-ATP. Chemically modified GAPDH and the O-R-type mutant dimers inhibited GroEL-assisted refolding of urea-denatured wild-type GAPDH from B. stearothermophilus but did not affect its spontaneous reactivation. In contrast to the O-R-dimers, the O-P-type mutant dimers neither bound nor affected GroEL-assisted refolding of the wild-type GAPDH. Thus, we suggest that interaction of GroEL with certain types of misfolded proteins can result in the formation of stable complexes and the impairment of chaperonin activity.     

Stability and release requirements of the complexes of GroEL with two homologous mammalian aminotransferases

The mitochondrial (mAAT) and cytosolic (cAAT) homologous isozymes of aspartate aminotransferase are two relatively large proteins that in their nonnative states interact very differently with GroEL. MgATP alone can increase the rate of GroEL-assisted reactivation of cAAT, yet the presence of GroES is mandatory for mAAT. Addition of an excess of a denatured substrate accelerates reactivation of cAAT in the presence of GroEL, but has no effect on mAAT. These competition studies suggest that the more stringent substrate mAAT forms a thermodynamically stable complex with GroEL, while rebinding affects the slow reactivation kinetics of cAAT with GroEL alone. However, the competitor appears to accelerate the release of cAAT from GroEL, most likely by displacing bound cAAT from the GroEL cavity. Moreover, cAAT, but not mAAT, shows a time-dependent increase in protease resistance while bound to GroEL at low temperature. These results suggest that folding and release of cAAT from GroEL in the absence of cofactors may occur stepwise with certain interactions being broken and reformed until the protein escapes binding. The distinct behavior of these two isozymes most likely results from differences in the structure of the nonnative states that bind to GroEL.     

Renaturation of citrate synthase: influence of denaturant and folding assistants.

Citrate synthase (CS), which has been denatured in either guanidine hydrochloride (GdnHCl) or urea can be assisted in its renaturation in a variety of ways. The addition of each of the assistants--bovine serum albumin (BSA), oxaloacetate (OAA), and glycerol--promotes renaturation. In combination, the effect of these substances is additive with respect to the yield of folded CS. The report of Buchner et al. (Buchner, J., Schmidt, M., Fuchs, M., Jaenicke, R., Rudolph, R., Schmid, F.X., & Kiefhaber, T., 1991, Biochemistry 30, 1586-1591) that refolding of CS is facilitated by the GroE system (an Escherichia coli chaperonin [cpn] that is composed of GroEL [cpn60] and GroES [cpn10]) has been confirmed. However, we observed substantially higher yield of reactivated CS, 82%, and almost no reactivation in the absence of GroES, < 5%, whereas Buchner et al. reported 28% and 16%, respectively. In addition, we find that GroE-assisted refolding is more efficient for CS denatured in GdnHCl than for CS denatured in urea. This result is discussed in light of the known difference in the denatured states generated in GdnHCl and urea. Because GroEL inhibits the BSA/glycerol/OAA-assisted refolding, this system will be useful in future studies on the mechanism of GroE-facilitated refolding.     

A stable cold folding intermediate of rabbit muscle D-glyceraldehyde 3-phosphate dehydrogenase.

With decreasing temperature the reactivation yield of denatured D-glyceraldehyde 3-phosphate dehydrogenase (GAPDH) upon dilution increases but the reactivation rate decreases. Neither reactivation nor aggregation during refolding can be detected at 4 degrees C in 48 h, and at 3 degrees C even in 6 days. However, the reactivation takes place once the temperature is raised with little decrease of the yield after incubation for 6 days at 3 degrees C. A cold folding intermediate forms in a burst phase of refolding at 4 degrees C as shown by a fast change of the intrinsic fluorescence followed by further conformational adjustment to a stable state in about 1 h. The stable folding intermediate has been characterized to be a dimer of partially folded GAPDH subunit with secondary structure between that of the native and denatured enzymes, a hydrophobic cluster not found in either the native or the denatured state, and an active site similar to but different from that of the native state. Chaperonin 60 (GroEL) binds with all intermediates formed at 4 degrees C, but the intermediates formed at the early folding stage reactivate with higher yield than those formed after conformational adjustment when dissociated from GroEL in the presence of ATP and further folded and assembled into the native tetramer.     

Participation of chaperonin GroEL in the folding of D-glyceraldehyde-3-phosphate dehydrogenase. An approach based on the use of different oligomeric forms of the enzyme immobilized on sepharose

The binding of denatured B. stearothermophilus D-glyceraldehyde-3-phosphate dehydrogenase (GAPDH) to the E. coli chaperonin GroEL was investigated in two systems: (1) GroEL immobilized on Sepharose via a single subunit was titrated with urea-denatured soluble GAPDH and (2) a Sepharose-bound denatured GAPDH monomer was titrated with soluble GroEL. Similar apparent K _D values for the complex GroEL·GAPDH were obtained in both cases (0.04 and 0.03 M, respectively), the stoichiometry being 1.0 mol chaperonin per GAPDH subunit in the system with the immobilized GroEL and 0.2 mol chaperonin per Sepharose-bound GAPDH monomer. Addition of GroEL and Mg·ATP to a reactivation mixture increased the yield of reactivation of both E. coli and B. stearothermophilus GAPDHs. Incubation of the Sepharose-bound catalytically active tetrameric and dimeric GAPDH forms with the protein fraction of a wild-type E. coli cell extract resulted in the binding of GroEL to the dimer and no interaction with the tetrameric form. These data suggest that GroEL may be capable of interacting with the interdimeric contact regions of the folded GAPDH dimers.     

GroEL and protein disulfide isomerase each binds with folding intermediates of D-glyceraldehyde-3-phosphate dehydrogenase released from complexes formed with the other

Simultaneous presence of two chaperones, GroEL and protein disulfide isomerase (PDI), assists the reactivation of denatured D-glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in an additive way. Delayed addition of chaperones to the refolding solution after dilution of denatured GAPDH indicates an interaction with intermediates formed mainly in the first 5 min for PDI and formed within a longer time period for GroEL-ATP. The above indicate that the two chaperones interact with different folding intermediates of GAPDH. After delayed addition of one chaperone to the refolding mixture containing the other at 4°C, GroEL binds with all GAPDH intermediates dissociated from PDI, and PDI interacts with the intermediates released from GroEL during the first 10–20 min. It is suggested that the GAPDH folding intermediates released from the chaperone-bound complex are still partially folded so as to be rebound by the other chaperone. The above results clearly support the network model of GroEL and PDI.     

Non-functioning chaperonin GroEL stimulates protein aggregation

To clarify the role of chaperones in the development of amyloid diseases, the interaction of the chaperonin GroEL with misfolded proteins and recombinant prions has been studied. The efficiency of the chaperonin-assisted folding of denatured glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was shown to be decreased in the presence of prions. Prions are capable of binding to GroEL immobilized on Sepharose, but this does not prevent the interaction between GroEL and other denatured proteins. The size of individual proteins (GroEL, GAPDH, and the recombinant prion) and aggregates formed after their mixing have been determined by the dynamic light scattering analysis. It was shown that at 25°C, the non-functioning chaperonin (equimolar mixture of GroEL and GroES in the absence of Mg-ATP) bound prion yielding large aggregates (greater than 400 nm). The addition of Mg-ATP decreased significantly the size of the aggregates to 70–80 nm. After blocking of one of the chaperonin active sites by oxidized denatured GAPDH, the aggregate size increased to 1200 nm, and the addition of Mg-ATP did not prevent the aggregation. These data indicate the significant role of chaperonins in the formation of amyloid structures and demonstrate the acceleration of aggregation in the presence of functionally inactive chaperonins. The suggested model can be used for the analysis of the efficiency of antiaggregants in the system containing chaperonins.     

Molecular cloning of groESL locus, and purification and characterization of chaperonins, GroEL and GroES, from Bacillus brevis

The groESL locus of a protein-hypersecreting bacterium, Bacillus brevis, was cloned by PCR using primers designed based on the DNA sequence of a B. subtilis homolog. GroEL protein was purified to apparent homogeneity and its ATPase activity was characterized: it hydrolyzed ATP, CTP, and TTP in this order of reaction rate, and its specific activity for ATP was 0.1 micromole/min/mg protein. Purified GroEL forms a tetradecamer. GroEL was estimated to contain 22% alpha-helix, 24% beta-sheet, and 19% turn structures, by CD measurement. GroES protein was also highly purified to examine its chaperonin activity. GroEL protected from thermal inactivation of and showed refolding-promoting activity for malate dehydrogenase, strictly depending on the presence of ATP and GroES.     

Study of refolding of calf intestinal alkaline phosphatase

Calf intestinal alkaline phosphatase (CIP) was denatured in 3.0 M guanidine hydrochloride for 2 h at 25 degrees C, before being diluted 20-fold with 0.1 M, pH 8.0, Tris-HCl buffer solution containing various effector molecules such as Mg2+, Zn2+, and nucleotide phosphate. The reactivation courses of the enzyme were investigated by the level of activity recovery, the recovery rate constant, and the relative standard deviation of the data. In the presence of effectors, the courses under reducing and nonreducing conditions of disulfide bonds of protein were compared. It was concluded that for CIP, Mg2+ is a more efficient inducer of reconstitution of the active site and appears to play a specific role. In addition, the present study discusses the differences in the refolding effectors between bacterial and mammalian enzymes.     

Chaperonin-assisted folding of glutamine synthetase under nonpermissive conditions: off-pathway aggregation propensity does not determine the co-chaperonin requirement

One of the proposed roles of the GroEL-GroES cavity is to provide an "infinite dilution" folding chamber where protein substrate can fold avoiding deleterious off-pathway aggregation. Support for this hypothesis has been strengthened by a number of studies that demonstrated a mandatory GroES requirement under nonpermissive solution conditions, i.e., the conditions where proteins cannot spontaneously fold. We have found that the refolding of glutamine synthetase (GS) does not follow this pattern. In the presence of natural osmolytes trimethylamine N-oxide (TMAO) or potassium glutamate, refolding GS monomers readily aggregate into very large inactive complexes and fail to reactivate even at low protein concentration. Surprisingly, under these "nonpermissive" folding conditions, GS can reactivate with GroEL and ATP alone and does not require the encapsulation by GroES. In contrast, the chaperonin dependent reactivation of GS under another nonpermissive condition of low Mg2+ (<2 mM MgCl2) shows an absolute requirement of GroES. High-performance liquid chromatography gel filtration analysis and irreversible misfolding kinetics show that a major species of the GS folding intermediates, generated under these "low Mg2+" conditions exist as long-lived metastable monomers that can be reactivated after a significantly delayed addition of the GroEL. Our results indicate that the GroES requirement for refolding of GS is not simply dictated by the aggregation propensity of this protein substrate. Our data also suggest that the GroEL-GroES encapsulated environment is not required under all nonpermissive folding conditions.     

Chaperone-Like Manner of Human Neuronal Tau Towards Lactate Dehydrogenase

In our experiments, inactivation of lactate dehydrogenase (LDH, EC1.1.1.27) in the presence of human microtubule-associated tau is observably suppressed during thermal and guanidine hydrochloride (GdnHCl) denaturation. Kinetic studies show tau can prevent LDH from self-aggregation monitored by light scattering during thermal denaturation. On the other hand, neuronal tau promotes reactivation of LDH and suppresses self-aggregation of non-native LDH when GdnHCl solution is diluted. Furthermore, the reactivation yield of LDH decreases significantly with delayed addition of tau. All experiments were completed in the reducing buffer with 1 mM DTT to avoid between tau and LDH forming the covalent bonds during unfolding and refolding. Thus, Tau prevents proteins from misfolding and aggregating into insoluble, nonfunctional inclusions and assists them to refold to reach the stable native state by binding to the exposed hydrophobic patches on proteins instead of by forming or breaking covalent bonds. Additionally, tau remarkably enhances reactivation of GDH (glutamic dehydrogenase, EC 1.4.1.3), another carbohydrate metabolic enzyme, also showing a chaperone-like manner. It suggests that neuronal tau non-specifically functions a chaperone-like protein towards the enzymes of carbohydrate metabolism.     

Comparative Analysis of the Effects of α-Crystallin and GroEL on the Kinetics of Thermal Aggregation of Rabbit Muscle Glyceraldehyde-3-Phosphate Dehydrogenase

Effects of α-crystallin and GroEL on the kinetics of thermal aggregation of rabbit muscle glyceraldehyde-3-phosphate dehydrogenase (GAPDH) have been studied using dynamic light scattering and analytical ultracentrifugation. The analysis of the initial parts of the dependences of the hydrodynamic radius of protein aggregates on time shows that in the presence of α-crystallin or GroEL the kinetic regime of GAPDH aggregation is changed from the regime of diffusion-limited cluster–cluster aggregation to the regime of reaction-limited cluster–cluster aggregation, wherein the sticking probability for the colliding particles becomes lower the unity. In contrast to α-crystallin, GroEL does not interfere with formation of the start aggregates which include denatured GAPDH molecules. On the basis of the analytical ultracentrifugation data the conclusion has been made that the products of dissociation of GAPDH and α-crystallin or GroEL play an important role in the interactions of GAPDH and chaperones at elevated temperatures.     

Effects of ATP on the stability of enzymes against heat treatment in 6-aminonicotinamide treated quail

The stabilities of liver and pectoral muscle enzymes in 6-aminonicotinamide (6-AN) treated quail against heat treatment in the presence and absence of added ATP were investigated. Only ATP level in the brain and pectoral muscle of 6-AN treated group was significantly reduced compared to the control group whereas ADP and AMP levels were not affected. In the thermal stability (55 degrees C) of liver enzymes, the activity of acetylcholinesterase (AChE) was not affected whereas the activities of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and lactate dehydrogenase (LDH) were significantly lowered (P<0.01). The addition of 1mM ATP to liver enzyme extracts of 6-AN group afforded 4- and 1.7-fold more protection for GAPDH and LDH, respectively (P<0.01). In liver, LDH appeared to be more protected by ATP than GAPDH. In muscle, however, GAPDH and AChE activity were significantly affected but not LDH. The addition of 1mM ATP to muscle enzyme extracts of 6-AN group afforded 1.7-fold more protection for GAPDH (P<0.01) but rather inactivated AChE. A marked reduction in ATP levels in muscle did not affect specifically muscle enzyme activities only since liver enzyme activities were also affected to the same degree as muscle.     

"Half of the sites" binding of D-glyceraldehyde-3-phosphate dehydrogenase folding intermediate with GroEL

Two D-glyceraldehyde-3-phosphate dehydrogenase (GAPDH) folding intermediate subunits bind with chaperonin 60 (GroEL) to form a stable complex, which can no longer bind with additional GAPDH intermediate subunits, but does bind with one more lysozyme folding intermediate or one chaperonin 10 (GroES) molecule, suggesting that the two GAPDH subunits bind at one end of the GroEL molecule displaying a "half of the sites" binding profile. For lysozyme, GroEL binds with either one or two folding intermediates to form a stable 1:1 or 1:2 complex with one substrate on each end of the GroEL double ring for the latter. The 1:1 complex of GroEL.GroES binds with one lysozyme or one dimeric GAPDH folding intermediate to form a stable ternary complex. Both complexes of GroEL.lysozyme1 and GroEL.GAPDH2 bind with one GroES molecule only at the other end of the GroEL molecule forming a trans ternary complex. According to the stoichiometry of GroEL binding with the GAPDH folding intermediate and the formation of ternary complexes containing GroEL.GAPDH2, it is suggested that the folding intermediate of GAPDH binds, very likely in the dimeric form, with GroEL at one end only.     

Binding of a chaperonin to the folding intermediates of lactate dehydrogenase.

When Bacillus stearothermophilus LDH dimer is incubated with increasing concentrations of the denaturant guanidinium chloride, three distinct unfolded states of the molecule are observed at equilibrium [Smith, C. J., et al. (1991) Biochemistry 30, 1028-1036]. The kinetics of LDH refolding are consistent with an unbranched progression through these states. The Escherichia coli chaperonin, GroEL, binds with high affinity to the completely denatured form and more weakly to the earliest folding intermediate, thus retarding the refolding process. A later structurally defined folding intermediate, corresponding to a molten globule form, is not bound by GroEL; neither is the inactive monomer. The complex between GroEL and denatured LDH is destabilized by the binding of magnesium/ATP (Mg/ATP) or by the nonhydrolyzable analogue adenylyl imidodiphosphate (AMP-PNP). From our initial kinetic data, we propose that GroEL exists in two interconvertible forms, one of which is stabilized by the binding of Mg/ATP but associates weakly with the unfolded protein. The other is destabilized by Mg/ATP and associates strongly with unfolded LDH. The relevance of these findings to the role of GroEL in vivo is discussed.     

Native-like intermediate on the folding pathway of Escherichia coli succinyl-CoA synthetase

The transition between the native and denatured states of the tetrameric succinyl-CoA synthetase from Escherichia coli has been investigated by circular dichroism, fluorescence spectroscopy, cross-linking by glutaraldehyde and activity measurements. At pH 7.4 and 25 degrees C, both denaturation of succinyl-CoA synthetase by guanidine hydrochloride and refolding of the denatured enzyme have been characterized as reversible reactions. In the presence of its substrate ATP, the denatured enzyme could be successfully reconstituted into the active enzyme with a yield of 71-100%. Kinetically, reacquisition of secondary structure by the denatured enzyme was rapid and occurred within 1 min after refolding was initiated. On the other hand, its reactivation was a slow process which continued up to 25 min before 90% of the native activity could be restored. Both secondary and quaternary structures of the enzyme, reconstituted in the absence of ATP, were indistinguishable from those of the native enzyme but the renatured protein was catalytically inactive. This observation indicates the presence of catalytically inactive tetramer as an intermediate in the reconstitution process. The reconstituted protein could be reactivated by ATP even 10 min after the reacquisition of the native secondary structure by the refolding protein. However, reactivation of the protein by ATP 60 min after the regain of secondary structure was significantly less, suggesting that rapid refolding and reassociation of the monomers into a native-like tetramer and reactivation of the tetramer are sequential events; the latter involving slow and small conformational rearrangements in the refolded enzyme that are likely to be associated with phosphorylation.