GroES in the asymmetric GroEL14-GroES7 complex exchanges via an associative mechanism.
The interaction of the chaperonin GroEL14 with its cochaperonin GroES7 is dynamic, involving stable, asymmetric 1:1 complexes (GroES7.GroEL7-GroEL7) and transient, metastable symmetric 2:1 complexes [GroES7.GroEL7-GroEL7.GroES7]. The transient formation of a 2:1 complex permits exchange of free GroES7 for GroES7 bound in the stable 1:1 complex. Electrophoresis in the presence of ADP was used to resolve free GroEL14 from the GroES7-GroEL14 complex. Titration of GroEL14 with radiolabeled GroES7 to molar ratios of 32:1 demonstrated a 1:1 limiting stoichiometry in a stable complex. No stable 2:1 complex was detected. Preincubation of the asymmetric GroES7.GroEL7-GroEL7 complex with excess unlabeled GroES7 in the presence of ADP demonstrated GroES7 exchange. The rates of GroES7 exchange were proportional to the concentration of unlabeled free GroES7. This concentration dependence points to an associative mechanism in which exchange of GroES7 occurs by way of a transient 2:1 complex and excludes a dissociative mechanism in which exchange occurs by way of free GroEL14. Exchange of radiolabeled ADP from 1:1 complexes was much slower than the exchange of GroES7. In agreement with recent structural studies, this indicates that conformational changes in GroEL14 following the dissociation of GroES7 must precede ADP release. These results explain how the GroEL14 cavity can become reversibly accessible to proteins under in vivo conditions that favor 2:1 complexes. (+info)
The role of DnaK/DnaJ and GroEL/GroES systems in the removal of endogenous proteins aggregated by heat-shock from Escherichia coli cells.
The submission of Escherichia coli cells to heat-shock (45 degrees C, 15 min) caused the intracellular aggregation of endogenous proteins. In the wt cells the aggregates (the S fraction) disappeared 10 min after transfer to 37 degrees C. In contrast, the S fraction in the dnaK and dnaJ mutant strains was stable during approximately one generation time (45 min). This demonstrated that neither the renaturation nor the degradation of the denatured proteins was possible in the absence of DnaK and DnaJ. The groEL44 and groES619 mutations stabilised the aggregates to a lesser extent. It was shown by the use of cloned genes, dnaK/dnaJ or groEL/groES, producing the corresponding proteins in about 4-fold excess, that the appearance of the S fraction in the wt strain resulted from a transiently insufficient supply of the heat-shock proteins. Overproduction of the GroEL/GroES proteins in dnaK756 or dnaJ259 background prevented the aggregation, however, overproduction of the DnaK/DnaJ proteins did not prevent the aggregation in the groEL44 or groES619 mutant cells although it accelerated the disappearance of the aggregates. The properties of the aggregated proteins are discussed from the point of view of their competence to renaturation/degradation by the heat-shock system. (+info)
GroEL/GroES-dependent reconstitution of alpha2 beta2 tetramers of humanmitochondrial branched chain alpha-ketoacid decarboxylase. Obligatory interaction of chaperonins with an alpha beta dimeric intermediate.
The decarboxylase component (E1) of the human mitochondrial branched chain alpha-ketoacid dehydrogenase multienzyme complex (approximately 4-5 x 10(3) kDa) is a thiamine pyrophosphate-dependent enzyme, comprising two 45.5-kDa alpha subunits and two 37.8-kDa beta subunits. In the present study, His6-tagged E1 alpha2 beta2 tetramers (171 kDa) denatured in 8 M urea were competently reconstituted in vitro at 23 degrees C with an absolute requirement for chaperonins GroEL/GroES and Mg-ATP. Unexpectedly, the kinetics for the recovery of E1 activity was very slow with a rate constant of 290 M-1 s-1. Renaturation of E1 with a similarly slow kinetics was also achieved using individual GroEL-alpha and GroEL-beta complexes as combined substrates. However, the beta subunit was markedly more prone to misfolding than the alpha in the absence of GroEL. The alpha subunit was released as soluble monomers from the GroEL-alpha complex alone in the presence of GroES and Mg-ATP. In contrast, the beta subunit discharged from the GroEL-beta complex readily rebound to GroEL when the alpha subunit was absent. Analysis of the assembly state showed that the His6-alpha and beta subunits released from corresponding GroEL-polypeptide complexes assembled into a highly structured but inactive 85.5-kDa alpha beta dimeric intermediate, which subsequently dimerized to produce the active alpha2 beta2 tetrameter. The purified alpha beta dimer isolated from Escherichia coli lysates was capable of binding to GroEL to produce a stable GroEL-alpha beta ternary complex. Incubation of this novel ternary complex with GroES and Mg-ATP resulted in recovery of E1 activity, which also followed slow kinetics with a rate constant of 138 M-1 s-1. Dimers were regenerated from the GroEL-alpha beta complex, but they needed to interact with GroEL/GroES again, thereby perpetuating the cycle until the conversion from dimers to tetramers was complete. Our study describes an obligatory role of chaperonins in priming the dimeric intermediate for subsequent tetrameric assembly, which is a slow step in the reconstitution of E1 alpha2 beta2 tetramers. (+info)
Mechanisms for GroEL/GroES-mediated folding of a large 86-kDa fusion polypeptide in vitro.
Our understanding of mechanisms for GroEL/GroES-assisted protein folding to date has been derived mostly from studies with small proteins. Little is known concerning the interaction of these chaperonins with large multidomain polypeptides during folding. In the present study, we investigated chaperonin-dependent folding of a large 86-kDa fusion polypeptide, in which the mature maltose-binding protein (MBP) sequence was linked to the N terminus of the alpha subunit of the decarboxylase (E1) component of the human mitochondrial branched-chain alpha-ketoacid dehydrogenase complex. The fusion polypeptide, MBP-alpha, when co-expressed with the beta subunit of E1, produced a chimeric protein MBP-E1 with an (MBP-alpha)2beta2 structure, similar to the alpha2 beta2 structure in native E1. Reactivation of MBP-E1 denatured in 8 M urea was absolutely dependent on GroEL/GroES and Mg2+-ATP, and exhibited strikingly slow kinetics with a rate constant of 376 M-1 s-1, analogous to denatured untagged E1. Chaperonin-mediated refolding of the MBP-alpha fusion polypeptide showed that the folding of the MBP moiety was about 7-fold faster than that of the alpha moiety on the same chain with rate constants of 1.9 x 10(-3) s-1 and 2.95 x 10(-4) s-1, respectively. This explained the occurrence of an MBP-alpha. GroEL binary complex that was isolated with amylose resin from the refolding mixture and transformed Escherichia coli lysates. The data support the thesis that distinct functional sequences in a large polypeptide exhibit different folding characteristics on the same GroEL scaffold. Moreover, we show that when the alpha.GroEL complex (molar ratio 1:1) was incubated with GroES, the latter was capable of capping either the very ring that harbored the 48-kDa (His)6-alpha polypeptide (in cis) or the opposite unoccupied cavity (in trans). In contrast, the MBP-alpha.GroEL (1:1) complex was capped by GroES exclusively in the trans configuration. These findings suggest that the productive folding of a large multidomain polypeptide can only occur in the GroEL cavity that is not sequestered by GroES. (+info)
Presence of a pre-apoptotic complex of pro-caspase-3, Hsp60 and Hsp10 in the mitochondrial fraction of jurkat cells.
Activation of pro-caspase-3 is a central event in the execution phase of apoptosis and appears to serve as the convergence point of different apoptotic signaling pathways. Recently, mitochondria were found to play a central role in apoptosis through release of cytochrome c and activation of caspases. Moreover, a sub-population of pro-caspase-3 has been found to be localized to this organelle. In the present study, we demonstrate that pro-caspase-3 is present in the mitochondrial fraction of Jurkat T cells in a complex with the chaperone proteins Hsp60 and Hsp10. Induction of apoptosis with staurosporine led to the activation of mitochondrial pro-caspase-3 and its dissociation from the Hsps which were released from mitochondria. The release of Hsps occurred simultaneously with the release of other mitochondrial intermembrane space proteins including cytochrome c and adenylate kinase, prior to a loss of mitochondrial transmembrane potential. In in vitro systems, recombinant Hsp60 and Hsp10 accelerated the activation of pro-caspase-3 by cytochrome c and dATP in an ATP-dependent manner, consistent with their function as chaperones. This finding suggests that the release of mitochondrial Hsps may also accelerate caspase activation in the cytoplasm of intact cells. (+info)
Chaperonin function: folding by forced unfolding.
The ability of the GroEL chaperonin to unfold a protein trapped in a misfolded condition was detected and studied by hydrogen exchange. The GroEL-induced unfolding of its substrate protein is only partial, requires the complete chaperonin system, and is accomplished within the 13 seconds required for a single system turnover. The binding of nucleoside triphosphate provides the energy for a single unfolding event; multiple turnovers require adenosine triphosphate hydrolysis. The substrate protein is released on each turnover even if it has not yet refolded to the native state. These results suggest that GroEL helps partly folded but blocked proteins to fold by causing them first to partially unfold. The structure of GroEL seems well suited to generate the nonspecific mechanical stretching force required for forceful protein unfolding. (+info)
GroEL-GroES cycling: ATP and nonnative polypeptide direct alternation of folding-active rings.
The double-ring chaperonin GroEL mediates protein folding in the central cavity of a ring bound by ATP and GroES, but it is unclear how GroEL cycles from one folding-active complex to the next. We observe that hydrolysis of ATP within the cis ring must occur before either nonnative polypeptide or GroES can bind to the trans ring, and this is associated with reorientation of the trans ring apical domains. Subsequently, formation of a new cis-ternary complex proceeds on the open trans ring with polypeptide binding first, which stimulates the ATP-dependent dissociation of the cis complex (by 20- to 50-fold), followed by GroES binding. These results indicate that, in the presence of nonnative protein, GroEL alternates its rings as folding-active cis complexes, expending only one round of seven ATPs per folding cycle. (+info)
Previously undetected Chlamydia trachomatis infection, immunity to heat shock proteins and tubal occlusion in women undergoing in-vitro fertilization.
The relationship between a previously undetected Chlamydia trachomatis infection, tubal infertility, immunity to heat shock proteins and subsequent in-vitro fertilization (IVF) outcome was evaluated. Women with tubal occlusion, with or without hydrosalpinges, and no history of C. trachomatis infection were tested for circulating antibodies to the human 60-kDa heat shock protein (Hhsp60), the C. trachomatis 10-kDa heat shock protein (Chsp10) and C. trachomatis surface antigens prior to their initial IVF cycle. Sera were obtained from 50 women whose male partners were infertile, 58 women with tubal occlusion but no hydrosalpinx and 39 women with tubal occlusions plus hydrosalpinx. Clinical pregnancies were documented in 68% of the women with male factor infertility. This was higher than the 43.1% rate in women with tubal occlusions (P = 0.04) and the 41% rate in women with hydrosalpinx (P = 0.02). C. trachomatis antibodies were present in one (2%) women with male factor infertility as opposed to 15 (25.9%) women with tubal occlusion (P = 0.003) and 13 (33%) with hydrosalpinx (P < 0.0001). Antibodies to Chsp10 were more prevalent in women with hydrosalpinx (46.8%) than in women with male factor infertility (P < 0.0001, 6%) or tubal occlusion (P = 0.0009, 15.5%). Hhsp60 antibodies were equally more prevalent in women with tubal occlusion plus (46.8%) or minus hydrosalpinx (41.4%) than in women with male factor infertility (P < 0.0002). Hhsp60 was more prevalent in those women positive for Chsp10 (P = 0.02) or C. trachomatis (P = 0.04) antibodies than in women lacking these antibodies. There was no relationship between any of the antibodies measured in sera and IVF outcome. (+info)