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International Journal of Molecular... Dec 2022Besides protein processing, the endoplasmic reticulum (ER) has several other functions such as lipid synthesis, the transfer of molecules to other cellular compartments,... (Review)
Review
Besides protein processing, the endoplasmic reticulum (ER) has several other functions such as lipid synthesis, the transfer of molecules to other cellular compartments, and the regulation of Ca homeostasis. Before leaving the organelle, proteins must be folded and post-translationally modified. Protein folding and revision require molecular chaperones and a favorable ER environment. When in stressful situations, ER luminal conditions or chaperone capacity are altered, and the cell activates signaling cascades to restore a favorable folding environment triggering the so-called unfolded protein response (UPR) that can lead to autophagy to preserve cell integrity. However, when the UPR is disrupted or insufficient, cell death occurs. This review examines the links between UPR signaling, cell-protective responses, and death following ER stress with a particular focus on those mechanisms that operate in neurons.
Topics: Endoplasmic Reticulum Stress; Unfolded Protein Response; Endoplasmic Reticulum; Signal Transduction; Cell Death; Molecular Chaperones
PubMed: 36499512
DOI: 10.3390/ijms232315186 -
International Journal of Molecular... Sep 2021HSP90 is a vital chaperone protein conserved across all organisms. As a chaperone protein, it correctly folds client proteins. Structurally, this protein is a dimer with... (Review)
Review
HSP90 is a vital chaperone protein conserved across all organisms. As a chaperone protein, it correctly folds client proteins. Structurally, this protein is a dimer with monomer subunits that consist of three main conserved domains known as the N-terminal domain, middle domain, and the C-terminal domain. Multiple isoforms of HSP90 exist, and these isoforms share high homology. These isoforms are present both within the cell and outside the cell. Isoforms HSP90 and HSP90 are present in the cytoplasm; TRAP1 is present in the mitochondria; and GRP94 is present in the endoplasmic reticulum and is likely secreted due to post-translational modifications (PTM). HSP90 is also secreted into an extracellular environment via an exosome pathway that differs from the classic secretion pathway. Various co-chaperones are necessary for HSP90 to function. Elevated levels of HSP90 have been observed in patients with cancer. Despite this observation, the possible role of HSP90 in cancer was overlooked because the chaperone was also present in extreme amounts in normal cells and was vital to normal cell function, as observed when the drastic adverse effects resulting from gene knockout inhibited the production of this protein. Differences between normal HSP90 and HSP90 of the tumor phenotype have been better understood and have aided in making the chaperone protein a target for cancer drugs. One difference is in the conformation: HSP90 of the tumor phenotype is more susceptible to inhibitors. Since overexpression of HSP90 is a factor in tumorigenesis, HSP90 inhibitors have been studied to combat the adverse effects of HSP90 overexpression. Monotherapies using HSP90 inhibitors have shown some success; however, combination therapies have shown better results and are thus being studied for a more effective cancer treatment.
Topics: Animals; Carcinogenesis; HSP90 Heat-Shock Proteins; Humans; Molecular Chaperones; Neoplasms; Protein Isoforms
PubMed: 34638658
DOI: 10.3390/ijms221910317 -
Nature Jan 2022Hsp90 is a conserved and essential molecular chaperone responsible for the folding and activation of hundreds of 'client' proteins. The glucocorticoid receptor (GR) is a...
Hsp90 is a conserved and essential molecular chaperone responsible for the folding and activation of hundreds of 'client' proteins. The glucocorticoid receptor (GR) is a model client that constantly depends on Hsp90 for activity. GR ligand binding was previously shown to nr inhibited by Hsp70 and restored by Hsp90, aided by the co-chaperone p23. However, a molecular understanding of the chaperone-mediated remodelling that occurs between the inactive Hsp70-Hsp90 'client-loading complex' and an activated Hsp90-p23 'client-maturation complex' is lacking for any client, including GR. Here we present a cryo-electron microscopy (cryo-EM) structure of the human GR-maturation complex (GR-Hsp90-p23), revealing that the GR ligand-binding domain is restored to a folded, ligand-bound conformation, while being simultaneously threaded through the Hsp90 lumen. In addition, p23 directly stabilizes native GR using a C-terminal helix, resulting in enhanced ligand binding. This structure of a client bound to Hsp90 in a native conformation contrasts sharply with the unfolded kinase-Hsp90 structure. Thus, aided by direct co-chaperone-client interactions, Hsp90 can directly dictate client-specific folding outcomes. Together with the GR-loading complex structure, we present the molecular mechanism of chaperone-mediated GR remodelling, establishing the first, to our knowledge, complete chaperone cycle for any Hsp90 client.
Topics: Cryoelectron Microscopy; HSP70 Heat-Shock Proteins; HSP90 Heat-Shock Proteins; Humans; Ligands; Molecular Chaperones; Prostaglandin-E Synthases; Protein Binding; Receptors, Glucocorticoid
PubMed: 34937936
DOI: 10.1038/s41586-021-04236-1 -
Nature Jan 2022Maintaining a healthy proteome is fundamental for the survival of all organisms. Integral to this are Hsp90 and Hsp70, molecular chaperones that together facilitate the...
Maintaining a healthy proteome is fundamental for the survival of all organisms. Integral to this are Hsp90 and Hsp70, molecular chaperones that together facilitate the folding, remodelling and maturation of the many 'client proteins' of Hsp90. The glucocorticoid receptor (GR) is a model client protein that is strictly dependent on Hsp90 and Hsp70 for activity. Chaperoning GR involves a cycle of inactivation by Hsp70; formation of an inactive GR-Hsp90-Hsp70-Hop 'loading' complex; conversion to an active GR-Hsp90-p23 'maturation' complex; and subsequent GR release. However, to our knowledge, a molecular understanding of this intricate chaperone cycle is lacking for any client protein. Here we report the cryo-electron microscopy structure of the GR-loading complex, in which Hsp70 loads GR onto Hsp90, uncovering the molecular basis of direct coordination by Hsp90 and Hsp70. The structure reveals two Hsp70 proteins, one of which delivers GR and the other scaffolds the Hop cochaperone. Hop interacts with all components of the complex, including GR, and poises Hsp90 for subsequent ATP hydrolysis. GR is partially unfolded and recognized through an extended binding pocket composed of Hsp90, Hsp70 and Hop, revealing the mechanism of GR loading and inactivation. Together with the GR-maturation complex structure, we present a complete molecular mechanism of chaperone-dependent client remodelling, and establish general principles of client recognition, inhibition, transfer and activation.
Topics: Cryoelectron Microscopy; HSP70 Heat-Shock Proteins; HSP90 Heat-Shock Proteins; Homeodomain Proteins; Humans; Molecular Chaperones; Protein Binding; Protein Folding; Receptors, Glucocorticoid
PubMed: 34937942
DOI: 10.1038/s41586-021-04252-1 -
Cell Death & Disease Nov 2022Heat shock protein (HSP) 90, an important component of the molecular chaperone network, is closely concerned with cellular signaling pathways and stress response by... (Review)
Review
Heat shock protein (HSP) 90, an important component of the molecular chaperone network, is closely concerned with cellular signaling pathways and stress response by participating in the process of maturation and activation of client proteins, playing a crucial role both in the normal and abnormal operation of the organism. In functionally defective tissues, programmed cell death (PCD) is one of the regulable fundamental mechanisms mediated by HSP90, including apoptosis, autophagy, necroptosis, ferroptosis, and others. Here, we show the complex relationship between HSP90 and different types of PCD in various diseases, and discuss the possibility of HSP90 as the common regulatory nodal in multiple PCD, which would provide a new perspective for the therapeutic approaches in disease.
Topics: Humans; HSP90 Heat-Shock Proteins; Apoptosis; Molecular Chaperones; Autophagy
PubMed: 36335088
DOI: 10.1038/s41419-022-05373-9 -
Molecular Cell May 2023Because of the central role ribosomes play for protein translation and ribosome-mediated mRNA and protein quality control (RQC), the ribosome pool is surveyed and...
Because of the central role ribosomes play for protein translation and ribosome-mediated mRNA and protein quality control (RQC), the ribosome pool is surveyed and dysfunctional ribosomes degraded both during assembly, as well as the functional cycle. Oxidative stress downregulates translation and damages mRNAs and ribosomal proteins (RPs). Although damaged mRNAs are detected and degraded via RQC, how cells mitigate damage to RPs is not known. Here, we show that cysteines in Rps26 and Rpl10 are readily oxidized, rendering the proteins non-functional. Oxidized Rps26 and Rpl10 are released from ribosomes by their chaperones, Tsr2 and Sqt1, and the damaged ribosomes are subsequently repaired with newly made proteins. Ablation of this pathway impairs growth, which is exacerbated under oxidative stress. These findings reveal an unanticipated mechanism for chaperone-mediated ribosome repair, augment our understanding of ribosome quality control, and explain previous observations of protein exchange in ribosomes from dendrites, with broad implications for aging and health.
Topics: Ribosomes; Ribosomal Proteins; Molecular Chaperones; Oxidative Stress; Protein Biosynthesis
PubMed: 37086725
DOI: 10.1016/j.molcel.2023.03.030 -
The Hsp90 molecular chaperone governs client proteins by targeting intrinsically disordered regions.Molecular Cell Jun 2023Molecular chaperones govern proteome health to support cell homeostasis. An essential eukaryotic component of the chaperone system is Hsp90. Using a chemical-biology...
Molecular chaperones govern proteome health to support cell homeostasis. An essential eukaryotic component of the chaperone system is Hsp90. Using a chemical-biology approach, we characterized the features driving the Hsp90 physical interactome. We found that Hsp90 associated with ∼20% of the yeast proteome using its three domains to preferentially target intrinsically disordered regions (IDRs) of client proteins. Hsp90 selectively utilized an IDR to regulate client activity as well as maintained IDR-protein health by preventing the transition to stress granules or P-bodies at physiological temperatures. We also discovered that Hsp90 controls the fidelity of ribosome initiation that triggers a heat shock response when disrupted. Our study provides insights into how this abundant molecular chaperone supports a dynamic and healthy native protein landscape.
Topics: Humans; HSP90 Heat-Shock Proteins; Molecular Chaperones; Proteome; Saccharomyces cerevisiae; Intrinsically Disordered Proteins
PubMed: 37295430
DOI: 10.1016/j.molcel.2023.05.021 -
Molecular Cell Apr 2023A multitude of histone chaperones are required to support histones from their biosynthesis until DNA deposition. They cooperate through the formation of histone...
A multitude of histone chaperones are required to support histones from their biosynthesis until DNA deposition. They cooperate through the formation of histone co-chaperone complexes, but the crosstalk between nucleosome assembly pathways remains enigmatic. Using exploratory interactomics, we define the interplay between human histone H3-H4 chaperones in the histone chaperone network. We identify previously uncharacterized histone-dependent complexes and predict the structure of the ASF1 and SPT2 co-chaperone complex, expanding the role of ASF1 in histone dynamics. We show that DAXX provides a unique functionality to the histone chaperone network, recruiting histone methyltransferases to promote H3K9me3 catalysis on new histone H3.3-H4 prior to deposition onto DNA. Hereby, DAXX provides a molecular mechanism for de novo H3K9me3 deposition and heterochromatin assembly. Collectively, our findings provide a framework for understanding how cells orchestrate histone supply and employ targeted deposition of modified histones to underpin specialized chromatin states.
Topics: Humans; Histones; Histone Chaperones; Nucleosomes; Cell Cycle Proteins; DNA; Molecular Chaperones; Co-Repressor Proteins
PubMed: 36868228
DOI: 10.1016/j.molcel.2023.02.009 -
Cells Jan 2023Calnexin is a type I integral endoplasmic reticulum (ER) membrane protein with an N-terminal domain that resides in the lumen of the ER and a C-terminal domain that... (Review)
Review
Calnexin is a type I integral endoplasmic reticulum (ER) membrane protein with an N-terminal domain that resides in the lumen of the ER and a C-terminal domain that extends into the cytosol. Calnexin is commonly referred to as a molecular chaperone involved in the folding and quality control of membrane-associated and secreted proteins, a function that is attributed to its ER- localized domain with a structure that bears a strong resemblance to another luminal ER chaperone and Ca-binding protein known as calreticulin. Studies have discovered that the cytosolic C-terminal domain of calnexin undergoes distinct post-translational modifications and interacts with a variety of proteins. Here, we discuss recent findings and hypothesize that the post-translational modifications of the calnexin C-terminal domain and its interaction with specific cytosolic proteins play a role in coordinating ER functions with events taking place in the cytosol and other cellular compartments.
Topics: Calnexin; Molecular Chaperones; Endoplasmic Reticulum; Membrane Proteins; Cytosol
PubMed: 36766745
DOI: 10.3390/cells12030403 -
Biomolecules Jan 2023Heat shock protein 90 (Hsp90) is a highly conserved molecular chaperone that assists in the maturation of many client proteins involved in cellular signal transduction.... (Review)
Review
Heat shock protein 90 (Hsp90) is a highly conserved molecular chaperone that assists in the maturation of many client proteins involved in cellular signal transduction. As a regulator of cellular signaling processes, it is vital for the maintenance of cellular proteostasis and adaptation to environmental stresses. Emerging research shows that Hsp90 function in an organism goes well beyond intracellular proteostasis. In metazoans, Hsp90, as an environmentally responsive chaperone, is involved in inter-tissue stress signaling responses that coordinate and safeguard cell nonautonomous proteostasis and organismal health. In this way, Hsp90 has the capacity to influence evolution and aging, and effect behavioral responses to facilitate tissue-defense systems that ensure organismal survival. In this review, I summarize the literature on the organismal roles of Hsp90 uncovered in multicellular organisms, from plants to invertebrates and mammals.
Topics: Humans; Animals; HSP90 Heat-Shock Proteins; Molecular Chaperones; Signal Transduction; Proteostasis; Stress, Physiological; Mammals
PubMed: 36830620
DOI: 10.3390/biom13020251