Mammalian mitochondrial chaperonin 60 functions as a single toroidal ring

A spatial portrait of the human sebaceous gland transcriptional program

Sebaceous glands (SG) and their oily secretion (sebum) are indispensable for maintaining skin structure and function, and their deregulation causes skin disorders including but not limited to acne. Recent studies also indicate that sebum may have important immunomodulatory activities and may influence whole-body energy metabolism. However, the progressive transcriptional changes of sebocytes that lead to sebum production have never been characterized in detail. Here, we exploited the high cellular resolution provided by sebaceous hyperplasia and integrated spatial transcriptomics, pseudo time analysis, RNA velocity, and functional enrichment to map the landscape of sebaceous differentiation. Our results were validated by comparison with published SG transcriptome data and further corroborated by assessing the protein expression pattern of a subset of the transcripts in the public repository Human Protein Atlas. Departing from four sebocyte differentiation stages generated by unsupervised clustering, we demonstrate consecutive modulation of cellular functions associable with specific gene sets, from cell proliferation and oxidative phosphorylation via lipid synthesis to cell death. Both validation methods confirmed the biological significance of our results. Our report is complemented by a freely available and browsable online tool. Our data provide the first high-resolution spatial portrait of the SG transcriptional landscape and deliver starting points for experimentally assessing novel candidate molecules for regulating SG homeostasis in health and disease.

Cryo-EM structure and molecular dynamic simulations explain the enhanced stability and ATP activity of the pathological chaperonin mutant

Chaperonins Hsp60s are required for cellular vitality by assisting protein folding in an ATP-dependent mechanism. Although conserved, the human mitochondrial mHsp60 exhibits molecular characteristics distinct from the E. coli GroEL, with different conformational assembly and higher subunit association dynamics, suggesting a different mechanism. We previously found that the pathological mutant mHsp60V72I exhibits enhanced subunit association stability and ATPase activity. To provide structural explanations for the V72I mutational effects, here we determined a cryo-EM structure of mHsp60V72I. Our structural analysis combined with molecular dynamic simulations showed mHsp60V72I with increased inter-subunit interface, binding free energy, and dissociation force, all contributing to its enhanced subunit association stability. The gate to the nucleotide-binding (NB) site in mHsp60V72I mimicked the open conformation in the nucleotide-bound state with an additional open channel leading to the NB site, both promoting the mutant's ATPase activity. Our studies highlight the importance of mHsp60's characteristics in its biological function.

Crystal structures of dimeric and heptameric mtHsp60 reveal the mechanism of chaperonin inactivation

Mitochondrial Hsp60 (mtHsp60) plays a crucial role in maintaining the proper folding of proteins in the mitochondria. mtHsp60 self-assembles into a ring-shaped heptamer, which can further form a double-ring tetradecamer in the presence of ATP and mtHsp10. However, mtHsp60 tends to dissociate in vitro, unlike its prokaryotic homologue, GroEL. The molecular structure of dissociated mtHsp60 and the mechanism behind its dissociation remain unclear. In this study, we demonstrated that Epinephelus coioides mtHsp60 (EcHsp60) can form a dimeric structure with inactive ATPase activity. The crystal structure of this dimer reveals symmetrical subunit interactions and a rearranged equatorial domain. The α4 helix of each subunit extends and interacts with its adjacent subunit, leading to the disruption of the ATP-binding pocket. Furthermore, an RLK motif in the apical domain contributes to stabilizing the dimeric complex. These structural and biochemical findings provide new insights into the conformational transitions and functional regulation of this ancient chaperonin.

Asymmetric apical domain states of mitochondrial Hsp60 coordinate substrate engagement and chaperonin assembly

The mitochondrial chaperonin, mtHsp60, promotes the folding of newly imported and transiently misfolded proteins in the mitochondrial matrix, assisted by its co-chaperone mtHsp10. Despite its essential role in mitochondrial proteostasis, structural insights into how this chaperonin binds to clients and progresses through its ATP-dependent reaction cycle are not clear. Here, we determined cryo-electron microscopy (cryo-EM) structures of a hyperstable disease-associated mtHsp60 mutant, V72I, at three stages in this cycle. Unexpectedly, client density is identified in all states, revealing interactions with mtHsp60's apical domains and C-termini that coordinate client positioning in the folding chamber. We further identify a striking asymmetric arrangement of the apical domains in the ATP state, in which an alternating up/down configuration positions interaction surfaces for simultaneous recruitment of mtHsp10 and client retention. Client is then fully encapsulated in mtHsp60/mtHsp10, revealing prominent contacts at two discrete sites that potentially support maturation. These results identify a new role for the apical domains in coordinating client capture and progression through the cycle, and suggest a conserved mechanism of group I chaperonin function.

Hereditary spastic paraplegia SPG13 mutation increases structural stability and ATPase activity of human mitochondrial chaperonin

Human mitochondrial chaperonin mHsp60 is broadly associated with various human health conditions and the V72I mutation in mHsp60 causes a form of hereditary spastic paraplegia, a neurodegenerative disease. The main function of mHsp60 is to assist folding of mitochondrial proteins in an ATP-dependent manner. In this study, we unexpectedly found that mutant mHsp60^V72I was more stable structurally and more active in the ATPase activity than the wildtype. Analysis of our recently solved cryo-EM structure of mHsp60 revealed allosteric roles of V72I in structural stability and ATPase activity, which were supported by studies including those using the V72A mutation. Despite with the increases in structural stability and ATPase activity, mHsp60^V72I was less efficient in folding malate dehydrogenase, a putative mHsp60 substrate protein in mitochondria and also commonly used in chaperonin studies. In addition, although mHsp60^V72I along with its cochaperonin mHsp10 was able to substitute the E. coli chaperonin system in supporting cell growth under normal temperature of 37 °C, it was unable under heat shock temperature of 42 °C. Our results support the importance of structural dynamics and an optimal ATP turnover that mHsp60 has evolved for its function and physiology. We propose that unproductive energy utilization, or hyperactive ATPase activity and compromised folding function, not mutually exclusive, are responsible for the V72I pathology in neurodegenerative disease.

Unveiling the mechanism of action of nature-inspired anti-cancer compounds using a multi-omics approach

The 2020 global cancer registry has ranked breast cancer (BCa) as the most commonly diagnosed type of cancer and the most common cause of cancer-related deaths in women worldwide. Increasing resistance and significant side effects continue to limit the efficacy of anti-BCa drugs, hence the need to identify new drug targets and to develop novel compounds to overcome these limitations. Nature-inspired anti-cancer compounds are becoming increasingly popular since they often provide a relatively safe and effective alternative. In this study, we employed multi-omics techniques to gain insights into the relevant mechanism of action of two recently identified new nature-inspired anti-cancer compounds (SIMR3066 and SIMR3058). Discovery proteomics analysis combined with LC-MS/MS-based untargeted metabolomics analysis was performed on compound-treated vs DMSO-treated (control) MCF-7 cells. Downstream protein functional enrichment analysis showed that most of the responsive proteins were functionally associated with antigen processing and neutrophil degranulation, RNA catabolism and protein folding as well as cytoplasmic vesicle lumen and mitochondrial matrix formation. Consistent with the proteomics findings, metabolomic pathway analysis suggested that the differentially abundant compounds indicated altered metabolic pathways such as glycolysis, the Krebs cycle and oxidative phosphorylation. Furthermore, metabolomics-based enriched-for-action pathway analysis showed that the two compounds associate with mercaptopurine, thioguanine and azathioprine related pathways. Lastly, integrated proteomics and metabolomics analysis revealed that treatment of BCa with SIMR3066 disrupts several signaling pathways including p53-mediated apoptosis and the circadian entertainment pathway. Overall, the multi-omics approach we used in this study indicated that it is a powerful tool in probing the mechanism of action of lead drug candidates. SIGNIFICANCE: In this study we adopted a multi-omics (proteomics and metabolomics) strategy to learn more about the molecular mechanisms of action of nature-inspired potential anticancer drugs. Following treatment with SIMR3066 or SIMR3058, the integration of these multi-omics data sets revealed which biological pathways are altered in BCa cells. This study demonstrates that combining proteomics with metabolomics is a powerful method to investigate the mechanism of action of potential anticancer lead drug candidates.

Conserved and divergent chaperoning effects of Hsp60/10 chaperonins on protein folding landscapes

The GroEL/ES chaperonin cavity surface charge properties, especially the negative charges, play an important role in its capacity to assist intracavity protein folding. Remarkably, the larger fraction of GroEL/ES negative charges are not conserved among different bacterial species, resulting in a large variation in negative-charge density in the GroEL/ES cavity across prokaryotes. Intriguingly, eukaryotic GroEL/ES homologs have the lowest negative-charge density in the chaperonin cavity. This prompted us to investigate if GroEL’s chaperoning mechanism changed during evolution. Using a model in vivo GroEL/ES substrate, we show that the ability of GroEL/ES to buffer entropic traps in the folding pathway of its substrate was partially dependent upon the negative-charge density inside its cavity. While this activity of GroEL/ES was found to be essential for Escherichia coli, it has been perfected in some organisms and diminished in others. However, irrespective of their charges, all the tested homologs retained their ability to regulate polypeptide chain collapse and remove enthalpic traps from folding pathways. The ability of these GroEL/ES homologs to buffer mutational variations in a model substrate correlated with their negative-charge density. Thus, Hsp60/10 chaperonins in different organisms may have changed to accommodate a different spectrum of mutations on their substrates.

Structural and Functional Features of Viral Chaperonins

Chaperonins provide proper folding of proteins in vivo and in vitro and, as was thought until recently, are characteristic of prokaryotes, eukaryotes, and archaea. However, it turned out that some bacteria viruses (bacteriophages) encode their own chaperonins. This review presents results of the investigations of the first representatives of this new chaperonin group: the double-ring EL chaperonin and the single-ring OBP and AR9 chaperonins. Biochemical properties and structure of the phage chaperonins were compared within the group and with other known group I and group II chaperonins.

Structural Alternation in Heat Shock Proteins of Activated Macrophages

The inflammatory response of macrophages is an orderly and complex process under strict regulation accompanied by drastic changes in morphology and functions. It is predicted that proteins will undergo structural changes during these finely regulated processes. However, changes in structural proteome in macrophages during the inflammatory response remain poorly characterized. In the present study, we applied limited proteolysis coupled mass spectrometry (LiP-MS) to identify proteome-wide structural changes in lipopolysaccharide (LPS)-activated macrophages. We identified 386 structure-specific proteolytic fingerprints from 230 proteins. Using the Gene Ontology (GO) biological process enrichment, we discovered that proteins with altered structures were enriched into protein folding-related terms, in which HSP60 was ranked as the most changed protein. We verified the structural changes in HSP60 by using cellular thermal shift assay (CETSA) and native CETSA. Our results showed that the thermal stability of HSP60 was enhanced in activated macrophages and formed an HSP10-less complex. In conclusion, we demonstrate that in situ structural systems biology is an effective method to characterize proteomic structural changes and reveal that the structures of chaperone proteins vary significantly during macrophage activation.

Structural basis for the structural dynamics of human mitochondrial chaperonin mHsp60

Human mitochondrial chaperonin mHsp60 is essential for mitochondrial function by assisting folding of mitochondrial proteins. Unlike the double-ring bacterial GroEL, mHsp60 exists as a heptameric ring that is unstable and dissociates to subunits. The structural dynamics has been implicated for a unique mechanism of mHsp60. We purified active heptameric mHsp60, and determined a cryo-EM structure of mHsp60 heptamer at 3.4 Å. Of the three domains, the equatorial domains contribute most to the inter-subunit interactions, which include a four-stranded β sheet. Our structural comparison with GroEL shows that mHsp60 contains several unique sequences that directly decrease the sidechain interactions around the β sheet and indirectly shorten β strands by disengaging the backbones of the flanking residues from hydrogen bonding in the β strand conformation. The decreased inter-subunit interactions result in a small inter-subunit interface in mHsp60 compared to GroEL, providing a structural basis for the dynamics of mHsp60 subunit association. Importantly, the unique sequences are conserved among higher eukaryotic mitochondrial chaperonins, suggesting the importance of structural dynamics for eukaryotic chaperonins. Our structural comparison with the single-ring mHsp60-mHsp10 shows that upon mHsp10 binding the shortened inter-subunit β sheet is restored and the overall inter-subunit interface of mHsp60 increases drastically. Our structural basis for the mHsp10 induced stabilization of mHsp60 subunit interaction is consistent with the literature that mHsp10 stabilizes mHsp60 quaternary structure. Together, our studies provide structural bases for structural dynamics of the mHsp60 heptamer and for the stabilizing effect of mHsp10 on mHsp60 subunit association.

Exploring the aging effect of the anticancer drugs doxorubicin and mitoxantrone on cardiac mitochondrial proteome using a murine model

Current cancer therapies are successfully increasing the lifespan of cancer patients. Nevertheless, cardiotoxicity is a serious chemotherapy-induced adverse side effect. Doxorubicin (DOX) and mitoxantrone (MTX) are cardiotoxic anticancer agents, whose toxicological mechanisms are still to be identified. This study focused on DOX and MTX's cardiac mitochondrial damage and their molecular mechanisms. As a hypothesis, we also sought to compare the cardiac modulation caused by 9 mg/kg of DOX or 6 mg/kg of MTX in young adult mice (3 months old) with old control mice (aged control, 18-20 months old) to determine if DOX- and MTX-induced damage had common links with the aging process. Cardiac homogenates and enriched mitochondrial fractions were prepared from treated and control animals and analyzed by immunoblotting and enzymatic assays. Enriched mitochondrial fractions were also characterized by mass spectrometry-based proteomics. Data obtained showed a decrease in mitochondrial density in young adults treated with DOX or MTX and aged control, as assessed by citrate synthase (CS) activity. Furthermore, aged control had increased expression of the peroxisome proliferator-activated receptor γ coactivator 1 α (PGC1α) and manganese superoxide dismutase (MnSOD). Regarding the enriched mitochondrial fractions, DOX and MTX led to downregulation of proteins related to oxidative phosphorylation, fatty acid oxidation, amino acid metabolic process, and tricarboxylic acid cycle. MTX had a greater impact on malate dehydrogenase (MDH2) and pyruvate dehydrogenase E1 component subunit α (PDHA1). No significant proteomic changes were observed in the enriched mitochondrial fractions of aged control when compared to young control. To conclude, DOX and MTX promoted changes in several mitochondrial-related proteins in young adult mice, but none resembling the aged phenotype.

Cryo-EM structure of human mitochondrial HSPD1

Chaperonins play an important role in folding newly synthesized or translocated proteins in all organisms. The bacterial chaperonin GroEL has served as a model system for the understanding of these proteins. In comparison, its human homolog, known as mitochondrial heat shock protein family member D1 (HSPD1) is poorly understood. Here, we present the structure of HSPD1 in the apo state determined by cryo-electron microscopy (cryo-EM). Unlike GroEL, HSPD1 forms mostly single ring assemblies in the absence of co-chaperonin (HSPE1). Comparison with GroEL shows a rotation and increased flexibility of the apical domain. Together with published structures of the HSPD1/HSPE1 co-chaperonin complex, this work gives insight into the structural changes that occur during the catalytic cycle. This new understanding of HSPD1 structure and its rearrangements upon complex formation may provide new insights for the development of HSPD1-targeting treatments against a diverse range of diseases including glioblastoma.

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First cryo-EM structure of the apo HSPD1 chaperone complex

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Mass spectrometry has shown the presence of 7, 8, 15, and 16-mers of HSPD-1

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In addition to a single ring, HSPD-1 can form an unusual inverted ring architecture

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Describe grid preparation conditions that alleviate preferred orientation

Function and Fiber-Type Specific Distribution of Hsp60 and αB-Crystallin in Skeletal Muscles: Role of Physical Exercise

Simple Summary

Skeletal muscle represents about 40% of the body mass in humans and it is a copious and plastic tissue, rich in proteins that are subject to continuous rearrangements. Physical exercise is considered a physiological stressor for different organs, in particular for skeletal muscle, and it is a factor able to stimulate the cellular remodeling processes related to the phenomenon of adaptation. All cells respond to various stress conditions by up-regulating the expression and/or activation of a group of proteins called heat shock proteins (HSPs). Although their expression is induced by several stimuli, they are commonly recognized as HSPs due to the first experiments showing their increased transcription after application of heat shock. These proteins are molecular chaperones mainly involved in assisting protein transport and folding, assembling multimolecular complexes, and triggering protein degradation by proteasome. Among the HSPs, a special attention needs to be devoted to Hsp60 and αB-crystallin, proteins constitutively expressed in the skeletal muscle, where they are known to be important in muscle physiopathology. Therefore, here we provide a critical update on their role in skeletal muscle fibers after physical exercise, highlighting the control of their expression, their biological function, and their specific distribution within skeletal muscle fiber-types.

Abstract

Skeletal muscle is a plastic and complex tissue, rich in proteins that are subject to continuous rearrangements. Skeletal muscle homeostasis can be affected by different types of stresses, including physical activity, a physiological stressor able to stimulate a robust increase in different heat shock proteins (HSPs). The modulation of these proteins appears to be fundamental in facilitating the cellular remodeling processes related to the phenomenon of training adaptations such as hypertrophy, increased oxidative capacity, and mitochondrial activity. Among the HSPs, a special attention needs to be devoted to Hsp60 and αB-crystallin (CRYAB), proteins constitutively expressed in the skeletal muscle, where their specific features could be highly relevant in understanding the impact of different volumes of training regimes on myofiber types and in explaining the complex picture of exercise-induced mechanical strain and damaging conditions on fiber population. This knowledge could lead to a better personalization of training protocols with an optimal non-harmful workload in populations of individuals with different needs and healthy status. Here, we introduce for the first time to the reader these peculiar HSPs from the perspective of exercise response, highlighting the control of their expression, biological function, and specific distribution within skeletal muscle fiber-types.

Complex Destabilization in the Mitochondrial Chaperonin Hsp60 Leads to Disease

Several neurological disorders have been linked to mutations in chaperonin genes and more specifically to the HSPD1 gene. In humans, HSPD1 encodes the mitochondrial Heat Shock Protein 60 (mtHsp60) chaperonin, which carries out essential protein folding reactions that help maintain mitochondrial and cellular homeostasis. It functions as a macromolecular complex that provides client proteins an environment that favors proper folding in an ATP-dependent manner. It has been established that mtHsp60 plays a crucial role in the proper folding of mitochondrial proteins involved in ATP producing pathways. Recently, various single-point mutations in the mtHsp60 encoding gene have been directly linked to neuropathies and paraplegias. Individuals who harbor mtHsp60 mutations that negatively impact its folding ability display phenotypes with highly compromised muscle and neuron cells. Carriers of these mutations usually develop neuropathies and paraplegias at different stages of their lives mainly characterized by leg stiffness and weakness as well as degeneration of spinal cord nerves. These phenotypes are likely due to hindered energy producing pathways involved in cellular respiration resulting in ATP deprived cells. Although the complete protein folding mechanism of mtHsp60 is not well understood, recent work suggests that several of these mutations act by destabilizing the oligomeric stability of mtHsp60. Here, we discuss recent studies that highlight key aspects of the mtHsp60 mechanism with a focus on some of the known disease-causing point mutations, D29G and V98I, and their effect on the protein folding reaction cycle.

EMDIP: An Entropy Measure to Discover Important Proteins in PPI networks

Discovering important proteins in Protein-Protein Interaction (PPI) networks has attracted a lot of attention in recent years. Most of the previous work applies different network centrality measures such as Closeness, Betweenness, PageRank and many others to discover the most influential proteins in PPI networks. Although entropy is a well-known graph-based method in computer science, according to our knowledge, it is not used in the biology domain for this purpose. In this paper, first, we annotate the human PPI network with available annotation data. Second, we introduce a new concept called annotation-context that describes each protein according to annotation data of its neighbors. Third, we apply an entropy measure to discover proteins with varied annotation-context. Empirical results indicate that our proposed method succeeded in (1) differentiating essential and non-essential proteins in PPI networks with annotation data; (2) outperforming centrality measures in the task of discovering essential nodes; (3) predicting new annotated proteins based on existing annotation data.

Chaperonin-assisted protein folding: a chronologue

This chronologue seeks to document the discovery and development of an understanding of oligomeric ring protein assemblies known as chaperonins that assist protein folding in the cell. It provides detail regarding genetic, physiologic, biochemical, and biophysical studies of these ATP-utilizing machines from both in vivo and in vitro observations. The chronologue is organized into various topics of physiology and mechanism, for each of which a chronologic order is generally followed. The text is liberally illustrated to provide firsthand inspection of the key pieces of experimental data that propelled this field. Because of the length and depth of this piece, the use of the outline as a guide for selected reading is encouraged, but it should also be of help in pursuing the text in direct order.

Exogenous 10 kDa-Heat Shock Protein Preserves Mitochondrial Function After Hypoxia/Reoxygenation

Humoral factors released during ischemic preconditioning (IPC) protect the myocardium against ischemia/reperfusion (I/R) injury. We have recently identified 10 kDa-heat shock protein (HSP10) and a fraction of small 5-10 kDa peptides (5-10-sP) in the coronary effluent of IPC-treated hearts and demonstrated their cardioprotective potential. We here used our isolated mitochondria model to characterize the impact of exogenous HSP10 and 5-10-sP on mitochondria function from myocardium subjected to I/R injury. Isolated perfused rat hearts were submitted to 30-min global ischemia and 10-min reperfusion. Before ischemia, isolated hearts were infused with saline or 5-10-sP, with or without a mitochondrial ATP-sensitive-K⁺-channel blocker (5HD 10 μmol·L^-1) or PKC inhibitor (chelerythrine 10 μmol·L^-1), before I/R. HSP10 (1 µmol·L^-1) was infused into isolated hearts before I/R without blockers. At 10-min reperfusion, the mitochondria were isolated and mitochondrial function was assessed. In a subset of experiments, freshly isolated mitochondria were directly incubated with HSP10 or 5-10-sP with or without 5HD or chelerythrine before in vitro hypoxia/reoxygenation. Infusion of 5-10-sP (n = 5) and HSP10 (n = 5) into isolated hearts before I/R improved mitochondrial ADP-stimulated respiration, ATP production and prevented mitochondrial ROS formation compared to the I/R group (n = 5); this effect was abrogated by 5HD and chelerythrine. In freshly isolated mitochondria with in vitro hypoxia/reoxygenation, HSP10 (n = 16) and 5-10-sP (n = 16) incubation prevented reductions of mitochondrial ADP-stimulated respiration (91.5 ± 5.1 nmol O2/min/mg PTN), ATP production (250.1 ± 9.3 μmol ATP/200μg PTN), and prevented mitochondrial ROS production (219.7 ± 9.0 nmol H2O2/200μg PTN) induced by hypoxia/reoxygenation (n = 12, 51.5 ± 5.0 nmol O2/min/mg PTN; 187 ± 21.7 μmol ATP/200 μg PTN; 339.0 ± 14.3 nmol H2O2/200 μg PTN, p < 0.001, respectively). 5HD reduced the ADP-stimulated respiration in the HSP10 group (65.84 ± 3.3 nmol O2/min/mg PTN), ATP production (193.7 ± 12.1 μmol ATP/200μg PTN) and increased ROS in the 5-10-sP group (274.4 ± 21.7 nmol H2O2/200 μg PTN). Mitochondria are a target of the cardioprotection induced by 5-10-sP and HSP10. This protection is dependent of PKC and mK_ATP activation. HSP10 can act directly on mitochondria and protects against hypoxia/reoxygenation injury by mK_ATP activation.

MitCHAP-60 and Hereditary Spastic Paraplegia SPG-13 Arise from an Inactive hsp60 Chaperonin that Fails to Fold the ATP Synthase β-Subunit

The human mitochondrial heat shock protein 60 (hsp60) is a tetradecameric chaperonin that folds proteins in the mitochondrial matrix. An hsp60 D3G mutation leads to MitCHAP-60, an early onset neurodegenerative disease while hsp60 V72I has been linked to SPG13, a form of hereditary spastic paraplegia. Previous studies have suggested that these mutations impair the protein folding activity of hsp60 complexes but the detailed mechanism by which these mutations lead the neuromuscular diseases remains unknown. It is known, is that the β-subunit of the human mitochondrial ATP synthase co-immunoprecipitates with hsp60 indicating that the β-subunit is likely a substrate for the chaperonin. Therefore, we hypothesized that hsp60 mutations cause misfolding of proteins that are critical for aerobic respiration. Negative-stain electron microscopy and DLS results suggest that the D3G and V72I complexes fall apart when treated with ATP or ADP and are therefore unable to fold denatured substrates such as α-lactalbumin, malate dehydrogenase (MDH), and the β-subunit of ATP synthase in in-vitro protein-folding assays. These data suggests that hsp60 plays a crucial role in folding important players in aerobic respiration such as the β-subunit of the ATP synthase. The hsp60 mutations D3G and V72I impair its ability to fold mitochondrial substrates leading to abnormal ATP synthesis and the development of the MitCHAP-60 and SPG13 neuromuscular degenerative disorders.

Inhibition of Aβ1-42 Fibrillation by Chaperonins: Human Hsp60 Is a Stronger Inhibitor than Its Bacterial Homologue GroEL

Alzheimer's disease is a chronic neurodegenerative disease characterized by the accumulation of pathological aggregates of amyloid beta peptide. Many efforts have been focused on understanding peptide aggregation pathways and on identification of molecules able to inhibit aggregation in order to find an effective therapy. As a result, interest in neuroprotective proteins, such as molecular chaperones, has increased as their normal function is to assist in protein folding or to facilitate the disaggregation and/or clearance of abnormal aggregate proteins. Using biophysical techniques, we evaluated the effects of two chaperones, human Hsp60 and bacterial GroEL, on the fibrillogenesis of Aβ_1-42. Both chaperonins interfere with Aβ_1-42 aggregation, but the effect of Hsp60 is more significant and correlates with its more pronounced flexibility and stronger interaction with ANS, an indicator of hydrophobic regions. Dose-dependent ThT fluorescence kinetics and SAXS experiments reveal that Hsp60 does not change the nature of the molecular processes stochastically leading to the formation of seeds, but strongly delays them by recognition of hydrophobic sites of some peptide species crucial for triggering amyloid formation. Hsp60 reduces the initial chaotic heterogeneity of Aβ_1-42 sample at high concentration regimes. The understanding of chaperone action in counteracting pathological aggregation could be a starting point for potential new therapeutic strategies against neurodegenerative diseases.

GroEL and the GroEL-GroES Complex

Chaperonin is categorized as a molecular chaperone and mediates the formation of the native conformation of proteins by first preventing folding during synthesis or membrane translocation and subsequently by mediating the step-wise ATP-dependent release that result in proper folding. In the GroEL-GroES complex, a single heptameric GroEL ring binds one GroES ring in the presence of ATP/ADP, in this vein, the double ring GroEL tetradecamer is present in two distinct types of GroEL-GroES complexes: asymmetric 1:1 "bullet"-shaped GroEL:GroES and symmetric 1:2 "football" (American football)-shaped GroEL:GroES₂. There have been debates as to which complex is critical to the productive protein folding mediated by the GroEL-GroES complex, and how GroES coordinates with GroEL in the chaperonin reaction cycle in association with regulation by adenine nucleotides and through the interplay of substrate proteins. A lot of knowledge on chaperonins has been accumulating as if expanding as ripples spread around the GroEL-GroES from Escherichia coli. In this article, an overview is presented on GroEL and the GroEL-GroES complex, with emphasis on their morphological variations, and some potential applications to the fabrication of nanocomposites using GroEL as a nano-block. In parallel, a guideline is presented that supports the recognition that the E. coli and its GroEL-GroES complex do not always receive in standard literature because the biochemical features of chaperonins derived from others special, such as mammals, are not always the same as those confirmed using GroEL-GroES derived from E. coli.

Implications of the mitochondrial interactome of mammalian thioredoxin 2 for normal cellular function and disease

Multiple thioredoxin isoforms exist in all living cells. To explore the possible functions of mammalian mitochondrial thioredoxin 2 (Trx2), an interactome of mouse Trx2 was initially created using (i) a monothiol mouse Trx2 species for capturing protein partners from different organs and (ii) yeast two hybrid screens on human liver and rat brain cDNA libraries. The resulting interactome consisted of 195 proteins (Trx2 included) plus the mitochondrial 16S RNA. 48 of these proteins were classified as mitochondrial (MitoCarta2.0 human inventory). In a second step, the mouse interactome was combined with the current four-membered mitochondrial sub-network of human Trx2 (BioGRID) to give a 53-membered human Trx2 mitochondrial interactome (52 interactor proteins plus the mitochondrial 16S RNA). Although thioredoxins are thiol-employing disulfide oxidoreductases, approximately half of the detected interactions were not due to covalent disulfide bonds. This finding reinstates the extended role of thioredoxins as moderators of protein function by specific non-covalent, protein-protein interactions. Analysis of the mitochondrial interactome suggested that human Trx2 was involved potentially in mitochondrial integrity, formation of iron sulfur clusters, detoxification of aldehydes, mitoribosome assembly and protein synthesis, protein folding, ADP ribosylation, amino acid and lipid metabolism, glycolysis, the TCA cycle and the electron transport chain. The oxidoreductase functions of Trx2 were verified by its detected interactions with mitochondrial peroxiredoxins and methionine sulfoxide reductase. Parkinson's disease, triosephosphate isomerase deficiency, combined oxidative phosphorylation deficiency, and lactate dehydrogenase b deficiency are some of the diseases where the proposed mitochondrial network of Trx2 may be implicated.

Phosphoproteins Involved in the Inhibition of Apoptosis and in Cell Survival in the Leiomyoma

Uterine leiomyomas are benign smooth muscle cell tumors originating from the myometrium. In this study we focus on leiomyoma and normal myometrium phosphoproteome, to identify differentially phosphorylated proteins involved in tumorigenic signaling pathways, and in anti-apoptotic processes and cell survival. We obtained paired tissue samples of seven leiomyomas and adjacent myometria and analyzed the phosphoproteome by two-dimensional gel electrophoresis (2-DE) combined with immobilized metal affinity chromatography (IMAC) and Pro-Q Diamond phosphoprotein gel stain. We used mass spectrometry for protein identification and Western blotting for 2-DE data validation. Quantities of 33 proteins enriched by the IMAC approach were significantly different in the leiomyoma if compared to the myometrium. Bioinformatic analysis revealed ten tumorigenic signaling pathways and four phosphoproteins involved in both the inhibition of apoptosis and cell survival. Our study highlights the involvement of the phosphoproteome in leiomyoma growth. Further studies are needed to understand the role of phosphorylation in leiomyoma. Our data shed light on mechanisms that still need to be ascertained, but could open the path to a new class of drugs that not only can block the growth, but could also lead to a significant reduction in tumor size.

Hsp60 in Skeletal Muscle Fiber Biogenesis and Homeostasis: From Physical Exercise to Skeletal Muscle Pathology

Hsp60 is a molecular chaperone classically described as a mitochondrial protein with multiple roles in health and disease, participating to the maintenance of protein homeostasis. It is well known that skeletal muscle is a complex tissue, rich in proteins, that is, subjected to continuous rearrangements, and this homeostasis is affected by many different types of stimuli and stresses. The regular exercise induces specific histological and biochemical adaptations in skeletal muscle fibers, such as hypertrophy and an increase of mitochondria activity and oxidative capacity. The current literature is lacking in information regarding Hsp60 involvement in skeletal muscle fiber biogenesis and regeneration during exercise, and in disease conditions. Here, we briefly discuss the functions of Hsp60 in skeletal muscle fibers during exercise, inflammation, and ageing. Moreover, the potential usage of Hsp60 as a marker for disease and the evaluation of novel treatment options is also discussed. However, some questions remain open, and further studies are needed to better understand Hsp60 involvement in skeletal muscle homeostasis during exercise and in pathological condition.

Single-Ring Intermediates Are Essential for Some Chaperonins

Chaperonins are macromolecular complexes found throughout all kingdoms of life that assist unfolded proteins reach a biologically active state. Historically, chaperonins have been classified into two groups based on sequence, subunit structure, and the requirement for a co-chaperonin. Here, we present a brief review of chaperonins that can form double- and single-ring conformational intermediates in their protein-folding catalytic pathway. To date, the bacteriophage encoded chaperonins ϕ-EL and OBP, human mitochondrial chaperonin and most recently, the bacterial groEL/ES systems, have been reported to form single-ring intermediates as part of their normal protein-folding activity. These double-ring chaperonins separate into single-ring intermediates that have the ability to independently fold a protein. We discuss the structural and functional features along with the biological relevance of single-ring intermediates in cellular protein folding. Of special interest are the ϕ-EL and OBP chaperonins which demonstrate features of both group I and II chaperonins in addition to their ability to function via single-ring intermediates.

A Glimpse Into the Structure and Function of Atypical Type I Chaperonins

Chaperonins are a subclass of molecular chaperones that assist cellular proteins to fold and assemble into their native shape. Much work has been done on Type I chaperonins, which has elucidated their elegant mechanism. Some debate remains about the details in these mechanisms, but nonetheless the roles of these in helping protein folding have been understood in great depth. In this review we discuss the known functions of atypical Type I chaperonins, highlighting evolutionary aspects that might lead chaperonins to perform alternate functions.

Physicochemical Properties of the Mammalian Molecular Chaperone HSP60

The E. coli GroEL/GroES chaperonin complex acts as a folding cage by producing a bullet-like asymmetric complex, and GroEL exists as double rings regardless of the presence of adenosine triphosphate (ATP). Its mammalian chaperonin homolog, heat shock protein, HSP60, and co-chaperonin, HSP10, play an essential role in protein folding by capturing unfolded proteins in the HSP60/HSP10 complex. However, the structural transition in ATPase-dependent reaction cycle has remained unclear. We found nucleotide-dependent association and dissociation of the HSP60/HSP10 complex using various analytical techniques under near physiological conditions. Our results showed that HSP60 exist as a significant number of double-ring complexes (football- and bullet-type complexes) and a small number of single-ring complexes in the presence of ATP and HSP10. HSP10 binds to HSP60 in the presence of ATP, which increased the HSP60 double-ring formation. After ATP is hydrolyzed to Adenosine diphosphate (ADP), HSP60 released the HSP10 and the dissociation of the double-ring to single-rings occurred. These results indicated that HSP60/HSP10 undergoes an ATP-dependent transition between the single- and double-rings in their system that is highly distinctive from the GroEL/GroES system particularly in the manner of complex formation and the roles of ATP binding and hydrolysis in the reaction cycle.

Frataxin-deficient neurons and mice models of Friedreich ataxia are improved by TAT-MTScs-FXN treatment

Friedreich ataxia (FA) is a rare disease caused by deficiency of frataxin, a mitochondrial protein. As there is no cure available for this disease, many strategies have been developed to reduce the deleterious effects of such deficiency. One of these approaches is based on delivering frataxin to the tissues by coupling the protein to trans-activator of transcription (TAT) peptides, which enables cell membranes crossing. In this study, we tested the efficiency of TAT-MTScs-FXN fusion protein to decrease neurodegeneration markers on frataxin-depleted neurons obtained from dorsal root ganglia (DRG), one of the most affected tissues. In mice models of the disease, we tested the ability of TAT-MTScs-FXN to penetrate the mitochondria and its effect on lifespan. In DRG neurons, treatment with TAT-MTScs-FXN increased cell survival, decreased neurite degeneration and reduced apoptotic markers, such as α-fodrin cleavage and caspase 9 activation. Also, we show that heat-shock protein 60 (HSP60), a molecular chaperone targeted to mitochondria, suffered an impaired processing in frataxin-deficient neurons that was relieved by TAT-MTScs-FXN addition. In mice models of the disease, administration of TAT-MTScs-FXN was able to reach muscle mitochondria, restore the activity of the succinate dehydrogenase and produce a significant lifespan increase. These results support the use of TAT-MTScs-FXN as a treatment for Friedreich ataxia.

Chaperonin of Group I: Oligomeric Spectrum and Biochemical and Biological Implications

Chaperonins play various physiological roles and can also be pathogenic. Elucidation of their structure, e.g., oligomeric status and post-translational modifications (PTM), is necessary to understand their functions and mechanisms of action in health and disease. Group I chaperonins form tetradecamers with two stacked heptameric rings. The tetradecamer is considered the typical functional complex for folding of client polypeptides. However, other forms such as the monomer and oligomers with smaller number of subunits than the classical tetradecamer, also occur in cells. The properties and functions of the monomer and oligomers, and their roles in chaperonin-associated diseases are still incompletely understood. Chaperonin I in eukaryotes occurs in various locations, not just the mitochondrion, which is its canonical place of residence and function. Eukaryotic Chaperonin I, namely Hsp60 (designated HSP60 or HSPD1 in humans) has, indeed, been found in the cytosol; the plasma-cell membrane; on the outer surface of cells; in the intercellular space; in biological liquids such as lymph, blood, and cerebrospinal fluid; and in secretions, for instance saliva and urine. Hsp60 has also been found in cell-derived vesicles such as exosomes. The functions of Hsp60 in all these non-canonical locales are still poorly characterized and one of the questions not yet answered is in what form, i.e., monomer or oligomer, is the chaperonin present in these non-canonical locations. In view of the steady increase in interest on chaperonopathies over the last several years, we have studied human HSP60 to determine its role in various diseases, its locations in cells and tissues and migrations in the body, and its post-translational modifications that might have an impact on its location and function. We also carried out experiments to characterize the oligomeric status of extramitochondrial of HSP60 in solution. Here, we provide an overview of our results, focusing on the oligomeric equilibrium and stability of the various forms of HSP60 in comparison with GroEL. We also discuss post-translational modifications associated with anti-cancer drugs to indicate the potential of Hsp60 in Medicine, as a biomarker and etiopathogenic factor.

HSP60 possesses a GTPase activity and mediates protein folding with HSP10

The mammalian molecular chaperone, HSP60, plays an essential role in protein homeostasis through mediating protein folding and assembly. The structure and ATP-dependent function of HSP60 has been well established in recent studies. After ATP, GTP is the major cellular nucleotide. In this paper, we have investigated the role of GTP in the activity of HSP60. It was found that HSP60 has different properties with respect to allostery, complex formation and protein folding activity depending on the nucleoside triphosphate present. The presence of GTP slightly affected the ATPase activity of HSP60 during protein folding. These results provide clues as to the functional mechanism of the HSP60-HSP10 complex.

Creating the Functional Single-Ring GroEL-GroES Chaperonin Systems via Modulating GroEL-GroES Interaction

Chaperonin and cochaperonin, represented by E. coli GroEL and GroES, are essential molecular chaperones for protein folding. The double-ring assembly of GroEL is required to function with GroES, and a single-ring GroEL variant GroEL^SR forms a stable complex with GroES, arresting the chaperoning reaction cycle. GroES I25 interacts with GroEL; however, mutations of I25 abolish GroES-GroEL interaction due to the seven-fold mutational amplification in heptameric GroES. To weaken GroEL^SR-GroES interaction in a controlled manner, we used groES ⁷, a gene linking seven copies of groES, to incorporate I25 mutations in selected GroES modules in GroES⁷. We generated GroES⁷ variants with different numbers of GroESI25A or GroESI25D modules and different arrangements of the mutated modules, and biochemically characterized their interactions with GroEL^SR. GroES⁷ variants with two mutated modules participated in GroEL^SR-mediated protein folding in vitro. GroES⁷ variants with two or three mutated modules collaborated with GroEL^SR to perform chaperone function in vivo: three GroES⁷ variants functioned with GroEL^SR under both normal and heat-shock conditions. Our studies on functional single-ring bacterial chaperonin systems are informative to the single-ring human mitochondrial chaperonin mtHsp60-mtHsp10, and will provide insights into how the double-ring bacterial system has evolved to the single-ring mtHsp60-mtHsp10.

The human mitochondrial Hsp60 in the APO conformation forms a stable tetradecameric complex

The human mitochondrial chaperonin is a macromolecular machine that catalyzes the proper folding of mitochondrial proteins and is of vital importance to all cells. This chaperonin is composed of 2 distinct proteins, Hsp60 and Hsp10, that assemble into large oligomeric complexes that mediate the folding of non-native polypeptides in an ATP dependent manner. Here, we report the bacterial expression and purification of fully assembled human Hsp60 and Hsp10 recombinant proteins and that Hsp60 forms a stable tetradecameric double-ring conformation in the absence of co-chaperonin and nucleotide. Evidence of the stable double-ring conformation is illustrated by the 15 Å resolution electron microscopy reconstruction presented here. Furthermore, our biochemical analyses reveal that the presence of a non-native substrate initiates ATP-hydrolysis within the Hsp60/10 chaperonin to commence protein folding. Collectively, these data provide insight into the architecture of the intermediates used by the human mitochondrial chaperonin along its protein folding pathway and lay a foundation for subsequent high resolution structural investigations into the conformational changes of the mitochondrial chaperonin.

New GroEL-like chaperonin of bacteriophage OBP Pseudomonas fluorescens suppresses thermal protein aggregation in an ATP-dependent manner

Recently, we discovered and studied the first virus-encoded chaperonin of bacteriophage EL Pseudomonas aeruginosa, gene product (gp) 146. In the present study, we performed bioinformatics analysis of currently predicted GroEL-like proteins encoded by phage genomes in comparison with cellular and mitochondrial chaperonins. Putative phage chaperonins share a low similarity and do not form a monophyletic group; nevertheless, they are closer to bacterial chaperonins in the phylogenetic tree. Experimental investigation of putative GroEL-like chaperonin proteins has been continued by physicochemical and functional characterization of gp246 encoded by the genome of Pseudomonas fluorescens bacteriophage OBP. Unlike the more usual double-ring architecture of chaperonins, including the EL gp146, the recombinant gp246 produced by Escherichia coli cells has been purified as a single heptameric ring. It possesses ATPase activity and does not require a co-chaperonin for its function. In vitro experiments demonstrated that gp246 is able to suppress the thermal protein inactivation and aggregation in an ATP-dependent manner, thus indicating chaperonin function. Single-particle electron microscopy analysis revealed the different conformational states of OBP chaperonin, depending on the bound nucleotide.

Allosteric Mechanisms in Chaperonin Machines

Chaperonins are nanomachines that facilitate protein folding by undergoing energy (ATP)-dependent movements that are coordinated in time and space owing to complex allosteric regulation. They consist of two back-to-back stacked oligomeric rings with a cavity at each end where protein substrate folding can take place. Here, we focus on the GroEL/GroES chaperonin system from Escherichia coli and, to a lesser extent, on the more poorly characterized eukaryotic chaperonin CCT/TRiC. We describe their various functional (allosteric) states and how they are affected by substrates and allosteric effectors that include ATP, ADP, nonfolded protein substrates, potassium ions, and GroES (in the case of GroEL). We also discuss the pathways of intra- and inter-ring allosteric communication by which they interconvert and the coupling between allosteric transitions and protein folding reactions.

Functional structure and physiological functions of mammalian wild-type HSP60

The Chaperonins comprise a family of molecular chaperones having a double-ring structure and similar sequence homology. These proteins play an essential role in biological reactions that mediate the folding of newly synthesized polypeptides and partially denatured proteins. In the prokaryotic group I chaperonins, structural and reaction cycle analyses of GroEL and its co-chaperone GroES have been performed in detail. While in eukaryotes, there have been limited reports analyzing the group I chaperonin HSP60 and its co-chaperone HSP10. In the present study, we purified the wild type HSP60 from porcine liver and investigated the interaction between HSP60 and HSP10, including conformation and physiological relationships. Based on the results of transmission electron microscopy, native PAGE, and gel filtration column chromatography, the wild type HSP60 displayed a heptameric single-ring structure in the absence of ATP. In contrast, HSP60 formed mainly a "football-type" complex with HSP10 in the presence of ATP and mediated the refolding of denatured substrate protein. The functional conformation cycle of the purified mammalian HSP60 is distinct from the cycle of the prokaryotic GroEL/GroES chaperonin.

Crystal structure of the human mitochondrial chaperonin symmetrical football complex

Human mitochondria harbor a single type I chaperonin system that is generally thought to function via a unique single-ring intermediate. To date, no crystal structure has been published for any mammalian type I chaperonin complex. In this study, we describe the crystal structure of a football-shaped, double-ring human mitochondrial chaperonin complex at 3.15 Å, which is a novel intermediate, likely representing the complex in an early stage of dissociation. Interestingly, the mitochondrial chaperonin was captured in a state that exhibits subunit asymmetry within the rings and nucleotide symmetry between the rings. Moreover, the chaperonin tetradecamers show a different interring subunit arrangement when compared to GroEL. Our findings suggest that the mitochondrial chaperonins use a mechanism that is distinct from the mechanism of the well-studied Escherichia coli system.

Reaction Cycle of Chaperonin GroEL via Symmetric "Football" Intermediate

Chaperonin GroEL is an essential chaperone that assists in protein folding in the cell. Since one GroEL ring binds one GroES heptamer, the GroEL double ring permits the formation of two types of GroEL:GroES complexes: asymmetric 1:1 "bullet"-shaped and symmetric 1:2 "football"-shaped GroEL:GroES2 complexes. There have been continuing debates about the mechanism and which complex is critical to the chaperonin-assisted folding. In this review, I summarize the recent progress on the football complex.

Mitochondrial heat shock protein (Hsp) 70 and Hsp10 cooperate in the formation of Hsp60 complexes

Mitochondrial Hsp70 (mtHsp70) mediates essential functions for mitochondrial biogenesis, like import and folding of proteins. In these processes, the chaperone cooperates with cochaperones, the presequence translocase, and other chaperone systems. The chaperonin Hsp60, together with its cofactor Hsp10, catalyzes folding of a subset of mtHsp70 client proteins. Hsp60 forms heptameric ring structures that provide a cavity for protein folding. How the Hsp60 rings are assembled is poorly understood. In a comprehensive interaction study, we found that mtHsp70 associates with Hsp60 and Hsp10. Surprisingly, mtHsp70 interacts with Hsp10 independently of Hsp60. The mtHsp70-Hsp10 complex binds to the unassembled Hsp60 precursor to promote its assembly into mature Hsp60 complexes. We conclude that coupling to Hsp10 recruits mtHsp70 to mediate the biogenesis of the heptameric Hsp60 rings.

Crystal structure of a symmetric football-shaped GroEL:GroES2-ATP14 complex determined at 3.8Å reveals rearrangement between two GroEL rings

The chaperonin GroEL is an essential chaperone that assists in protein folding with the aid of GroES and ATP. GroEL forms a double-ring structure, and both rings can bind GroES in the presence of ATP. Recent progress on the GroEL mechanism has revealed the importance of a symmetric 1:2 GroEL:GroES2 complex (the "football"-shaped complex) as a critical intermediate during the functional GroEL cycle. We determined the crystal structure of the football GroEL:GroES2-ATP14 complex from Escherichia coli at 3.8Å, using a GroEL mutant that is extremely defective in ATP hydrolysis. The overall structure of the football complex resembled the GroES-bound GroEL ring of the asymmetric 1:1 GroEL:GroES complex (the "bullet" complex). However, the two GroES-bound GroEL rings form a modified interface by an ~7° rotation about the 7-fold axis. As a result, the inter-ring contacts between the two GroEL rings in the football complex differed from those in the bullet complex. The differences provide a structural basis for the apparently impaired inter-ring negative cooperativity observed in several biochemical analyses.

Human Hsp60 with its mitochondrial import signal occurs in solution as heptamers and tetradecamers remarkably stable over a wide range of concentrations

It has been established that Hsp60 can accumulate in the cytosol in various pathological conditions, including cancer and chronic inflammatory diseases. Part or all of the cytosolic Hsp60 could be naïve, namely, bear the mitochondrial import signal (MIS), but neither the structure nor the in solution oligomeric organization of this cytosolic molecule has still been elucidated. Here we present a detailed study of the structure and self-organization of naïve cytosolic Hsp60 in solution. Results were obtained by different biophysical methods (light and X ray scattering, single molecule spectroscopy and hydrodynamics) that all together allowed us to assay a wide range of concentrations of Hsp60. We found that Naïve Hsp60 in aqueous solution is assembled in very stable heptamers and tetradecamers at all concentrations assayed, without any trace of monomer presence.

IgG and IgA antibody titers against human heat-shock protein (hsp60) in sera of rheumatoid arthritis and osteoarthritis patients

Abstract To learn whether heat-shock proteins (HSP) are involved in the pathogenesis of rheumatoid arthritis (RA), antirecombinant human heat-shock protein 60 (hsp60) IgG and IgA in sera of RA and osteoarthritis (OA) patients were investigated. Only the anti-hsp60 IgG titer of seropositive (RF-positive) patients was found to be elevated. Although RF titers of the sera of seropositive RA patients were increased, there was no correlation between the individual anti-hsp60 IgG titer and the corresponding RF titer. In contrast, all the anti-hsp60 IgA titers of the sera of OA, seronegative RA, and seropositive RA patients were found to be elevated. Among them, only the serum IgA concentration of seropositive RA patients was increased. Thus, it was suggested that the increased anti-hsp60 IgG reflects the pathogenesis of RA and its activity. It was also suggested that the increased anti-hsp60 IgA response reflects an involvement of hsp60 in the pathogenesis of arthritides rather than the pathogenesis of RA.

P. falciparum cpn20 is a bona fide co-chaperonin that can replace GroES in E. coli

Human malaria is among the most ubiquitous and destructive tropical, parasitic diseases in the world today. The causative agent, Plasmodium falciparum, contains an unusual, essential organelle known as the apicoplast. Inhibition of this degenerate chloroplast results in second generation death of the parasite and is the mechanism by which antibiotics function in treating malaria. In order to better understand the biochemistry of this organelle, we have cloned a putative, 20 kDa, co-chaperonin protein, Pf-cpn20, which localizes to the apicoplast. Although this protein is homologous to the cpn20 that is found in plant chloroplasts, its ability to function as a co-chaperonin was questioned in the past. In the present study, we carried out a structural analysis of Pf-cpn20 using circular dichroism and analytical ultracentrifugation and then used two different approaches to investigate the ability of this protein to function as a co-chaperonin. In the first approach, we purified recombinant Pf-cpn20 and tested its ability to act as a co-chaperonin for GroEL in vitro, while in the second, we examined the ability of Pf-cpn20 to complement an E. coli depletion of the essential bacterial co-chaperonin GroES. Our results demonstrate that Pf-cpn20 is fully functional as a co-chaperonin in vitro. Moreover, the parasitic co-chaperonin is able to replace GroES in E. coli at both normal and heat-shock temperatures. Thus, Pf-cpn20 functions as a co-chaperonin in chaperonin-mediated protein folding. The ability of the malarial protein to function in E. coli suggests that this simple system can be used as a tool for further analyses of Pf-cpn20 and perhaps other chaperone proteins from P. falciparum.

Identification of elements that dictate the specificity of mitochondrial Hsp60 for its co-chaperonin

Type I chaperonins (cpn60/Hsp60) are essential proteins that mediate the folding of proteins in bacteria, chloroplast and mitochondria. Despite the high sequence homology among chaperonins, the mitochondrial chaperonin system has developed unique properties that distinguish it from the widely-studied bacterial system (GroEL and GroES). The most relevant difference to this study is that mitochondrial chaperonins are able to refold denatured proteins only with the assistance of the mitochondrial co-chaperonin. This is in contrast to the bacterial chaperonin, which is able to function with the help of co-chaperonin from any source. The goal of our work was to determine structural elements that govern the specificity between chaperonin and co-chaperonin pairs using mitochondrial Hsp60 as model system. We used a mutagenesis approach to obtain human mitochondrial Hsp60 mutants that are able to function with the bacterial co-chaperonin, GroES. We isolated two mutants, a single mutant (E321K) and a double mutant (R264K/E358K) that, together with GroES, were able to rescue an E. coli strain, in which the endogenous chaperonin system was silenced. Although the mutations are located in the apical domain of the chaperonin, where the interaction with co-chaperonin takes place, none of the residues are located in positions that are directly responsible for co-chaperonin binding. Moreover, while both mutants were able to function with GroES, they showed distinct functional and structural properties. Our results indicate that the phenotype of the E321K mutant is caused mainly by a profound increase in the binding affinity to all co-chaperonins, while the phenotype of R264K/E358K is caused by a slight increase in affinity toward co-chaperonins that is accompanied by an alteration in the allosteric signal transmitted upon nucleotide binding. The latter changes lead to a great increase in affinity for GroES, with only a minor increase in affinity toward the mammalian mitochondrial co-chaperonin.

Effects of chronic heat stress on the expressions of heat shock proteins 60, 70, 90, A2, and HSC70 in the rabbit testis

Few studies have focused on the expression of heat shock proteins (HSPs) after chronic heat stress. The objective of this study was to investigate the effect of chronic high temperature-humidity index treatment on the expressions of HSP60, HSP70, HSP90, HSPA2 and HSC70, in the Rex rabbit testis and the expressions of these proteins after recovery from the chronic heat shock. Thirty mature male rabbits of the same age were randomly divided into three groups: control, heat stress, and recovery. The western blot results showed that the expressional levels of HSP60, HSP90, and HSC70 increased significantly and HSPA2 was elevated slightly after a 9-week heat treatment. HSP70 was absent in the control testis and had a high level of expression after heat stress. All of these proteins partially reverted back to normal levels after a 9-week recovery. The immunohistochemical results indicated that the expression patterns of HSP60, HSP90, HSPA2, and HSC70 did not change.

Stimulating the substrate folding activity of a single ring GroEL variant by modulating the cochaperonin GroES

In mediating protein folding, chaperonin GroEL and cochaperonin GroES form an enclosed chamber for substrate proteins in an ATP-dependent manner. The essential role of the double ring assembly of GroEL is demonstrated by the functional deficiency of the single ring GroEL(SR). The GroEL(SR)-GroES is highly stable with minimal ATPase activity. To restore the ATP cycle and the turnover of the folding chamber, we sought to weaken the GroEL(SR)-GroES interaction systematically by concatenating seven copies of groES to generate groES(7). GroES Ile-25, Val-26, and Leu-27, residues on the GroEL-GroES interface, were substituted with Asp on different groES modules of groES(7). GroES(7) variants activate ATP activity of GroEL(SR), but only some restore the substrate folding function of GroEL(SR), indicating a direct role of GroES in facilitating substrate folding through its dynamics with GroEL. Active GroEL(SR)-GroES(7) systems may resemble mammalian mitochondrial chaperonin systems.

Characterisation of a GroEL single-ring mutant that supports growth of Escherichia coli and has GroES-dependent ATPase activity

Binding and folding of substrate proteins by the molecular chaperone GroEL alternates between its two seven-membered rings in an ATP-regulated manner. The association of ATP and GroES to a polypeptide-bound ring of GroEL encapsulates the folding proteins in the central cavity of that ring (cis ring) and allows it to fold in a protected environment where the risk of aggregation is reduced. ATP hydrolysis in the cis ring changes the potentials within the system such that ATP binding to the opposite (trans) ring triggers the release of all ligands from the cis ring of GroEL through a complex network of allosteric communication between the rings. Inter-ring allosteric communication thus appears indispensable for the function of GroEL, and an engineered single-ring version (SR1) cannot substitute for GroEL in vivo. We describe here the isolation and characterisation of an active single-ring form of the GroEL protein (SR-A92T), which has an exceptionally low ATPase activity that is strongly stimulated by the addition of GroES. Dissection of the kinetic pathway of the ATP-induced structural changes in this active single ring can be explained by the fact that the mutation effectively blocks progression through the full allosteric pathway of the GroEL reaction cycle, thus trapping an early allosteric intermediate. Addition of GroES is able to overcome this block by binding this intermediate and pulling the allosteric pathway to completion via mass action, explaining how bacterial cells expressing this protein as their only chaperonin are viable.

Increased light intensity induces heat shock protein Hsp60 in coral species

The effect of increased light intensity and heat stress on heat shock protein Hsp60 was examined in two coral species using a branched coral and a laminar coral, selected for their different resistance to environmental perturbation. Transient Hsp60 induction was observed in the laminar coral following either light or thermal stress. Sustained induction was observed when these stresses were combined. The branched coral exhibited comparatively weak transient Hsp60 induction after heat stress and no detectable induction following light stress, consistent with its susceptibility to bleaching in native environments compared to the laminar coral. Our observations also demonstrate that increased light intensity and heat stress exhibited a greater negative impact on the photosynthetic capacity of environmentally sensitive branched coral than the more resistant laminar coral. This supports a correlation between stress induction of Hsp60 and (a) ability to counter perturbation of photosynthetic capacity by light and heat stress and (b) resistance to environmentally induced coral bleaching.