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McFarland R, Reichow S. Dynamic fibrillar assembly of αB-crystallin induced by perturbation of the conserved NT-IXI motif resolved by cryo-EM. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.03.22.586355. [PMID: 38585788 PMCID: PMC10996541 DOI: 10.1101/2024.03.22.586355] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/09/2024]
Abstract
αB-crystallin is an archetypical member of the small heat-shock proteins (sHSPs) vital for cellular proteostasis and mitigating protein misfolding diseases. Gaining insights into the principles defining their molecular organization and chaperone function have been hindered by intrinsic dynamic properties and limited high-resolution structural analysis. To disentangle the mechanistic underpinnings of these dynamical properties, we mutated a conserved IXI-motif located within the N-terminal (NT) domain of human αB-crystallin. This resulted in a profound structural transformation, from highly polydispersed caged-like native assemblies into a comparatively well-ordered helical fibril state amenable to high-resolution cryo-EM analysis. The reversible nature of the induced fibrils facilitated interrogation of functional effects due to perturbation of the NT-IXI motif in both the native-like oligomer and fibril states. Together, our investigations unveiled several features thought to be key mechanistic attributes to sHSPs and point to a critical significance of the NT-IXI motif in αB-crystallin assembly, dynamics and chaperone activity.
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Affiliation(s)
- Russell McFarland
- Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, Portland, Oregon 97239, USA
- Vollum Institute, Oregon Health & Science University, Portland, Oregon 97239, USA
- Department of Chemistry, Portland State University, Portland, Oregon 97201, USA
- Current: Department of Biochemistry & Molecular Genetics, University of Colorado School of Medicine, Aurora, Colorado 80045
| | - Steve Reichow
- Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, Portland, Oregon 97239, USA
- Vollum Institute, Oregon Health & Science University, Portland, Oregon 97239, USA
- Department of Chemistry, Portland State University, Portland, Oregon 97201, USA
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2
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Lee J, Ryu B, Kim T, Kim KK. Cryo-EM structure of a 16.5-kDa small heat-shock protein from Methanocaldococcus jannaschii. Int J Biol Macromol 2024; 258:128763. [PMID: 38103675 DOI: 10.1016/j.ijbiomac.2023.128763] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2023] [Revised: 12/07/2023] [Accepted: 12/11/2023] [Indexed: 12/19/2023]
Abstract
The small heat-shock protein (sHSP) from the archaea Methanocaldococcus jannaschii, MjsHSP16.5, functions as a broad substrate ATP-independent holding chaperone protecting misfolded proteins from aggregation under stress conditions. This protein is the first sHSP characterized by X-ray crystallography, thereby contributing significantly to our understanding of sHSPs. However, despite numerous studies assessing its functions and structures, the precise arrangement of the N-terminal domains (NTDs) within this sHSP cage remains elusive. Here we present the cryo-electron microscopy (cryo-EM) structure of MjsHSP16.5 at 2.49-Å resolution. The subunits of MjsHSP16.5 in the cryo-EM structure exhibit lesser compaction compared to their counterparts in the crystal structure. This structural feature holds particular significance in relation to the biophysical properties of MjsHSP16.5, suggesting a close resemblance to this sHSP native state. Additionally, our cryo-EM structure unveils the density of residues 24-33 within the NTD of MjsHSP16.5, a feature that typically remains invisible in the majority of its crystal structures. Notably, these residues show a propensity to adopt a β-strand conformation and engage in antiparallel interactions with strand β1, both intra- and inter-subunit modes. These structural insights are corroborated by structural predictions, disulfide bond cross-linking studies of Cys-substitution mutants, and protein disaggregation assays. A comprehensive understanding of the structural features of MjsHSP16.5 expectedly holds the potential to inspire a wide range of interdisciplinary applications, owing to the renowned versatility of this sHSP as a nanoscale protein platform.
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Affiliation(s)
- Joohyun Lee
- Department of Precision Medicine, Graduate School of Basic Medical Science (GSBMS), Institute for Antimicrobial Resistance Research and Therapeutics, Sungkyunkwan University School of Medicine, Suwon 16419, Republic of Korea
| | - Bumhan Ryu
- Research Solution Center, Institute for Basic Science (IBS), Daejeon 34126, Republic of Korea
| | - Truc Kim
- Department of Precision Medicine, Graduate School of Basic Medical Science (GSBMS), Institute for Antimicrobial Resistance Research and Therapeutics, Sungkyunkwan University School of Medicine, Suwon 16419, Republic of Korea.
| | - Kyeong Kyu Kim
- Department of Precision Medicine, Graduate School of Basic Medical Science (GSBMS), Institute for Antimicrobial Resistance Research and Therapeutics, Sungkyunkwan University School of Medicine, Suwon 16419, Republic of Korea.
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Wang C, Teng L, Liu ZS, Kamalova A, McMenimen KA. HspB5 Chaperone Structure and Activity Are Modulated by Chemical-Scale Interactions in the ACD Dimer Interface. Int J Mol Sci 2023; 25:471. [PMID: 38203641 PMCID: PMC10778692 DOI: 10.3390/ijms25010471] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2023] [Revised: 12/24/2023] [Accepted: 12/27/2023] [Indexed: 01/12/2024] Open
Abstract
Small heat shock proteins (sHsps) are a family of ATP-independent molecular chaperones that function as "holdases" and prevent protein aggregation due to changes in temperature, pH, or oxidation state. sHsps have a conserved α-crystallin domain (ACD), which forms the dimer building block, flanked by variable N- and C-terminal regions. sHsps populate various oligomeric states as a function of their sequestrase activity, and these dynamic structural features allow the proteins to interact with a plethora of cellular substrates. However, the molecular mechanisms of their dynamic conformational assembly and the interactions with various substrates remains unclear. Therefore, it is important to gain insight into the underlying physicochemical properties that influence sHsp structure in an effort to understand their mechanism(s) of action. We evaluated several disease-relevant mutations, D109A, F113Y, R116C, R120G, and R120C, in the ACD of HspB5 for changes to in vitro chaperone activity relative to that of wildtype. Structural characteristics were also evaluated by ANS fluorescence and CD spectroscopy. Our results indicated that mutation Y113F is an efficient holdase, while D109A and R120G, which are found in patients with myofibrillar myopathy and cataracts, respectively, exhibit a large reduction in holdase activity in a chaperone-like light-scattering assay, which indicated alterations in substrate-sHsp interactions. The extent of the reductions in chaperone activities are different among the mutants and specific to the substrate protein, suggesting that while sHsps are able to interact with many substrates, specific interactions provide selectivity for some substrates compared to others. This work is consistent with a model for chaperone activity where key electrostatic interactions in the sHsp dimer provide structural stability and influence both higher-order sHsp interactions and facilitate interactions with substrate proteins that define chaperone holdase activity.
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Affiliation(s)
- Chenwei Wang
- Program in Biochemistry, Mount Holyoke College, South Hadley, MA 01075, USA; (C.W.); (L.T.); (Z.S.L.)
| | - Lilong Teng
- Program in Biochemistry, Mount Holyoke College, South Hadley, MA 01075, USA; (C.W.); (L.T.); (Z.S.L.)
| | - Zhiyan Silvia Liu
- Program in Biochemistry, Mount Holyoke College, South Hadley, MA 01075, USA; (C.W.); (L.T.); (Z.S.L.)
| | - Aichurok Kamalova
- Program in Neuroscience and Behavior, Mount Holyoke College, South Hadley, MA 01075, USA;
| | - Kathryn A. McMenimen
- Program in Biochemistry, Mount Holyoke College, South Hadley, MA 01075, USA; (C.W.); (L.T.); (Z.S.L.)
- Program in Neuroscience and Behavior, Mount Holyoke College, South Hadley, MA 01075, USA;
- Department of Chemistry, Mount Holyoke College, South Hadley, MA 01075, USA
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Chen G, Leppert A, Poska H, Nilsson HE, Alvira CP, Zhong X, Koeck P, Jegerschöld C, Abelein A, Hebert H, Johansson J. Short hydrophobic loop motifs in BRICHOS domains determine chaperone activity against amorphous protein aggregation but not against amyloid formation. Commun Biol 2023; 6:497. [PMID: 37156997 PMCID: PMC10167226 DOI: 10.1038/s42003-023-04883-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Accepted: 04/27/2023] [Indexed: 05/10/2023] Open
Abstract
ATP-independent molecular chaperones are important for maintaining cellular fitness but the molecular determinants for preventing aggregation of partly unfolded protein substrates remain unclear, particularly regarding assembly state and basis for substrate recognition. The BRICHOS domain can perform small heat shock (sHSP)-like chaperone functions to widely different degrees depending on its assembly state and sequence. Here, we observed three hydrophobic sequence motifs in chaperone-active domains, and found that they get surface-exposed when the BRICHOS domain assembles into larger oligomers. Studies of loop-swap variants and site-specific mutants further revealed that the biological hydrophobicities of the three short motifs linearly correlate with the efficiency to prevent amorphous protein aggregation. At the same time, they do not at all correlate with the ability to prevent ordered amyloid fibril formation. The linear correlations also accurately predict activities of chimeras containing short hydrophobic sequence motifs from a sHSP that is unrelated to BRICHOS. Our data indicate that short, exposed hydrophobic motifs brought together by oligomerisation are sufficient and necessary for efficient chaperone activity against amorphous protein aggregation.
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Affiliation(s)
- Gefei Chen
- Department of Biosciences and Nutrition, Karolinska Institutet, 141 83, Huddinge, Sweden.
| | - Axel Leppert
- Department of Biosciences and Nutrition, Karolinska Institutet, 141 83, Huddinge, Sweden
- Department of Microbiology, Tumour and Cell Biology, Karolinska Institutet, 171 65, Solna, Sweden
| | - Helen Poska
- Department of Biosciences and Nutrition, Karolinska Institutet, 141 83, Huddinge, Sweden
- School of Natural Sciences and Health, Tallinn University, Tallinn, Estonia
| | - Harriet E Nilsson
- School of Engineering Sciences in Chemistry, Biotechnology and Health, Department of Biomedical Engineering and Health Systems, KTH Royal Institute of Technology, 141 52, Huddinge, Sweden
| | | | - Xueying Zhong
- School of Engineering Sciences in Chemistry, Biotechnology and Health, Department of Biomedical Engineering and Health Systems, KTH Royal Institute of Technology, 141 52, Huddinge, Sweden
| | - Philip Koeck
- School of Engineering Sciences in Chemistry, Biotechnology and Health, Department of Biomedical Engineering and Health Systems, KTH Royal Institute of Technology, 141 52, Huddinge, Sweden
| | - Caroline Jegerschöld
- School of Engineering Sciences in Chemistry, Biotechnology and Health, Department of Biomedical Engineering and Health Systems, KTH Royal Institute of Technology, 141 52, Huddinge, Sweden
| | - Axel Abelein
- Department of Biosciences and Nutrition, Karolinska Institutet, 141 83, Huddinge, Sweden
| | - Hans Hebert
- School of Engineering Sciences in Chemistry, Biotechnology and Health, Department of Biomedical Engineering and Health Systems, KTH Royal Institute of Technology, 141 52, Huddinge, Sweden
| | - Jan Johansson
- Department of Biosciences and Nutrition, Karolinska Institutet, 141 83, Huddinge, Sweden.
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Multiple nanocages of a cyanophage small heat shock protein with icosahedral and octahedral symmetries. Sci Rep 2021; 11:21023. [PMID: 34697325 PMCID: PMC8546028 DOI: 10.1038/s41598-021-00172-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2021] [Accepted: 09/28/2021] [Indexed: 11/08/2022] Open
Abstract
The structures of a cyanophage small heat shock protein (sHSP) were determined as octahedrons of 24-mers and 48-mers and as icosahedrons of 60-mers. An N-terminal deletion construct of an 18 kDa sHSP of Synechococcus sp. phage S-ShM2 crystallized as a 24-mer and its structure was determined at a resolution of 7 Å. The negative stain electron microscopy (EM) images showed that the full-length protein is a mixture of a major population of larger and a minor population of smaller cage-like particles. Their structures have been determined by electron cryomicroscopy 3D image reconstruction at a resolution of 8 Å. The larger particles are 60-mers with icosahedral symmetry and the smaller ones are 48-mers with octahedral symmetry. These structures are the first of the viral/phage origin and the 60-mer is the largest and the first icosahedral assembly to be reported for sHSPs.
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Reinle K, Mogk A, Bukau B. The Diverse Functions of Small Heat Shock Proteins in the Proteostasis Network. J Mol Biol 2021; 434:167157. [PMID: 34271010 DOI: 10.1016/j.jmb.2021.167157] [Citation(s) in RCA: 48] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Revised: 07/07/2021] [Accepted: 07/08/2021] [Indexed: 01/21/2023]
Abstract
The protein quality control (PQC) system maintains protein homeostasis by counteracting the accumulation of misfolded protein conformers. Substrate degradation and refolding activities executed by ATP-dependent proteases and chaperones constitute major strategies of the proteostasis network. Small heat shock proteins represent ATP-independent chaperones that bind to misfolded proteins, preventing their uncontrolled aggregation. sHsps share the conserved α-crystallin domain (ACD) and gain functional specificity through variable and largely disordered N- and C-terminal extensions (NTE, CTE). They form large, polydisperse oligomers through multiple, weak interactions between NTE/CTEs and ACD dimers. Sequence variations of sHsps and the large variability of sHsp oligomers enable sHsps to fulfill diverse tasks in the PQC network. sHsp oligomers represent inactive yet dynamic resting states that are rapidly deoligomerized and activated upon stress conditions, releasing substrate binding sites in NTEs and ACDs Bound substrates are usually isolated in large sHsp/substrate complexes. This sequestration activity of sHsps represents a third strategy of the proteostasis network. Substrate sequestration reduces the burden for other PQC components during immediate and persistent stress conditions. Sequestered substrates can be released and directed towards refolding pathways by ATP-dependent Hsp70/Hsp100 chaperones or sorted for degradation by autophagic pathways. sHsps can also maintain the dynamic state of phase-separated stress granules (SGs), which store mRNA and translation factors, by reducing the accumulation of misfolded proteins inside SGs and preventing unfolding of SG components. This ensures SG disassembly and regain of translational capacity during recovery periods.
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Affiliation(s)
- Kevin Reinle
- Center for Molecular Biology of the University of Heidelberg (ZMBH), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany; Deutsches Krebsforschungszentrum (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany
| | - Axel Mogk
- Center for Molecular Biology of the University of Heidelberg (ZMBH), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany; Deutsches Krebsforschungszentrum (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany.
| | - Bernd Bukau
- Center for Molecular Biology of the University of Heidelberg (ZMBH), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany; Deutsches Krebsforschungszentrum (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany.
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7
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Butkovich N, Li E, Ramirez A, Burkhardt AM, Wang SW. Advancements in protein nanoparticle vaccine platforms to combat infectious disease. WILEY INTERDISCIPLINARY REVIEWS. NANOMEDICINE AND NANOBIOTECHNOLOGY 2021; 13:e1681. [PMID: 33164326 PMCID: PMC8052270 DOI: 10.1002/wnan.1681] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Revised: 10/04/2020] [Accepted: 10/08/2020] [Indexed: 12/14/2022]
Abstract
Infectious diseases are a major threat to global human health, yet prophylactic treatment options can be limited, as safe and efficacious vaccines exist only for a fraction of all diseases. Notably, devastating diseases such as acquired immunodeficiency syndrome (AIDS) and coronavirus disease of 2019 (COVID-19) currently do not have vaccine therapies. Conventional vaccine platforms, such as live attenuated vaccines and whole inactivated vaccines, can be difficult to manufacture, may cause severe side effects, and can potentially induce severe infection. Subunit vaccines carry far fewer safety concerns due to their inability to cause vaccine-based infections. The applicability of protein nanoparticles (NPs) as vaccine scaffolds is promising to prevent infectious diseases, and they have been explored for a number of viral, bacterial, fungal, and parasitic diseases. Many types of protein NPs exist, including self-assembling NPs, bacteriophage-derived NPs, plant virus-derived NPs, and human virus-based vectors, and these particular categories will be covered in this review. These vaccines can elicit strong humoral and cellular immune responses against specific pathogens, as well as provide protection against infection in a number of animal models. Furthermore, published clinical trials demonstrate the promise of applying these NP vaccine platforms, which include bacteriophage-derived NPs, in addition to multiple viral vectors that are currently used in the clinic. The continued investigations of protein NP vaccine platforms are critical to generate safer alternatives to current vaccines, advance vaccines for diseases that currently lack effective prophylactic therapies, and prepare for the rapid development of new vaccines against emerging infectious diseases. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.
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Affiliation(s)
- Nina Butkovich
- Department of Chemical and Biomolecular Engineering, University of California, Irvine, CA 92697 USA
| | - Enya Li
- Department of Chemical and Biomolecular Engineering, University of California, Irvine, CA 92697 USA
| | - Aaron Ramirez
- Department of Chemical and Biomolecular Engineering, University of California, Irvine, CA 92697 USA
| | - Amanda M. Burkhardt
- Department of Clinical Pharmacy, School of Pharmacy, University of Southern California, Los Angeles, CA 90089 USA
| | - Szu-Wen Wang
- Department of Chemical and Biomolecular Engineering, University of California, Irvine, CA 92697 USA
- Department of Biomedical Engineering, University of California, Irvine, CA 92697 USA
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Mogk A, Ruger-Herreros C, Bukau B. Cellular Functions and Mechanisms of Action of Small Heat Shock Proteins. Annu Rev Microbiol 2019; 73:89-110. [PMID: 31091419 DOI: 10.1146/annurev-micro-020518-115515] [Citation(s) in RCA: 99] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Small heat shock proteins (sHsps) constitute a diverse chaperone family that shares the α-crystallin domain, which is flanked by variable, disordered N- and C-terminal extensions. sHsps act as the first line of cellular defense against protein unfolding stress. They form dynamic, large oligomers that represent inactive storage forms. Stress conditions cause a rapid increase in cellular sHsp levels and trigger conformational rearrangements, resulting in exposure of substrate-binding sites and sHsp activation. sHsps bind to early-unfolding intermediates of misfolding proteins in an ATP-independent manner and sequester them in sHsp/substrate complexes. Sequestration protects substrates from further uncontrolled aggregation and facilitates their refolding by ATP-dependent Hsp70-Hsp100 disaggregases. Some sHsps with particularly strong sequestrase activity, such as yeast Hsp42, are critical factors for forming large, microscopically visible deposition sites of misfolded proteins in vivo. These sites are organizing centers for triaging substrates to distinct quality control pathways, preferentially Hsp70-dependent refolding and selective autophagy.
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Affiliation(s)
- Axel Mogk
- Center for Molecular Biology of the University of Heidelberg and German Cancer Research Center, DKFZ-ZMBH Alliance, 69120 Heidelberg, Germany; ,
| | - Carmen Ruger-Herreros
- Center for Molecular Biology of the University of Heidelberg and German Cancer Research Center, DKFZ-ZMBH Alliance, 69120 Heidelberg, Germany; ,
| | - Bernd Bukau
- Center for Molecular Biology of the University of Heidelberg and German Cancer Research Center, DKFZ-ZMBH Alliance, 69120 Heidelberg, Germany; ,
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Bhandari S, Biswas S, Chaudhary A, Dutta S, Suguna K. Dodecameric structure of a small heat shock protein from Mycobacterium marinum M. Proteins 2019; 87:365-379. [PMID: 30632633 DOI: 10.1002/prot.25657] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Revised: 12/24/2018] [Accepted: 01/05/2019] [Indexed: 12/31/2022]
Abstract
Small heat shock proteins (sHSPs) are ATP-independent molecular chaperones present ubiquitously in all kingdoms of life. Their low molecular weight subunits associate to form higher order structures. Under conditions of stress, sHSPs prevent aggregation of substrate proteins by undergoing rapid changes in their conformation or stoichiometry. Polydispersity and dynamic nature of these proteins have made structural investigations through crystallography a daunting task. In pathogens like Mycobacteria, sHSPs are immuno-dominant antigens, enabling survival of the pathogen within the host and contributing to disease persistence. We characterized sHSPs from Mycobacterium marinum M and determined the crystal structure of one of these. The protein crystallized in three different conditions as dodecamers, with dimers arranged in a tetrahedral fashion to form a closed cage-like architecture. Interestingly, we found a pentapeptide bound to the dodecamers revealing one of the modes of sHSP-substrate interaction. Further, we have observed that ATP inhibits the chaperoning activity of the protein.
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Affiliation(s)
- Spraha Bhandari
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
| | - Sreeparna Biswas
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
| | - Anuradha Chaudhary
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
| | - Somnath Dutta
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
| | - Kaza Suguna
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
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Haslbeck M, Weinkauf S, Buchner J. Small heat shock proteins: Simplicity meets complexity. J Biol Chem 2018; 294:2121-2132. [PMID: 30385502 DOI: 10.1074/jbc.rev118.002809] [Citation(s) in RCA: 165] [Impact Index Per Article: 27.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Small heat shock proteins (sHsps) are a ubiquitous and ancient family of ATP-independent molecular chaperones. A key characteristic of sHsps is that they exist in ensembles of iso-energetic oligomeric species differing in size. This property arises from a unique mode of assembly involving several parts of the subunits in a flexible manner. Current evidence suggests that smaller oligomers are more active chaperones. Thus, a shift in the equilibrium of the sHsp ensemble allows regulating the chaperone activity. Different mechanisms have been identified that reversibly change the oligomer equilibrium. The promiscuous interaction with non-native proteins generates complexes that can form aggregate-like structures from which native proteins are restored by ATP-dependent chaperones such as Hsp70 family members. In recent years, this basic paradigm has been expanded, and new roles and new cofactors, as well as variations in structure and regulation of sHsps, have emerged.
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Affiliation(s)
- Martin Haslbeck
- From the Department of Chemie and Center for Integrated Protein Science, Technische Universität München, Lichtenbergstrasse 4, 85 748 Garching, Germany
| | - Sevil Weinkauf
- From the Department of Chemie and Center for Integrated Protein Science, Technische Universität München, Lichtenbergstrasse 4, 85 748 Garching, Germany
| | - Johannes Buchner
- From the Department of Chemie and Center for Integrated Protein Science, Technische Universität München, Lichtenbergstrasse 4, 85 748 Garching, Germany
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11
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Santhanagopalan I, Degiacomi MT, Shepherd DA, Hochberg GKA, Benesch JLP, Vierling E. It takes a dimer to tango: Oligomeric small heat shock proteins dissociate to capture substrate. J Biol Chem 2018; 293:19511-19521. [PMID: 30348902 DOI: 10.1074/jbc.ra118.005421] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2018] [Revised: 10/12/2018] [Indexed: 12/23/2022] Open
Abstract
Small heat-shock proteins (sHsps) are ubiquitous molecular chaperones, and sHsp mutations or altered expression are linked to multiple human disease states. sHsp monomers assemble into large oligomers with dimeric substructure, and the dynamics of sHsp oligomers has led to major questions about the form that captures substrate, a critical aspect of their mechanism of action. We show here that substructural dimers of two plant dodecameric sHsps, Ta16.9 and homologous Ps18.1, are functional units in the initial encounter with unfolding substrate. We introduced inter-polypeptide disulfide bonds at the two dodecameric interfaces, dimeric and nondimeric, to restrict how their assemblies can dissociate. When disulfide-bonded at the nondimeric interface, mutants of Ta16.9 and Ps18.1 (TaCT-ACD and PsCT-ACD) were inactive but, when reduced, had WT-like chaperone activity, demonstrating that dissociation at nondimeric interfaces is essential for sHsp activity. Moreover, the size of the TaCT-ACD and PsCT-ACD covalent unit defined a new tetrahedral geometry for these sHsps, different from that observed in the Ta16.9 X-ray structure. Importantly, oxidized Tadimer (disulfide bonded at the dimeric interface) exhibited greatly enhanced ability to protect substrate, indicating that strengthening the dimeric interface increases chaperone efficiency. Temperature-induced size and secondary structure changes revealed that folded sHsp dimers interact with substrate and that dimer stability affects chaperone efficiency. These results yield a model in which sHsp dimers capture substrate before assembly into larger, heterogeneous sHsp-substrate complexes for substrate refolding or degradation, and suggest that tuning the strength of the dimer interface can be used to engineer sHsp chaperone efficiency.
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Affiliation(s)
- Indu Santhanagopalan
- From the Department of Biochemistry and Molecular Biology, University of Massachusetts Amherst, Amherst, Massachusetts 01003
| | - Matteo T Degiacomi
- Department of Chemistry, Physical & Theoretical Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford, OX1 3TA, United Kingdom, and.,Department of Chemistry, Durham University, South Road, Durham, DH1 3LE, United Kingdom
| | - Dale A Shepherd
- Department of Chemistry, Physical & Theoretical Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford, OX1 3TA, United Kingdom, and
| | - Georg K A Hochberg
- Department of Chemistry, Physical & Theoretical Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford, OX1 3TA, United Kingdom, and
| | - Justin L P Benesch
- Department of Chemistry, Physical & Theoretical Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford, OX1 3TA, United Kingdom, and
| | - Elizabeth Vierling
- From the Department of Biochemistry and Molecular Biology, University of Massachusetts Amherst, Amherst, Massachusetts 01003,
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12
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Scapin G, Potter CS, Carragher B. Cryo-EM for Small Molecules Discovery, Design, Understanding, and Application. Cell Chem Biol 2018; 25:1318-1325. [PMID: 30100349 DOI: 10.1016/j.chembiol.2018.07.006] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2018] [Revised: 05/11/2018] [Accepted: 07/05/2018] [Indexed: 12/13/2022]
Abstract
We present a perspective of our view of the application of cryoelectron microscopy (cryo-EM) to structure-based drug design (SBDD). We discuss the basic needs and requirements for SBDD, the current state of cryo-EM, and the challenges that need to be overcome for this technique to reach its full potential in facilitating the process of drug discovery.
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Affiliation(s)
- Giovanna Scapin
- Department of Biochemical Engineering & Structure, Merck & Co., Inc., 2000 Galloping Hill Rd., Kenilworth, NJ 07033, USA
| | - Clinton S Potter
- Simons Electron Microscopy Center, National Resource for Automated Molecular Microscopy, New York Structural Biology Center, 89 Convent Avenue, New York NY 10027, USA; NanoImaging Services, 4940 Carroll Canyon Road, Suite 115, San Diego, CA 92121, USA
| | - Bridget Carragher
- Simons Electron Microscopy Center, National Resource for Automated Molecular Microscopy, New York Structural Biology Center, 89 Convent Avenue, New York NY 10027, USA; NanoImaging Services, 4940 Carroll Canyon Road, Suite 115, San Diego, CA 92121, USA.
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13
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Mishra S, Chandler SA, Williams D, Claxton DP, Koteiche HA, Stewart PL, Benesch JLP, Mchaourab HS. Engineering of a Polydisperse Small Heat-Shock Protein Reveals Conserved Motifs of Oligomer Plasticity. Structure 2018; 26:1116-1126.e4. [PMID: 29983375 DOI: 10.1016/j.str.2018.05.015] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2017] [Revised: 04/10/2018] [Accepted: 05/18/2018] [Indexed: 01/21/2023]
Abstract
Small heat-shock proteins (sHSPs) are molecular chaperones that bind partially and globally unfolded states of their client proteins. Previously, we discovered that the archaeal Hsp16.5, which forms ordered and symmetric 24-subunit oligomers, can be engineered to transition to an ordered and symmetric 48-subunit oligomer by insertion of a peptide from human HspB1 (Hsp27). Here, we uncovered the existence of an array of oligomeric states (30-38 subunits) that can be populated as a consequence of altering the sequence and length of the inserted peptide. Polydisperse Hsp16.5 oligomers displayed higher affinity to a model client protein consistent with a general mechanism for recognition and binding that involves increased access of the hydrophobic N-terminal region. Our findings, which integrate structural and functional analyses from evolutionarily distant sHSPs, support a model wherein the modular architecture of these proteins encodes motifs of oligomer polydispersity, dissociation, and expansion to achieve functional diversity and regulation.
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Affiliation(s)
- Sanjay Mishra
- Chemical & Physical Biology Program, Vanderbilt University, Nashville 37232, TN, USA; Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville 37232, TN, USA
| | - Shane A Chandler
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, UK
| | - Dewight Williams
- John M. Cowley Center for High Resolution Electron Microscopy, Arizona State University, Tempe 85287, AZ, USA
| | - Derek P Claxton
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville 37232, TN, USA
| | - Hanane A Koteiche
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville 37232, TN, USA
| | - Phoebe L Stewart
- Department of Pharmacology Case Western Reserve University, Cleveland, OH 44106, USA
| | | | - Hassane S Mchaourab
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville 37232, TN, USA.
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14
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Mishra S, Wu SY, Fuller AW, Wang Z, Rose KL, Schey KL, Mchaourab HS. Loss of αB-crystallin function in zebrafish reveals critical roles in the development of the lens and stress resistance of the heart. J Biol Chem 2017; 293:740-753. [PMID: 29162721 DOI: 10.1074/jbc.m117.808634] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2017] [Revised: 11/17/2017] [Indexed: 12/12/2022] Open
Abstract
Genetic mutations in the human small heat shock protein αB-crystallin have been implicated in autosomal cataracts and skeletal myopathies, including heart muscle diseases (cardiomyopathy). Although these mutations lead to modulation of their chaperone activity in vitro, the in vivo functions of αB-crystallin in the maintenance of both lens transparency and muscle integrity remain unclear. This lack of information has hindered a mechanistic understanding of these diseases. To better define the functional roles of αB-crystallin, we generated loss-of-function zebrafish mutant lines by utilizing the CRISPR/Cas9 system to specifically disrupt the two αB-crystallin genes, αBa and αBb We observed lens abnormalities in the mutant lines of both genes, and the penetrance of the lens phenotype was higher in αBa than αBb mutants. This finding is in contrast with the lack of a phenotype previously reported in αB-crystallin knock-out mice and suggests that the elevated chaperone activity of the two zebrafish orthologs is critical for lens development. Besides its key role in the lens, we uncovered another critical role for αB-crystallin in providing stress tolerance to the heart. The αB-crystallin mutants exhibited hypersusceptibility to develop pericardial edema when challenged by crowding stress or exposed to elevated cortisol stress, both of which activate glucocorticoid receptor signaling. Our work illuminates the involvement of αB-crystallin in stress tolerance of the heart presumably through the proteostasis network and reinforces the critical role of the chaperone activity of αB-crystallin in the maintenance of lens transparency.
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Affiliation(s)
- Sanjay Mishra
- From the Departments of Molecular Physiology and Biophysics and
| | - Shu-Yu Wu
- From the Departments of Molecular Physiology and Biophysics and
| | | | - Zhen Wang
- Biochemistry and.,Mass Spectrometry Research Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232
| | - Kristie L Rose
- Biochemistry and.,Mass Spectrometry Research Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232
| | - Kevin L Schey
- Biochemistry and.,Mass Spectrometry Research Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232
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15
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Carra S, Alberti S, Arrigo PA, Benesch JL, Benjamin IJ, Boelens W, Bartelt-Kirbach B, Brundel BJJM, Buchner J, Bukau B, Carver JA, Ecroyd H, Emanuelsson C, Finet S, Golenhofen N, Goloubinoff P, Gusev N, Haslbeck M, Hightower LE, Kampinga HH, Klevit RE, Liberek K, Mchaourab HS, McMenimen KA, Poletti A, Quinlan R, Strelkov SV, Toth ME, Vierling E, Tanguay RM. The growing world of small heat shock proteins: from structure to functions. Cell Stress Chaperones 2017; 22:601-611. [PMID: 28364346 PMCID: PMC5465036 DOI: 10.1007/s12192-017-0787-8] [Citation(s) in RCA: 118] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/15/2017] [Indexed: 12/21/2022] Open
Abstract
Small heat shock proteins (sHSPs) are present in all kingdoms of life and play fundamental roles in cell biology. sHSPs are key components of the cellular protein quality control system, acting as the first line of defense against conditions that affect protein homeostasis and proteome stability, from bacteria to plants to humans. sHSPs have the ability to bind to a large subset of substrates and to maintain them in a state competent for refolding or clearance with the assistance of the HSP70 machinery. sHSPs participate in a number of biological processes, from the cell cycle, to cell differentiation, from adaptation to stressful conditions, to apoptosis, and, even, to the transformation of a cell into a malignant state. As a consequence, sHSP malfunction has been implicated in abnormal placental development and preterm deliveries, in the prognosis of several types of cancer, and in the development of neurological diseases. Moreover, mutations in the genes encoding several mammalian sHSPs result in neurological, muscular, or cardiac age-related diseases in humans. Loss of protein homeostasis due to protein aggregation is typical of many age-related neurodegenerative and neuromuscular diseases. In light of the role of sHSPs in the clearance of un/misfolded aggregation-prone substrates, pharmacological modulation of sHSP expression or function and rescue of defective sHSPs represent possible routes to alleviate or cure protein conformation diseases. Here, we report the latest news and views on sHSPs discussed by many of the world's experts in the sHSP field during a dedicated workshop organized in Italy (Bertinoro, CEUB, October 12-15, 2016).
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Affiliation(s)
- Serena Carra
- Department of Biomedical, Metabolic and Neural Sciences, and Centre for Neuroscience and Neurotechnology, University of Modena and Reggio Emilia, via G. Campi 287, 41125 Modena, Italy
| | - Simon Alberti
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Patrick A. Arrigo
- Université de Lyon, 69622 Lyon, France
- CNRS, UMR 5310, INSERM U1217, Institut NeuroMyoGène, Université Lyon 1, 69100 Villeurbanne, France
| | | | - Ivor J. Benjamin
- Department of Biochemistry, University of Utah, Salt Lake City, UT 84112-5650 USA
| | - Wilbert Boelens
- Biomolecular Chemistry, 284, Radboud University, PO Box 9101, 6500 HB Nijmegen, The Netherlands
| | | | - Bianca J. J. M. Brundel
- Department of Clinical Pharmacy and Pharmacology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
- Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands
| | | | - Bernd Bukau
- Center for Molecular Biology of the University of Heidelberg (ZMBH), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany
- German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany
| | - John A. Carver
- The Research School of Chemistry, The Australian National University, Acton, ACT 2601 Australia
| | - Heath Ecroyd
- Illawara Health and Medical Research Institute, School of Biological Sciences, University of Wollongong, Wollongong, NSW 2522 Australia
| | - Cecilia Emanuelsson
- Department of Biochemistry and Structural Biology, Center for Molecular Protein Science, Lund University, 221 00 Lund, Sweden
| | - Stephanie Finet
- IMPMC UMR7590, CNRS, UPMC Paris 6, 4 place Jussieu, Paris, France
| | - Nikola Golenhofen
- Institute of Anatomy and Cell Biology, University of Ulm, 89081 Ulm, Germany
| | - Pierre Goloubinoff
- Department of Plant Molecular Biology, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland
| | - Nikolai Gusev
- Department of Biochemistry, School of Biology, Moscow State University, Moscow, 119991 Russia
| | | | - Lawrence E. Hightower
- Department of Molecular & Cell Biology, University of Connecticut, 91 North Eagleville Road, Storrs, CT 06269-3125 USA
| | - Harm H. Kampinga
- Department of Cell Biology, University Medical Center Groningen, University of Groningen, 9713 GZ Groningen, The Netherlands
| | - Rachel E. Klevit
- Department of Biochemistry, University of Washington, Seattle, WA 98195 USA
| | - Krzysztof Liberek
- Department of Molecular and Cellular Biology, Intercollegiate Faculty of Biotechnology, University of Gdańsk and the Medical University of Gdańsk, Gdańsk, Poland
| | - Hassane S. Mchaourab
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232 USA
| | - Kathryn A. McMenimen
- Departments of Pathology, Biological Chemistry, and Medicinal Chemistry and the Life Sciences Institute, University of Michigan, Ann Arbor, MI USA
| | - Angelo Poletti
- Dipartimento di Scienze Farmacologiche e Biomolecolari (DiSFeB), Centro di Eccellenza sulle Malattie Neurodegenerative, Università degli Studi di Milano, Milan, Italy
| | - Roy Quinlan
- Department of Biosciences and the Biophysical Sciences Institute, University of Durham, Durham, UK
| | - Sergei V. Strelkov
- Laboratory for Biocrystallography, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Leuven, Belgium
| | - Melinda E. Toth
- Laboratory of Animal Genetics and Molecular Neurobiology, Institute of Biochemistry, Biological Research Centre, Szeged, Hungary
| | - Elizabeth Vierling
- Biochemistry and Molecular Biology, University of Massachusetts, Amherst, MA 01003 USA
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721 USA
| | - Robert M. Tanguay
- Laboratory of Cell & Developmental Genetics, IBIS, and Department of Molecular Biology, Medical Biochemistry and Pathology, Medical School, Université Laval, Québec (Qc), G1V 0A6 Canada
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16
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Żwirowski S, Kłosowska A, Obuchowski I, Nillegoda NB, Piróg A, Ziętkiewicz S, Bukau B, Mogk A, Liberek K. Hsp70 displaces small heat shock proteins from aggregates to initiate protein refolding. EMBO J 2017; 36:783-796. [PMID: 28219929 DOI: 10.15252/embj.201593378] [Citation(s) in RCA: 100] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2015] [Revised: 01/12/2017] [Accepted: 01/16/2017] [Indexed: 11/09/2022] Open
Abstract
Small heat shock proteins (sHsps) are an evolutionary conserved class of ATP-independent chaperones that protect cells against proteotoxic stress. sHsps form assemblies with aggregation-prone misfolded proteins, which facilitates subsequent substrate solubilization and refolding by ATP-dependent Hsp70 and Hsp100 chaperones. Substrate solubilization requires disruption of sHsp association with trapped misfolded proteins. Here, we unravel a specific interplay between Hsp70 and sHsps at the initial step of the solubilization process. We show that Hsp70 displaces surface-bound sHsps from sHsp-substrate assemblies. This Hsp70 activity is unique among chaperones and highly sensitive to alterations in Hsp70 concentrations. The Hsp70 activity is reflected in the organization of sHsp-substrate assemblies, including an outer dynamic sHsp shell that is removed by Hsp70 and a stable core comprised mainly of aggregated substrates. Binding of Hsp70 to the sHsp/substrate core protects the core from aggregation and directs sequestered substrates towards refolding pathway. The sHsp/Hsp70 interplay has major impact on protein homeostasis as it sensitizes substrate release towards cellular Hsp70 availability ensuring efficient refolding of damaged proteins under favourable folding conditions.
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Affiliation(s)
- Szymon Żwirowski
- Department of Molecular and Cellular Biology, Intercollegiate Faculty of Biotechnology UG-MUG, University of Gdansk, Gdansk, Poland
| | - Agnieszka Kłosowska
- Department of Molecular and Cellular Biology, Intercollegiate Faculty of Biotechnology UG-MUG, University of Gdansk, Gdansk, Poland
| | - Igor Obuchowski
- Department of Molecular and Cellular Biology, Intercollegiate Faculty of Biotechnology UG-MUG, University of Gdansk, Gdansk, Poland
| | - Nadinath B Nillegoda
- Center for Molecular Biology, University of Heidelberg (ZMBH), Heidelberg, Germany.,German Cancer Research Centre (DKFZ), DKFZ-ZMBH Alliance, Heidelberg, Germany
| | - Artur Piróg
- Department of Molecular and Cellular Biology, Intercollegiate Faculty of Biotechnology UG-MUG, University of Gdansk, Gdansk, Poland
| | - Szymon Ziętkiewicz
- Department of Molecular and Cellular Biology, Intercollegiate Faculty of Biotechnology UG-MUG, University of Gdansk, Gdansk, Poland
| | - Bernd Bukau
- Center for Molecular Biology, University of Heidelberg (ZMBH), Heidelberg, Germany.,German Cancer Research Centre (DKFZ), DKFZ-ZMBH Alliance, Heidelberg, Germany
| | - Axel Mogk
- Center for Molecular Biology, University of Heidelberg (ZMBH), Heidelberg, Germany.,German Cancer Research Centre (DKFZ), DKFZ-ZMBH Alliance, Heidelberg, Germany
| | - Krzysztof Liberek
- Department of Molecular and Cellular Biology, Intercollegiate Faculty of Biotechnology UG-MUG, University of Gdansk, Gdansk, Poland
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17
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The function of small heat-shock proteins and their implication in proteostasis. Essays Biochem 2016; 60:163-172. [DOI: 10.1042/ebc20160010] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2016] [Accepted: 04/15/2016] [Indexed: 11/17/2022]
Abstract
All organisms rely on a conserved cellular machinery supporting and controlling the life cycle of proteins: the proteostasis network. Within this network, the main players that determine the fate of proteins are molecular chaperones, the ubiquitin–proteasome and the lysosome–autophagy systems. sHsps (small heat-shock proteins) represent one family of molecular chaperones found in all domains of life. They prevent irreversible aggregation of unfolded proteins and maintain proteostasis by stabilizing promiscuously a variety of non-native proteins in an ATP-independent manner. In the cellular chaperone network, sHsps act as the first line of defence and keep their substrates in a folding-competent state until they are refolded by downstream ATP-dependent chaperone systems. Besides this interaction with unfolding substrates upon stress, sHsps show a different mode of binding for specific clients which are also recognized under physiological conditions. In vertebrates, sHsps are especially needed to maintain the refractive index of the eye lens. Additionally, sHsps are linked to a broad variety of diseases such as myopathies and neuropathies. The most striking feature of sHsps is their ability to form dynamic ensembles of higher oligomers. The activity of sHsps is regulated by changes in the composition of the ensembles.
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18
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Mani N, Bhandari S, Moreno R, Hu L, Prasad BVV, Suguna K. Multiple oligomeric structures of a bacterial small heat shock protein. Sci Rep 2016; 6:24019. [PMID: 27053150 PMCID: PMC4823740 DOI: 10.1038/srep24019] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2015] [Accepted: 03/14/2016] [Indexed: 11/23/2022] Open
Abstract
Small heat shock proteins are ubiquitous molecular chaperones that form the first line of defence against the detrimental effects of cellular stress. Under conditions of stress they undergo drastic conformational rearrangements in order to bind to misfolded substrate proteins and prevent cellular protein aggregation. Owing to the dynamic nature of small heat shock protein oligomers, elucidating the structural basis of chaperone action and oligomerization still remains a challenge. In order to understand the organization of sHSP oligomers, we have determined crystal structures of a small heat shock protein from Salmonella typhimurium in a dimeric form and two higher oligomeric forms: an 18-mer and a 24-mer. Though the core dimer structure is conserved in all the forms, structural heterogeneity arises due to variation in the terminal regions.
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Affiliation(s)
- Nandini Mani
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
| | - Spraha Bhandari
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
| | - Rodolfo Moreno
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, United States
| | - Liya Hu
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, United States
| | - B V Venkataram Prasad
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, United States
| | - Kaza Suguna
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
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19
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Small Heat Shock Proteins, a Key Player in Grass Plant Thermotolerance. HEAT SHOCK PROTEINS AND PLANTS 2016. [DOI: 10.1007/978-3-319-46340-7_3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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20
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The chaperone αB-crystallin uses different interfaces to capture an amorphous and an amyloid client. Nat Struct Mol Biol 2015; 22:898-905. [PMID: 26458046 DOI: 10.1038/nsmb.3108] [Citation(s) in RCA: 114] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2015] [Accepted: 09/11/2015] [Indexed: 12/20/2022]
Abstract
Small heat-shock proteins, including αB-crystallin (αB), play an important part in protein homeostasis, because their ATP-independent chaperone activity inhibits uncontrolled protein aggregation. Mechanistic details of human αB, particularly in its client-bound state, have been elusive so far, owing to the high molecular weight and the heterogeneity of these complexes. Here we provide structural insights into this highly dynamic assembly and show, by using state-of-the-art NMR spectroscopy, that the αB complex is assembled from asymmetric building blocks. Interaction studies demonstrated that the fibril-forming Alzheimer's disease Aβ1-40 peptide preferentially binds to a hydrophobic edge of the central β-sandwich of αB. In contrast, the amorphously aggregating client lysozyme is captured by the partially disordered N-terminal domain of αB. We suggest that αB uses its inherent structural plasticity to expose distinct binding interfaces and thus interact with a wide range of structurally variable clients.
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21
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Liu L, Chen JY, Yang B, Wang FH, Wang YH, Yun CH. Active-State Structures of a Small Heat-Shock Protein Revealed a Molecular Switch for Chaperone Function. Structure 2015; 23:2066-75. [PMID: 26439766 DOI: 10.1016/j.str.2015.08.015] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2015] [Revised: 08/27/2015] [Accepted: 08/29/2015] [Indexed: 01/09/2023]
Abstract
Small heat-shock proteins (sHsps) maintain cellular homeostasis by binding to denatured client proteins to prevent aggregation. Numerous studies indicate that the N-terminal domain (NTD) of sHsps is responsible for binding to client proteins, but the binding mechanism and chaperone activity regulation remain elusive. Here, we report the crystal structures of the wild-type and mutants of an sHsp from Sulfolobus solfataricus representing the inactive and active state of this protein, respectively. All three structures reveal well-defined NTD, but their conformations are remarkably different. The mutant NTDs show disrupted helices presenting a reformed hydrophobic surface compatible with recognizing client proteins. Our functional data show that mutating key hydrophobic residues in this region drastically altered the chaperone activity of this sHsp. These data suggest a new model in which a molecular switch located in NTD facilitates conformational changes for client protein binding.
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Affiliation(s)
- Liang Liu
- Institute of Systems Biomedicine, Department of Biophysics, Beijing Key Laboratory of Tumor Systems Biology and Center for Molecular and Translational Medicine, School of Basic Medical Sciences, Peking University Health Science Center, Beijing 100191, P.R. China; School of Bioscience and Bioengineering, South China University of Technology, Guangzhou 510006, P.R. China; Co-first author
| | - Ji-Yun Chen
- Institute of Systems Biomedicine, Department of Biophysics, Beijing Key Laboratory of Tumor Systems Biology and Center for Molecular and Translational Medicine, School of Basic Medical Sciences, Peking University Health Science Center, Beijing 100191, P.R. China; Co-first author
| | - Bo Yang
- School of Bioscience and Bioengineering, South China University of Technology, Guangzhou 510006, P.R. China
| | - Fang-Hua Wang
- College of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510641, P.R. China
| | - Yong-Hua Wang
- College of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510641, P.R. China.
| | - Cai-Hong Yun
- Institute of Systems Biomedicine, Department of Biophysics, Beijing Key Laboratory of Tumor Systems Biology and Center for Molecular and Translational Medicine, School of Basic Medical Sciences, Peking University Health Science Center, Beijing 100191, P.R. China.
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22
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Koteiche HA, Claxton DP, Mishra S, Stein RA, McDonald ET, Mchaourab HS. Species-Specific Structural and Functional Divergence of α-Crystallins: Zebrafish αBa- and Rodent αA(ins)-Crystallin Encode Activated Chaperones. Biochemistry 2015; 54:5949-58. [PMID: 26378715 DOI: 10.1021/acs.biochem.5b00678] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In addition to contributing to lens optical properties, the α-crystallins are small heat shock proteins that possess chaperone activity and are predicted to bind and sequester destabilized proteins to delay cataract formation. The current model of α-crystallin chaperone mechanism envisions a transition from the native oligomer to an activated form that has higher affinity to non-native states of the substrate. Previous studies have suggested that this oligomeric plasticity is encoded in the primary sequence and controls access to high affinity binding sites within the N-terminal domain. Here, we further examined the role of sequence variation in the context of species-specific α-crystallins from rat and zebrafish. Alternative splicing of the αA gene in rodents produces αA(ins), which is distinguished by a longer N-terminal domain. The zebrafish genome includes duplicate αB-crystallin genes, αBa and αBb, which display divergent primary sequence and tissue expression patterns. Equilibrium binding experiments were employed to quantitatively define chaperone interactions with a destabilized model substrate, T4 lysozyme. In combination with multiangle light scattering, we show that rat αA(ins) and zebrafish α-crystallins display distinct global structural properties and chaperone activities. Notably, we find that αA(ins) and αBa demonstrate substantially enhanced chaperone function relative to other α-crystallins, binding the same substrate more than 2 orders of magnitude higher affinity and mimicking the activity of fully activated mammalian small heat shock proteins. These results emphasize the role of sequence divergence as an evolutionary strategy to tune chaperone function to the requirements of the tissues and organisms in which they are expressed.
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Affiliation(s)
- Hanane A Koteiche
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine , Nashville, Tennessee 37232, United States
| | - Derek P Claxton
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine , Nashville, Tennessee 37232, United States
| | - Sanjay Mishra
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine , Nashville, Tennessee 37232, United States
| | - Richard A Stein
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine , Nashville, Tennessee 37232, United States
| | - Ezelle T McDonald
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine , Nashville, Tennessee 37232, United States
| | - Hassane S Mchaourab
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine , Nashville, Tennessee 37232, United States
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23
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Mymrikov EV, Haslbeck M. Medical implications of understanding the functions of human small heat shock proteins. Expert Rev Proteomics 2015; 12:295-308. [PMID: 25915440 DOI: 10.1586/14789450.2015.1039993] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Small heat shock proteins (sHsps) are ubiquitous molecular chaperones that are implicated in a variety of diseases. Upon stress, they stabilize unfolding proteins and prevent them from aggregating. However, under physiological conditions without severe stress, some sHsps interact with other proteins. In a perspective view, their ability to bind specific client proteins might allow them to fine-tune the availability of the client for other, client-dependent cellular processes. Additionally, some sHsps seem to interact with specific co-chaperones. These co-chaperones are usually part of large protein machineries that are functionally modulated upon sHsps interaction. Finally, secreted human sHsps seem to interact with receptor proteins, potentially as signal molecules transmitting the stress status from one cell to another. This review focuses on the mechanistic description of these different binding modes for human sHsps and how this might help to understand and modulate the function of sHsps in the context of disease.
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Affiliation(s)
- Evgeny V Mymrikov
- Department Chemie, Technische Universität München, D-85747 Garching, Germany
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24
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Oligomer-dependent and -independent chaperone activity of sHsps in different stressed conditions. FEBS Open Bio 2015; 5:155-62. [PMID: 25834780 PMCID: PMC4359974 DOI: 10.1016/j.fob.2015.02.006] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2014] [Revised: 02/20/2015] [Accepted: 02/28/2015] [Indexed: 12/12/2022] Open
Abstract
A great number of studies have proven that sHsps protect cells by inhibiting protein aggregation under heat stress, while little is known about their function to protect cells under acid stress. In this work, we show that Hsp20.1 and Hsp14.1 oligomers dissociated to smaller oligomeric species or even dimer/monomer at low pH (pH 4.0 and pH 2.0), whereas no prominent quaternary structural changes were seen at 50 °C. Both oligomers and smaller oligomeric species exhibited abilities to suppress client aggregation at low pH and at 50 °C. These results suggest that sHsps may function in different modes in different stressed conditions.
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25
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Liu L, Chen J, Yang B, Wang Y. Crystal structure and function of an unusual dimeric Hsp20.1 provide insight into the thermal protection mechanism of small heat shock proteins. Biochem Biophys Res Commun 2015; 458:429-34. [DOI: 10.1016/j.bbrc.2015.01.134] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2015] [Accepted: 01/26/2015] [Indexed: 01/01/2023]
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26
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Haslbeck M, Vierling E. A first line of stress defense: small heat shock proteins and their function in protein homeostasis. J Mol Biol 2015; 427:1537-48. [PMID: 25681016 DOI: 10.1016/j.jmb.2015.02.002] [Citation(s) in RCA: 380] [Impact Index Per Article: 42.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2015] [Revised: 02/03/2015] [Accepted: 02/04/2015] [Indexed: 10/24/2022]
Abstract
Small heat shock proteins (sHsps) are virtually ubiquitous molecular chaperones that can prevent the irreversible aggregation of denaturing proteins. sHsps complex with a variety of non-native proteins in an ATP-independent manner and, in the context of the stress response, form a first line of defense against protein aggregation in order to maintain protein homeostasis. In vertebrates, they act to maintain the clarity of the eye lens, and in humans, sHsp mutations are linked to myopathies and neuropathies. Although found in all domains of life, sHsps are quite diverse and have evolved independently in metazoans, plants and fungi. sHsp monomers range in size from approximately 12 to 42kDa and are defined by a conserved β-sandwich α-crystallin domain, flanked by variable N- and C-terminal sequences. Most sHsps form large oligomeric ensembles with a broad distribution of different, sphere- or barrel-like oligomers, with the size and structure of the oligomers dictated by features of the N- and C-termini. The activity of sHsps is regulated by mechanisms that change the equilibrium distribution in tertiary features and/or quaternary structure of the sHsp ensembles. Cooperation and/or co-assembly between different sHsps in the same cellular compartment add an underexplored level of complexity to sHsp structure and function.
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Affiliation(s)
- Martin Haslbeck
- Department Chemie, Technische Universität München, Lichtenbergstrasse 4, 85 748 Garching, Germany.
| | - Elizabeth Vierling
- Department of Biochemistry and Molecular Biology, University of Massachusetts, Life Science Laboratories, N329 240 Thatcher Road, Amherst, MA 01003-9364, USA.
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Treweek TM, Meehan S, Ecroyd H, Carver JA. Small heat-shock proteins: important players in regulating cellular proteostasis. Cell Mol Life Sci 2015; 72:429-451. [PMID: 25352169 PMCID: PMC11113218 DOI: 10.1007/s00018-014-1754-5] [Citation(s) in RCA: 146] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2014] [Revised: 09/15/2014] [Accepted: 10/01/2014] [Indexed: 12/13/2022]
Abstract
Small heat-shock proteins (sHsps) are a diverse family of intra-cellular molecular chaperone proteins that play a critical role in mitigating and preventing protein aggregation under stress conditions such as elevated temperature, oxidation and infection. In doing so, they assist in the maintenance of protein homeostasis (proteostasis) thereby avoiding the deleterious effects that result from loss of protein function and/or protein aggregation. The chaperone properties of sHsps are therefore employed extensively in many tissues to prevent the development of diseases associated with protein aggregation. Significant progress has been made of late in understanding the structure and chaperone mechanism of sHsps. In this review, we discuss some of these advances, with a focus on mammalian sHsp hetero-oligomerisation, the mechanism by which sHsps act as molecular chaperones to prevent both amorphous and fibrillar protein aggregation, and the role of post-translational modifications in sHsp chaperone function, particularly in the context of disease.
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Affiliation(s)
- Teresa M Treweek
- Graduate School of Medicine, University of Wollongong, Northfields Avenue, Wollongong, NSW, 2522, Australia.
- Illawarra Health and Medical Research Institute, Northfields Avenue, Wollongong, NSW, 2522, Australia.
| | - Sarah Meehan
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
| | - Heath Ecroyd
- Illawarra Health and Medical Research Institute, Northfields Avenue, Wollongong, NSW, 2522, Australia.
- School of Biological Sciences, University of Wollongong, Northfields Avenue, Wollongong, NSW, 2522, Australia.
| | - John A Carver
- Research School of Chemistry, The Australian National University, Acton, ACT, 2601, Australia.
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Everything but the ACD, Functional Conservation of the Non-conserved Terminal Regions in sHSPs. HEAT SHOCK PROTEINS 2015. [DOI: 10.1007/978-3-319-16077-1_8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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Klein RD, Chidawanyika T, Tims HS, Meulia T, Bouchard RA, Pett VB. Chaperone function of two small heat shock proteins from maize. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2014; 221-222:48-58. [PMID: 24656335 DOI: 10.1016/j.plantsci.2014.01.012] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2013] [Revised: 01/27/2014] [Accepted: 01/29/2014] [Indexed: 05/22/2023]
Abstract
Small heat shock proteins (sHsps) are molecular chaperones that protect cells from the effect of heat and other stresses. Some sHsps are also expressed at specific stages of development. In plants different classes of sHsps are expressed in the various cellular compartments. While the Class I (cytosolic) sHsps in wheat and pea have been studied extensively, there are fewer experimental data on Class II (cytosolic) sHsps, especially in maize. Here we report the expression and purification of two Class II sHsps from Zea mays ssp. mays L. (cv. Oh43). The two proteins have almost identical sequences, with the significant exception of an additional nine-amino-acid intervening sequence near the beginning of the N-terminus in one of them. Both ZmHsp17.0-CII and ZmHsp17.8-CII oligomerize to form dodecamers at temperatures below heat shock, and we were able to visualize these dodecamers with TEM. There are significant differences between the two sHsps during heat shock at 43°C: ZmHsp17.8-CII dissociates into smaller oligomers than ZmHsp17.0-CII, and ZmHsp17.8-CII is a more efficient chaperone with target protein citrate synthase. Together with the previous observation that ZmHsp17.0-CII but not ZmHsp17.8-CII is expressed during development, we propose different roles in the cell for these two sHsps.
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Affiliation(s)
- Roger D Klein
- Department of Chemistry, The College of Wooster, Wooster, OH 44691, USA.
| | | | - Hannah S Tims
- Department of Chemistry, The College of Wooster, Wooster, OH 44691, USA.
| | - Tea Meulia
- Molecular and Cellular Imaging Center, Ohio Agricultural Research and Development Center, Wooster, OH 44691, USA.
| | - Robert A Bouchard
- Horticulture and Crop Science, Ohio Agricultural Research and Development Center, Wooster, OH 44691, USA.
| | - Virginia B Pett
- Department of Chemistry, The College of Wooster, Wooster, OH 44691, USA.
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King AM, Toxopeus J, MacRae TH. Functional differentiation of small heat shock proteins in diapause-destined Artemia embryos. FEBS J 2013; 280:4761-72. [PMID: 23879561 DOI: 10.1111/febs.12442] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2013] [Revised: 07/03/2013] [Accepted: 07/22/2013] [Indexed: 01/01/2023]
Abstract
Encysted embryos of Artemia franciscana cease development and enter diapause, a state of metabolic suppression and enhanced stress tolerance. The development of diapause-destined Artemia embryos is characterized by the coordinated synthesis of the small heat shock proteins (sHsps) p26, ArHsp21 and ArHsp22, with the latter being stress inducible in adults. The amounts of sHsp mRNA and protein varied in Artemia cysts, suggesting transcriptional and translational regulation. By contrast to p26, knockdown of ArHsp21 by RNA interference had no effect on embryo development. ArHsp21 provided limited protection against stressors such as desiccation and freezing but not heat. ArHsp21 may have a non-essential or unidentified role in cysts. Injection of Artemia adults with amounts of ArHsp22 double-stranded RNA less than those used for other sHsps killed females and males, curtailing the analysis of ArHsp22 function in developing embryos and cysts. The results indicate that diapause-destined Artemia embryos synthesize varying amounts of sHsps as a result of differential gene expression and mRNA translation and also suggest that these sHsps have distinctive functions.
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Affiliation(s)
- Allison M King
- Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada
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Quinlan RA, Zhang Y, Lansbury A, Williamson I, Pohl E, Sun F. Changes in the quaternary structure and function of MjHSP16.5 attributable to deletion of the IXI motif and introduction of the substitution, R107G, in the α-crystallin domain. Philos Trans R Soc Lond B Biol Sci 2013; 368:20120327. [PMID: 23530263 PMCID: PMC3638399 DOI: 10.1098/rstb.2012.0327] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The archael small heat-shock protein (sHSP), MjHSP16.5, forms a 24-subunit oligomer with octahedral symmetry. Here, we demonstrate that the IXI motif present in the C-terminal domain is necessary for the oligomerization of MjHSP16.5. Removal increased the in vitro chaperone activity with citrate synthase as the client protein. Less predictable were the effects of the R107G substitution in MjHSP16.5 because of the differences in the oligomerization of metazoan and non-metazoan sHSPs. We present the crystal structure for MjHSP16.5 R107G and compare this with an improved (2.5 Å) crystal structure for wild-type (WT) MjHSP16.5. Although no significant structural differences were found in the crystal, using cryo-electron microscopy, we identified two 24mer species with octahedral symmetry for the WT MjHSP16.5 both at room temperature and at 60°C, all showing two major species with the same diameter of 12.4 nm. Similarly, at room temperature, there are also two kinds of 12.4 nm oligomers for R107G MjHSP16.5, but in the 60°C sample, a larger 24mer species with a diameter of 13.6 nm was observed with significant changes in the fourfold symmetry axis and dimer–dimer interface. This highly conserved arginine, therefore, contributes to the quaternary organization of non-metazoan sHSP oligomers. Potentially, the R107G substitution has functional consequences as R107G MjHSP16.5 was far superior to the WT protein in protecting βL-crystallin against heat-induced aggregation.
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Affiliation(s)
- Roy A Quinlan
- Biophysical Sciences Institute, University of Durham, , South Road, Durham DH1 LE, UK
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Quinlan RA, Ellis RJ. Chaperones: needed for both the good times and the bad times. Philos Trans R Soc Lond B Biol Sci 2013; 368:20130091. [PMID: 23530265 DOI: 10.1098/rstb.2013.0091] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In this issue, we explore the assembly roles of protein chaperones, mainly through the portal of their associated human diseases (e.g. cardiomyopathy, cataract, neurodegeneration, cancer and neuropathy). There is a diversity to chaperone function that goes beyond the current emphasis in the scientific literature on their undoubted roles in protein folding and refolding. The focus on chaperone-mediated protein folding needs to be broadened by the original Laskey discovery that a chaperone assists the assembly of an oligomeric structure, the nucleosome, and the subsequent suggestion by Ellis that other chaperones may function in assembly processes, as well as in folding. There have been a number of recent discoveries that extend this relatively neglected aspect of chaperone biology to include proteostasis, maintenance of the cellular redox potential, genome stability, transcriptional regulation and cytoskeletal dynamics. So central are these processes that we propose that chaperones stand at the crossroads of life and death because they mediate essential functions, not only during the bad times, but also in the good times. We suggest that chaperones facilitate the success of a species, and hence the evolution of individuals within populations, because of their contributions to so many key cellular processes, of which protein folding is only one.
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Affiliation(s)
- Roy A Quinlan
- School of Biological and Biomedical Sciences, University of Durham, South Road, Durham DH1 3LE, UK.
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Fu X, Shi X, Yin L, Liu J, Joo K, Lee J, Chang Z. Small heat shock protein IbpB acts as a robust chaperone in living cells by hierarchically activating its multi-type substrate-binding residues. J Biol Chem 2013; 288:11897-906. [PMID: 23486475 DOI: 10.1074/jbc.m113.450437] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
As ubiquitous molecular chaperones, small heat shock proteins (sHSPs) are crucial for protein homeostasis. It is not clear why sHSPs are able to bind a wide spectrum of non-native substrate proteins and how such binding is enhanced by heat shock. Here, by utilizing a genetically incorporated photo-cross-linker (p-benzoyl-l-phenylalanine), we systematically characterized the substrate-binding residues in IbpB (a sHSP from Escherichia coli) in living cells over a wide spectrum of temperatures (from 20 to 50 °C). A total of 20 and 48 residues were identified at normal and heat shock temperatures, respectively. They are not necessarily hydrophobic and can be classified into three types: types I and II were activated at low and normal temperatures, respectively, and type III mediated oligomerization at low temperature but switched to substrate binding at heat shock temperature. In addition, substrate binding of IbpB in living cells began at temperatures as low as 25 °C and was further enhanced upon temperature elevation. Together, these in vivo data provide novel structural insights into the wide substrate spectrum of sHSPs and suggest that sHSP is able to hierarchically activate its multi-type substrate-binding residues and thus act as a robust chaperone in cells under fluctuating growth conditions.
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Affiliation(s)
- Xinmiao Fu
- From the State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, and Center for Protein Sciences, Peking University, Beijing 100871, China
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