-
Cold Spring Harbor Perspectives in... Sep 2019Heat shock protein 90 (Hsp90) is a molecular chaperone involved in the maturation of a plethora of substrates ("clients"), including protein kinases, transcription... (Review)
Review
Heat shock protein 90 (Hsp90) is a molecular chaperone involved in the maturation of a plethora of substrates ("clients"), including protein kinases, transcription factors, and E3 ubiquitin ligases, positioning Hsp90 as a central regulator of cellular proteostasis. Hsp90 undergoes large conformational changes during its ATPase cycle. The processing of clients by cytosolic Hsp90 is assisted by a cohort of cochaperones that affect client recruitment, Hsp90 ATPase function or conformational rearrangements in Hsp90. Because of the importance of Hsp90 in regulating central cellular pathways, strategies for the pharmacological inhibition of the Hsp90 machinery in diseases such as cancer and neurodegeneration are being developed. In this review, we summarize recent structural and mechanistic progress in defining the function of organelle-specific and cytosolic Hsp90, including the impact of individual cochaperones on the maturation of specific clients and complexes with clients as well as ways of exploiting Hsp90 as a drug target.
Topics: Adenosine Triphosphatases; Animals; Binding Sites; Cytosol; Databases, Protein; Evolution, Molecular; Gene Expression Regulation; HSP90 Heat-Shock Proteins; Humans; Membrane Glycoproteins; Mental Disorders; Mice; Mitochondria; Molecular Chaperones; Neurodegenerative Diseases; Peptides; Protein Domains; Protein Isoforms; Proteostasis
PubMed: 30745292
DOI: 10.1101/cshperspect.a034017 -
Cell Mar 2023Hsp60 chaperonins and their Hsp10 cofactors assist protein folding in all living cells, constituting the paradigmatic example of molecular chaperones. Despite extensive...
Hsp60 chaperonins and their Hsp10 cofactors assist protein folding in all living cells, constituting the paradigmatic example of molecular chaperones. Despite extensive investigations of their structure and mechanism, crucial questions regarding how these chaperonins promote folding remain unsolved. Here, we report that the bacterial Hsp60 chaperonin GroEL forms a stable, functionally relevant complex with the chaperedoxin CnoX, a protein combining a chaperone and a redox function. Binding of GroES (Hsp10 cofactor) to GroEL induces CnoX release. Cryoelectron microscopy provided crucial structural information on the GroEL-CnoX complex, showing that CnoX binds GroEL outside the substrate-binding site via a highly conserved C-terminal α-helix. Furthermore, we identified complexes in which CnoX, bound to GroEL, forms mixed disulfides with GroEL substrates, indicating that CnoX likely functions as a redox quality-control plugin for GroEL. Proteins sharing structural features with CnoX exist in eukaryotes, suggesting that Hsp60 molecular plugins have been conserved through evolution.
Topics: Cryoelectron Microscopy; Protein Folding; Molecular Chaperones; Oxidation-Reduction; Chaperonins; Chaperonin 60; Chaperonin 10
PubMed: 36764293
DOI: 10.1016/j.cell.2023.01.013 -
Trends in Cell Biology Jan 2023The J-domain proteins (JDP) form the largest protein family among cellular chaperones. In cooperation with the Hsp70 chaperone system, these co-chaperones orchestrate a... (Review)
Review
The J-domain proteins (JDP) form the largest protein family among cellular chaperones. In cooperation with the Hsp70 chaperone system, these co-chaperones orchestrate a plethora of distinct functions, including those that help maintain cellular proteostasis and development. JDPs evolved largely through the fusion of a J-domain with other protein subdomains. The highly conserved J-domain facilitates the binding and activation of Hsp70s. How JDPs (re)wire Hsp70 chaperone circuits and promote functional diversity remains insufficiently explained. Here, we discuss recent advances in our understanding of the JDP family with a focus on the regulation built around J-domains to ensure correct pairing and assembly of JDP-Hsp70 machineries that operate on different clientele under various cellular growth conditions.
Topics: Humans; HSP40 Heat-Shock Proteins; Proteostasis; Molecular Chaperones; HSP70 Heat-Shock Proteins; Protein Binding
PubMed: 35729039
DOI: 10.1016/j.tcb.2022.05.004 -
Protein Science : a Publication of the... Aug 2022Molecular chaperones are essential to maintain proteostasis. While the functions of intracellular molecular chaperones that oversee protein synthesis, folding and...
Molecular chaperones are essential to maintain proteostasis. While the functions of intracellular molecular chaperones that oversee protein synthesis, folding and aggregation, are established, those specialized to work in the extracellular environment are less understood. Extracellular proteins reside in a considerably more oxidizing milieu than cytoplasmic proteins and are stabilized by abundant disulfide bonds. Hence, extracellular proteins are potentially destabilized and sensitive to aggregation under reducing conditions. We combine biochemical and mass spectrometry experiments and elucidate that the molecular chaperone functions of the extracellular protein domain Bri2 BRICHOS only appear under reducing conditions, through the assembly of monomers into large polydisperse oligomers by an intra- to intermolecular disulfide bond relay mechanism. Chaperone-active assemblies of the Bri2 BRICHOS domain are efficiently generated by physiological thiol-containing compounds and proteins, and appear in parallel with reduction-induced aggregation of extracellular proteins. Our results give insights into how potent chaperone activity can be generated from inactive precursors under conditions that are destabilizing to most extracellular proteins and thereby support protein stability/folding in the extracellular space. SIGNIFICANCE: Chaperones are essential to cells as they counteract toxic consequences of protein misfolding particularly under stress conditions. Our work describes a novel activation mechanism of an extracellular molecular chaperone domain, called Bri2 BRICHOS. This mechanism is based on reducing conditions that initiate small subunits to assemble into large oligomers via a disulfide relay mechanism. Activated Bri2 BRICHOS inhibits reduction-induced aggregation of extracellular proteins and could be a means to boost proteostasis in the extracellular environment upon reductive stress.
Topics: Adenosine Triphosphate; Disulfides; Molecular Chaperones; Protein Domains; Protein Folding
PubMed: 35900025
DOI: 10.1002/pro.4378 -
Cell Stress & Chaperones Jul 2020Imbalances of cellular proteostasis are linked to ageing and human diseases, including neurodegenerative and neuromuscular diseases. Heat shock proteins (HSPs) and small... (Review)
Review
Imbalances of cellular proteostasis are linked to ageing and human diseases, including neurodegenerative and neuromuscular diseases. Heat shock proteins (HSPs) and small heat shock proteins (sHSPs) together form a crucial core of the molecular chaperone family that plays a vital role in maintaining cellular proteostasis by shielding client proteins against aggregation and misfolding. sHSPs are thought to act as the first line of defence against protein unfolding/misfolding and have been suggested to act as "sponges" that rapidly sequester these aberrant species for further processing, refolding, or degradation, with the assistance of the HSP70 chaperone system. Understanding how these chaperones work at the molecular level will offer unprecedented insights for their manipulation as therapeutic avenues for the treatment of ageing and human disease. The evolution in single-molecule force spectroscopy techniques, such as optical tweezers (OT) and atomic force microscopy (AFM), over the last few decades have made it possible to explore at the single-molecule level the structural dynamics of HSPs and sHSPs and to examine the key molecular mechanisms underlying their chaperone activities. In this paper, we describe the working principles of OT and AFM and the experimental strategies used to employ these techniques to study molecular chaperones. We then describe the results of some of the most relevant single-molecule manipulation studies on HSPs and sHSPs and discuss how these findings suggest a more complex physiological role for these chaperones than previously assumed.
Topics: Animals; Bacteria; Heat-Shock Proteins, Small; Humans; Microscopy, Atomic Force; Optical Tweezers; Plants; Protein Folding; Proteostasis; Stress, Mechanical
PubMed: 32253740
DOI: 10.1007/s12192-020-01096-y -
Biomolecules Apr 2022Hsp90 (Heat Shock Protein 90) is an ATP (Adenosine triphosphate) molecular chaperone responsible for the activation and maturation of client proteins. The mechanism by... (Review)
Review
Hsp90 (Heat Shock Protein 90) is an ATP (Adenosine triphosphate) molecular chaperone responsible for the activation and maturation of client proteins. The mechanism by which Hsp90 achieves such activation, involving structurally diverse client proteins, has remained enigmatic. However, recent advances using structural techniques, together with advances in biochemical studies, have not only defined the chaperone cycle but have shed light on its mechanism of action. Hsp90 hydrolysis of ATP by each protomer may not be simultaneous and may be dependent on the specific client protein and co-chaperone complex involved. Surprisingly, Hsp90 appears to remodel client proteins, acting as a means by which the structure of the client protein is modified to allow its subsequent refolding to an active state, in the case of kinases, or by making the client protein competent for hormone binding, as in the case of the GR (glucocorticoid receptor). This review looks at selected examples of client proteins, such as CDK4 (cyclin-dependent kinase 4) and GR, which are activated according to the so-called 'remodelling hypothesis' for their activation. A detailed description of these activation mechanisms is paramount to understanding how Hsp90-associated diseases develop.
Topics: Adenosine Triphosphate; HSP90 Heat-Shock Proteins; Humans; Molecular Chaperones; Receptors, Glucocorticoid
PubMed: 35625528
DOI: 10.3390/biom12050600 -
Biomolecules Aug 2022The highly conserved molecular chaperone heat shock protein 90 (Hsp90) is well-known for maintaining metastable proteins and mediating various aspects of intracellular... (Review)
Review
The highly conserved molecular chaperone heat shock protein 90 (Hsp90) is well-known for maintaining metastable proteins and mediating various aspects of intracellular protein dynamics. Intriguingly, high-throughput interactome studies suggest that Hsp90 is associated with a variety of other pathways. Here, we will highlight the potential impact of Hsp90 in protein transport. Currently, a limited number of studies have defined a few mechanistic contributions of Hsp90 to protein transport, yet the relevance of hundreds of additional connections between Hsp90 and factors known to aide this process remains unresolved. These interactors broadly support transport pathways including endocytic and exocytic vesicular transport, the transfer of polypeptides across membranes, or unconventional protein secretion. In resolving how Hsp90 contributes to the protein transport process, new therapeutic targets will likely be obtained for the treatment of numerous human health issues, including bacterial infection, cancer metastasis, and neurodegeneration.
Topics: Cytosol; HSP90 Heat-Shock Proteins; Humans; Molecular Chaperones; Protein Transport
PubMed: 36008972
DOI: 10.3390/biom12081077 -
International Journal of Molecular... Oct 2019Proper folding is crucial for proteins to achieve functional activity in the cell. However, it often occurs that proteins are improperly folded (misfolded) and form... (Review)
Review
Proper folding is crucial for proteins to achieve functional activity in the cell. However, it often occurs that proteins are improperly folded (misfolded) and form aggregates, which are the main hallmark of many diseases including cancers, neurodegenerative diseases and many others. Proteins that assist other proteins in proper folding into three-dimensional structures are chaperones and co-chaperones. The key role of chaperones/co-chaperones is to prevent protein aggregation, especially under stress. An imbalance between chaperone/co-chaperone levels has been documented in neurons, and suggested to contribute to protein misfolding. An essential protein and a major regulator of protein folding in all eukaryotic cells is the heat shock protein 90 (Hsp90). The function of Hsp90 is tightly regulated by many factors, including co-chaperones. In this review we summarize results regarding the role of Hsp90 and its co-chaperones in neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and prionopathies.
Topics: Animals; Biomarkers; Disease Susceptibility; Gene Expression Regulation; HSP90 Heat-Shock Proteins; Humans; Molecular Chaperones; Neurodegenerative Diseases; Signal Transduction
PubMed: 31600883
DOI: 10.3390/ijms20204976 -
The EMBO Journal Dec 2023Protein requirements of eukaryotic cells are ensured by proteostasis, which is mediated by tight control of TORC1 activity. Upon TORC1 inhibition, protein degradation is...
Protein requirements of eukaryotic cells are ensured by proteostasis, which is mediated by tight control of TORC1 activity. Upon TORC1 inhibition, protein degradation is increased and protein synthesis is reduced through inhibition of translation initiation to maintain cell viability. Here, we show that the ribosome-associated complex (RAC)/Ssb chaperone system, composed of the HSP70 chaperone Ssb and its HSP40 co-chaperone Zuo1, is required to maintain proteostasis and cell viability under TORC1 inhibition in Saccharomyces cerevisiae. In the absence of Zuo1, translation does not decrease in response to the loss of TORC1 activity. A functional interaction between Zuo1 and Ssb is required for proper translational control and proteostasis maintenance upon TORC1 inhibition. Furthermore, we have shown that the rapid degradation of eIF4G following TORC1 inhibition is mediated by autophagy and is prevented in zuo1Δ cells, contributing to decreased survival in these conditions. We found that autophagy is defective in zuo1Δ cells, which impedes eIF4G degradation upon TORC1 inhibition. Our findings identify an essential role for RAC/Ssb in regulating translation in response to changes in TORC1 signalling.
Topics: Eukaryotic Initiation Factor-4G; HSP70 Heat-Shock Proteins; Molecular Chaperones; Ribosomes; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins
PubMed: 37984430
DOI: 10.15252/embj.2022113240 -
Journal of Molecular Biology Oct 2021Stunning advances have been achieved in addressing the protein folding problem, providing deeper understanding of the mechanisms by which proteins navigate energy... (Review)
Review
Stunning advances have been achieved in addressing the protein folding problem, providing deeper understanding of the mechanisms by which proteins navigate energy landscapes to reach their native states and enabling powerful algorithms to connect sequence to structure. However, the realities of the in vivo protein folding problem remain a challenge to reckon with. Here, we discuss the concept of the "proteome folding problem"-the problem of how organisms build and maintain a functional proteome-by admitting that folding energy landscapes are characterized by many misfolded states and that cells must deploy a network of chaperones and degradation enzymes to minimize deleterious impacts of these off-pathway species. The resulting proteostasis network is an inextricable part of in vivo protein folding and must be understood in detail if we are to solve the proteome folding problem. We discuss how the development of computational models for the proteostasis network's actions and the relationship to the biophysical properties of the proteome has begun to offer new insights and capabilities.
Topics: Animals; Humans; Molecular Chaperones; Protein Folding; Proteome; Proteostasis
PubMed: 34391802
DOI: 10.1016/j.jmb.2021.167197