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Hsu HC, Wang J, Kjellgren A, Li H, DeMartino GN. Ηigh-resolution structure of mammalian PI31-20S proteasome complex reveals mechanism of proteasome inhibition. J Biol Chem 2023; 299:104862. [PMID: 37236357 PMCID: PMC10319324 DOI: 10.1016/j.jbc.2023.104862] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2023] [Revised: 05/08/2023] [Accepted: 05/18/2023] [Indexed: 05/28/2023] Open
Abstract
Proteasome-catalyzed protein degradation mediates and regulates critical aspects of many cellular functions and is an important element of proteostasis in health and disease. Proteasome function is determined in part by the types of proteasome holoenzymes formed between the 20S core particle that catalyzes peptide bond hydrolysis and any of multiple regulatory proteins to which it binds. One of these regulators, PI31, was previously identified as an in vitro 20S proteasome inhibitor, but neither the molecular mechanism nor the possible physiologic significance of PI31-mediated proteasome inhibition has been clear. Here we report a high-resolution cryo-EM structure of the mammalian 20S proteasome in complex with PI31. The structure shows that two copies of the intrinsically disordered carboxyl terminus of PI31 are present in the central cavity of the closed-gate conformation of the proteasome and interact with proteasome catalytic sites in a manner that blocks proteolysis of substrates but resists their own degradation. The two inhibitory polypeptide chains appear to originate from PI31 monomers that enter the catalytic chamber from opposite ends of the 20S cylinder. We present evidence that PI31 can inhibit proteasome activity in mammalian cells and may serve regulatory functions for the control of cellular proteostasis.
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Affiliation(s)
- Hao-Chi Hsu
- Department of Structural Biology, Van Andel Institute, Grand Rapids, Michigan, USA
| | - Jason Wang
- Department of Physiology, UT Southwestern Medical Center, Dallas, Texas, USA
| | - Abbey Kjellgren
- Department of Physiology, UT Southwestern Medical Center, Dallas, Texas, USA
| | - Huilin Li
- Department of Structural Biology, Van Andel Institute, Grand Rapids, Michigan, USA.
| | - George N DeMartino
- Department of Physiology, UT Southwestern Medical Center, Dallas, Texas, USA.
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2
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Hsu HC, Wang J, Kjellgren A, Li H, DeMartino GN. High-resolution structure of mammalian PI31â€"20S proteasome complex reveals mechanism of proteasome inhibition. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.04.03.535455. [PMID: 37066326 PMCID: PMC10103979 DOI: 10.1101/2023.04.03.535455] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Proteasome-catalyzed protein degradation mediates and regulates critical aspects of many cellular functions and is an important element of proteostasis in health and disease. Proteasome function is determined in part by the types of proteasome holoenzymes formed between the 20S core particle that catalyzes peptide bond hydrolysis and any of multiple regulatory proteins to which it binds. One of these regulators, PI31, was previously identified as an in vitro 20S proteasome inhibitor, but neither the molecular mechanism nor the possible physiologic significance of PI31-mediated proteasome inhibition has been clear. Here we report a high- resolution cryo-EM structure of the mammalian 20S proteasome in complex with PI31. The structure shows that two copies of the intrinsically-disordered carboxyl-terminus of PI31 are present in the central cavity of the closed-gate conformation of the proteasome and interact with proteasome catalytic sites in a manner that blocks proteolysis of substrates but resists their own degradation. The two inhibitory polypeptide chains appear to originate from PI31 monomers that enter the catalytic chamber from opposite ends of the 20S cylinder. We present evidence that PI31 can inhibit proteasome activity in mammalian cells and may serve regulatory functions for the control of cellular proteostasis.
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3
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Fang R, Hon J, Zhou M, Lu Y. An empirical energy landscape reveals mechanism of proteasome in polypeptide translocation. eLife 2022; 11:71911. [PMID: 35050852 PMCID: PMC8853663 DOI: 10.7554/elife.71911] [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: 07/03/2021] [Accepted: 01/17/2022] [Indexed: 11/15/2022] Open
Abstract
The ring-like ATPase complexes in the AAA+ family perform diverse cellular functions that require coordination between the conformational transitions of their individual ATPase subunits (Erzberger and Berger, 2006; Puchades et al., 2020). How the energy from ATP hydrolysis is captured to perform mechanical work by these coordinated movements is unknown. In this study, we developed a novel approach for delineating the nucleotide-dependent free-energy landscape (FEL) of the proteasome’s heterohexameric ATPase complex based on complementary structural and kinetic measurements. We used the FEL to simulate the dynamics of the proteasome and quantitatively evaluated the predicted structural and kinetic properties. The FEL model predictions are consistent with a wide range of experimental observations in this and previous studies and suggested novel mechanistic features of the proteasomal ATPases. We find that the cooperative movements of the ATPase subunits result from the design of the ATPase hexamer entailing a unique free-energy minimum for each nucleotide-binding status. ATP hydrolysis dictates the direction of substrate translocation by triggering an energy-dissipating conformational transition of the ATPase complex. In cells, many biological processes are carried out by large complexes made up of different proteins. These macromolecules act like miniature machines, flexing and moving their various parts to perform their cellular roles. One such complex is the 26S proteasome, which is responsible for recycling other proteins in the cell. The proteasome consists of approximately 31 subunits, including a ring of six ATPase enzymes that provide the complex with the energy it needs to mechanically unfold proteins. To understand how the proteasome and other large complexes work, researchers need to be able to monitor how their structure changes over time. These dynamics are challenging to probe directly with experiments, but can be assessed using computer simulations which track the movement of individual molecules and atoms. However, currently available computer systems do not have enough power to simulate the dynamics of large protein assemblies, like the 26S proteasome: for example, it would take longer than a thousand years to model how each atom in the complex moves over a timescale in which a biological change would happen (roughly 100ms). Here, Fang, Hon et al. have developed a new approach to simulate the structural dynamics of the proteasome’s ring of ATPase enzymes. Different known structures of the proteasome were used to identify the range of possible movements and shapes the complex can make. Fang, Hon et al. then used this data to calculate the energy level of each structure – also known as the ‘free energy landscape’ – and the rate of transition between them. This made it possible to simulate how the different ATPase enzymes move within the ring under a wide range of conditions. The simulated ATPase movements predicted how the proteasome machine would behave during various tasks, including degrading other proteins. Fan, Hon et al. carefully examined these predictions and found that they were consistent with experimental observations, validating their new simulation method. This work demonstrates the feasibility of simulating the actions of a large protein complex based on its free energy landscape. The results offer important insights into the functional mechanics of the 26S proteasome and related protein machines. Further work may help to simplify this process so the approach can be used to investigate the dynamics of other protein assemblies.
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Affiliation(s)
- Rui Fang
- Department of Systems Biology, Harvard Medical School, Boston, United States
| | - Jason Hon
- Department of Systems Biology, Harvard Medical School, Boston, United States
| | - Mengying Zhou
- Department of Systems Biology, Harvard Medical School, Boston, United States
| | - Ying Lu
- Department of Systems Biology, Harvard Medical School, Boston, United States
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4
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Association with proteasome determines pathogenic threshold of polyglutamine expansion diseases. Biochem Biophys Res Commun 2020; 536:95-99. [PMID: 33370719 DOI: 10.1016/j.bbrc.2020.12.065] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Accepted: 12/18/2020] [Indexed: 11/21/2022]
Abstract
Expansion of glutamine residue track (polyQ) within soluble protein is responsible for eight autosomal-dominant genetic neurodegenerative disorders. These disorders affect cerebellum, striatum, basal ganglia and other brain regions. Each disease develops when polyQ expansion exceeds a pathogenic threshold (Qth). A pathogenic threshold is unique for each disease but the reasons for variability in Qth within this family of proteins are poorly understood. In the previous publication we proposed that polarity of the regions flanking polyQ track in each protein plays a key role in defining Qth value [1]. To explain the correlation between the polarity of the flanking sequences and Qth we performed quantitative analysis of interactions between polyQ-expanded proteins and proteasome. Based on structural and theoretical modeling, we predict that Qth value is determined by the energy of polar interaction of the flanking regions with the polyQ and proteasome. More polar flanking regions facilitate unfolding of α-helical polyQ conformation adopted inside the proteasome and as a result, increase Qth. Predictions of our model are consistent with Qth values observed in clinic for each of the eight polyQ-expansion disorders. Our results suggest that the agents that can destabilize polyQ α-helical structure may have a beneficial therapeutic effect for treatment of polyQ-expansion disorders.
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5
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An Allosteric Interaction Network Promotes Conformation State-Dependent Eviction of the Nas6 Assembly Chaperone from Nascent 26S Proteasomes. Cell Rep 2020; 26:483-495.e5. [PMID: 30625330 PMCID: PMC6344052 DOI: 10.1016/j.celrep.2018.12.042] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2018] [Revised: 11/15/2018] [Accepted: 12/11/2018] [Indexed: 12/04/2022] Open
Abstract
The 26S proteasome is the central ATP-dependent protease in eukaryotes and is essential for organismal health. Proteasome assembly is mediated by several dedicated, evolutionarily conserved chaperone proteins. These chaperones associate transiently with assembly intermediates but are absent from mature proteasomes. Chaperone eviction upon completion of proteasome assembly is necessary for normal proteasome function, but how they are released remains unresolved. Here, we demonstrate that the Nas6 assembly chaperone, homolog of the human oncogene gankyrin, is evicted from nascent proteasomes during completion of assembly via a conformation-specific allosteric interaction of the Rpn5 subunit with the proteasomal ATPase ring. Subsequent ATP binding by the ATPase subunit Rpt3 promotes conformational remodeling of the ATPase ring that evicts Nas6 from the nascent proteasome. Our study demonstrates how assembly-coupled allosteric signals promote chaperone eviction and provides a framework for understanding the eviction of other chaperones from this bio-medically important molecular machine. Nemec et al. report how the evolutionarily conserved Nas6 assembly chaperone is evicted from nascent 26S proteasomes. Nucleotide binding events within the nascent proteasome trigger formation of conformation-specific intersubunit contacts that expel Nas6. This mechanism may serve a quality control function by blocking formation of 26S proteasomes from defective components.
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6
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Eisele MR, Reed RG, Rudack T, Schweitzer A, Beck F, Nagy I, Pfeifer G, Plitzko JM, Baumeister W, Tomko RJ, Sakata E. Expanded Coverage of the 26S Proteasome Conformational Landscape Reveals Mechanisms of Peptidase Gating. Cell Rep 2019; 24:1301-1315.e5. [PMID: 30067984 PMCID: PMC6140342 DOI: 10.1016/j.celrep.2018.07.004] [Citation(s) in RCA: 86] [Impact Index Per Article: 17.2] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Revised: 06/08/2018] [Accepted: 07/02/2018] [Indexed: 12/31/2022] Open
Abstract
The proteasome is the central protease for intracellular protein breakdown. Coordinated binding and hydrolysis of ATP by the six proteasomal ATPase subunits induces conformational changes that drive the unfolding and translocation of substrates into the proteolytic 20S core particle for degradation. Here, we combine genetic and biochemical approaches with cryo-electron microscopy and integrative modeling to dissect the relationship between individual nucleotide binding events and proteasome conformational dynamics. We demonstrate unique impacts of ATP binding by individual ATPases on the proteasome conformational distribution and report two conformational states of the proteasome suggestive of a rotary ATP hydrolysis mechanism. These structures, coupled with functional analyses, reveal key roles for the ATPases Rpt1 and Rpt6 in gating substrate entry into the core particle. This deepened knowledge of proteasome conformational dynamics reveals key elements of intersubunit communication within the proteasome and clarifies the regulation of substrate entry into the proteolytic chamber.
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Affiliation(s)
- Markus R Eisele
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Randi G Reed
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, FL 32306-4300, USA
| | - Till Rudack
- Department of Biophysics, Ruhr University Bochum, 44801 Bochum, Germany
| | - Andreas Schweitzer
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Florian Beck
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Istvan Nagy
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Günter Pfeifer
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Jürgen M Plitzko
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Wolfgang Baumeister
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.
| | - Robert J Tomko
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, FL 32306-4300, USA.
| | - Eri Sakata
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.
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7
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Sitaraman S, Na CL, Yang L, Filuta A, Bridges JP, Weaver TE. Proteasome dysfunction in alveolar type 2 epithelial cells is associated with acute respiratory distress syndrome. Sci Rep 2019; 9:12509. [PMID: 31467330 PMCID: PMC6715642 DOI: 10.1038/s41598-019-49020-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2019] [Accepted: 08/19/2019] [Indexed: 01/06/2023] Open
Abstract
Proteasomes are a critical component of quality control that regulate turnover of short-lived, unfolded, and misfolded proteins. Proteasome activity has been therapeutically targeted and considered as a treatment option for several chronic lung disorders including pulmonary fibrosis. Although pharmacologic inhibition of proteasome activity effectively prevents the transformation of fibroblasts to myofibroblasts, the effect on alveolar type 2 (AT2) epithelial cells is not clear. To address this knowledge gap, we generated a genetic model in which a proteasome subunit, RPT3, which promotes assembly of active 26S proteasome, was conditionally deleted in AT2 cells of mice. Partial deletion of RPT3 resulted in 26S proteasome dysfunction, leading to augmented cell stress and cell death. Acute loss of AT2 cells resulted in depletion of alveolar surfactant, disruption of the alveolar epithelial barrier and, ultimately, lethal acute respiratory distress syndrome (ARDS). This study underscores importance of proteasome function in maintenance of AT2 cell homeostasis and supports the need to further investigate the role of proteasome dysfunction in ARDS pathogenesis.
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Affiliation(s)
- Sneha Sitaraman
- Division of Pulmonary Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, 45229, USA
| | - Cheng-Lun Na
- Division of Pulmonary Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, 45229, USA
| | - Li Yang
- Division of Pulmonary Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, 45229, USA
| | - Alyssa Filuta
- Division of Pulmonary Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, 45229, USA
| | - James P Bridges
- Division of Pulmonary, Critical Care and Sleep Medicine, National Jewish Health, Denver, Colorado, 80206, USA
| | - Timothy E Weaver
- Division of Pulmonary Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, 45229, USA.
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8
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Kors S, Geijtenbeek K, Reits E, Schipper-Krom S. Regulation of Proteasome Activity by (Post-)transcriptional Mechanisms. Front Mol Biosci 2019; 6:48. [PMID: 31380390 PMCID: PMC6646590 DOI: 10.3389/fmolb.2019.00048] [Citation(s) in RCA: 62] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2019] [Accepted: 06/11/2019] [Indexed: 12/23/2022] Open
Abstract
Intracellular protein synthesis, folding, and degradation are tightly controlled processes to ensure proper protein homeostasis. The proteasome is responsible for the degradation of the majority of intracellular proteins, which are often targeted for degradation via polyubiquitination. However, the degradation rate of proteins is also affected by the capacity of proteasomes to recognize and degrade these substrate proteins. This capacity is regulated by a variety of proteasome modulations including (1) changes in complex composition, (2) post-translational modifications, and (3) altered transcription of proteasomal subunits and activators. Various diseases are linked to proteasome modulation and altered proteasome function. A better understanding of these modulations may offer new perspectives for therapeutic intervention. Here we present an overview of these three proteasome modulating mechanisms to give better insight into the diversity of proteasomes.
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Affiliation(s)
- Suzan Kors
- Department of Medical Biology, Amsterdam UMC, University of Amsterdam, Amsterdam, Netherlands
| | - Karlijne Geijtenbeek
- Department of Medical Biology, Amsterdam UMC, University of Amsterdam, Amsterdam, Netherlands
| | - Eric Reits
- Department of Medical Biology, Amsterdam UMC, University of Amsterdam, Amsterdam, Netherlands
| | - Sabine Schipper-Krom
- Department of Medical Biology, Amsterdam UMC, University of Amsterdam, Amsterdam, Netherlands
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9
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Ma RR, Sun J, Fang WH, Dong YP, Ruan JM, Yang XL, Hu K. Identification of Carassius auratus gibelio liver cell proteins interacting with the GABA A receptor γ2 subunit using a yeast two-hybrid system. FISH PHYSIOLOGY AND BIOCHEMISTRY 2019; 45:199-208. [PMID: 30242696 DOI: 10.1007/s10695-018-0554-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/02/2018] [Accepted: 08/14/2018] [Indexed: 06/08/2023]
Abstract
The γ-aminobutyric acid type A (GABAA) receptor is an important pentameric inhibitory neurotransmitter receptor, and the γ2 subunit of this receptor plays a key role in potentiation of the GABAA response. We previously detected that the expression of GABAA receptor in the livers of Carassius auratus gibelio significantly increased after medication (avermectin and difloxacin treatment). In order to better understand the mechanism of action of the GABAA receptor γ2 subunit in the livers of C. auratus gibelio, we constructed a C. auratus gibelio liver cDNA library (the titer value of 1.2 × 106 cfu/mL) and identified the proteins that interact with the GABAA receptor γ2 subunit by using a yeast two-hybrid assay. The yeast two-hybrid screening yielded seven positive clones, namely, prelid3b, cdc42, sgk1, spg21, proteasome, chia.5, and AP-3 complex subunit beta-1, all of which have been annotated by the NCBI database. The functions of these proteins are complex; therefore, additional studies are required to determine the specific interactions of these proteins with the GABAA receptor γ2 subunit in the liver of C. auratus gibelio. Although the interactions identified by the yeast two-hybrid system should be considered as preliminary results, the findings of this study may provide further direction and a foundation for future research focusing on the mechanisms of the GABAA receptor γ2 subunit in C. auratus gibelio livers.
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Affiliation(s)
- Rong-Rong Ma
- National Pathogen Collection Center for Aquatic Animals, Shanghai Ocean University, Shanghai, China
- Shanghai Collaborative Innovation for Aquatic Animal Genetics and Breeding, Shanghai Ocean University, Shanghai, China
- National Demonstration Center for Experimental Fisheries Science Education, Shanghai Ocean University, Shanghai, China
- Key Laboratory of Fisheries Ecology of the Yangtze Estuary, East China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Shanghai, China
| | - Jing Sun
- National Pathogen Collection Center for Aquatic Animals, Shanghai Ocean University, Shanghai, China
- Shanghai Collaborative Innovation for Aquatic Animal Genetics and Breeding, Shanghai Ocean University, Shanghai, China
- National Demonstration Center for Experimental Fisheries Science Education, Shanghai Ocean University, Shanghai, China
| | - Wen-Hong Fang
- Key Laboratory of Fisheries Ecology of the Yangtze Estuary, East China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Shanghai, China
| | - Ya-Ping Dong
- National Pathogen Collection Center for Aquatic Animals, Shanghai Ocean University, Shanghai, China
- Shanghai Collaborative Innovation for Aquatic Animal Genetics and Breeding, Shanghai Ocean University, Shanghai, China
- National Demonstration Center for Experimental Fisheries Science Education, Shanghai Ocean University, Shanghai, China
| | - Ji-Ming Ruan
- College of Animal Sciences and Technology, Jiangxi Agricultural University, Nanchang, Jiangxi, China
| | - Xian-Le Yang
- National Pathogen Collection Center for Aquatic Animals, Shanghai Ocean University, Shanghai, China
- Shanghai Collaborative Innovation for Aquatic Animal Genetics and Breeding, Shanghai Ocean University, Shanghai, China
- National Demonstration Center for Experimental Fisheries Science Education, Shanghai Ocean University, Shanghai, China
| | - Kun Hu
- National Pathogen Collection Center for Aquatic Animals, Shanghai Ocean University, Shanghai, China.
- Shanghai Collaborative Innovation for Aquatic Animal Genetics and Breeding, Shanghai Ocean University, Shanghai, China.
- National Demonstration Center for Experimental Fisheries Science Education, Shanghai Ocean University, Shanghai, China.
- College of Fisheries and Life Science, Shanghai Ocean University, 999 Hucheng Huan Road, Lingang New City Shanghai, 201306, China.
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10
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de la Peña AH, Goodall EA, Gates SN, Lander GC, Martin A. Substrate-engaged 26 S proteasome structures reveal mechanisms for ATP-hydrolysis-driven translocation. Science 2018; 362:science.aav0725. [PMID: 30309908 DOI: 10.1126/science.aav0725] [Citation(s) in RCA: 196] [Impact Index Per Article: 32.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2018] [Accepted: 10/04/2018] [Indexed: 01/03/2023]
Abstract
The 26S proteasome is the primary eukaryotic degradation machine and thus is critically involved in numerous cellular processes. The heterohexameric adenosine triphosphatase (ATPase) motor of the proteasome unfolds and translocates targeted protein substrates into the open gate of a proteolytic core while a proteasomal deubiquitinase concomitantly removes substrate-attached ubiquitin chains. However, the mechanisms by which ATP hydrolysis drives the conformational changes responsible for these processes have remained elusive. Here we present the cryo-electron microscopy structures of four distinct conformational states of the actively ATP-hydrolyzing, substrate-engaged 26S proteasome. These structures reveal how mechanical substrate translocation accelerates deubiquitination and how ATP-binding, -hydrolysis, and phosphate-release events are coordinated within the AAA+ (ATPases associated with diverse cellular activities) motor to induce conformational changes and propel the substrate through the central pore.
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Affiliation(s)
- Andres H de la Peña
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, CA 92037, USA
| | - Ellen A Goodall
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA.,California Institute for Quantitative Biosciences, University of California at Berkeley, Berkeley, CA 94720, USA
| | - Stephanie N Gates
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA.,California Institute for Quantitative Biosciences, University of California at Berkeley, Berkeley, CA 94720, USA.,Howard Hughes Medical Institute, University of California at Berkeley, Berkeley, CA 94720, USA
| | - Gabriel C Lander
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, CA 92037, USA.
| | - Andreas Martin
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA. .,California Institute for Quantitative Biosciences, University of California at Berkeley, Berkeley, CA 94720, USA.,Howard Hughes Medical Institute, University of California at Berkeley, Berkeley, CA 94720, USA
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11
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Lee D, Takayama S, Goldberg AL. ZFAND5/ZNF216 is an activator of the 26S proteasome that stimulates overall protein degradation. Proc Natl Acad Sci U S A 2018; 115:E9550-E9559. [PMID: 30254168 PMCID: PMC6187164 DOI: 10.1073/pnas.1809934115] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
ZFAND5/ZNF216, a member of the zinc finger AN1-type domain family, is abundant in heart and brain, but is induced in skeletal muscle during atrophy (although not in proteotoxic stress). Because mice lacking ZFAND5 exhibit decreased atrophy, a role in stimulating protein breakdown seemed likely. Addition of recombinant ZFAND5 to purified 26S proteasomes stimulated hydrolysis of ubiquitinated proteins, short peptides, and ATP. Mutating its C-terminal AN1 domain abolished the stimulation of proteasomal peptidase activity. Mutating its N-terminal zinc finger A20 domain, which binds ubiquitin chains, prevented the enhanced degradation of ubiquitinated proteins without affecting peptidase activity. Mouse embryonic fibroblast (MEF) cells lacking ZFAND5 had lower rates of protein degradation and proteasomal activity than WT MEFs. ZFAND5 addition to cell lysates stimulated proteasomal activity and protein degradation. Unlike other proteasome regulators, ZFAND5 enhances multiple 26S activities and overall cellular protein breakdown.
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Affiliation(s)
- Donghoon Lee
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115
| | | | - Alfred L Goldberg
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115;
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12
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Liu Y, Qiao F, Leiferman PC, Ross A, Schlenker EH, Wang H. FOXOs modulate proteasome activity in human-induced pluripotent stem cells of Huntington's disease and their derived neural cells. Hum Mol Genet 2018; 26:4416-4428. [PMID: 28973411 PMCID: PMC6075623 DOI: 10.1093/hmg/ddx327] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2017] [Accepted: 08/17/2017] [Indexed: 12/27/2022] Open
Abstract
Although it has been speculated that proteasome dysfunction may contribute to the pathogenesis of Huntington's disease (HD), a devastating neurodegenerative disorder, how proteasome activity is regulated in HD affected stem cells and somatic cells remains largely unclear. To better understand the pathogenesis of HD, we analyzed proteasome activity and the expression of FOXO transcription factors in three wild-type (WT) and three HD induced-pluripotent stem cell (iPSC) lines. HD iPSCs exhibited elevated proteasome activity and higher levels of FOXO1 and FOXO4 proteins. Knockdown of FOXO4 but not FOXO1 expression decreased proteasome activity. Following neural differentiation, the HD-iPSC-derived neural progenitor cells (NPCs) demonstrated lower levels of proteasome activity and FOXO expressions than their WT counterparts. More importantly, overexpression of FOXO4 but not FOXO1 in HD NPCs dramatically enhanced proteasome activity. When HD NPCs were further differentiated into DARPP32-positive neurons, these HD neurons were more susceptible to death than WT neurons and formed Htt aggregates under the condition of oxidative stress. Similar to HD NPCs, HD-iPSC-derived neurons showed reduced proteasome activity and diminished FOXO4 expression compared to WT-iPSC-derived neurons. Furthermore, HD iPSCs had lower AKT activities than WT iPSCs, whereas the neurons derived from HD iPSC had higher AKT activities than their WT counterparts. Inhibiting AKT activity increased both FOXO4 level and proteasome activity, indicating a potential role of AKT in regulating FOXO levels. These data suggest that FOXOs modulate proteasome activity, and thus represents a potentially valuable therapeutic target for HD.
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Affiliation(s)
- Yanying Liu
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069, USA
| | - Fangfang Qiao
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069, USA
| | | | - Alan Ross
- Sanford Medical Genetics Laboratory, Sioux Falls, SD 57105, USA
| | - Evelyn H Schlenker
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069, USA
| | - Hongmin Wang
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069, USA
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13
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Sun S, Liu S, Zhang Z, Zeng W, Sun C, Tao T, Lin X, Feng XH. Phosphatase UBLCP1 controls proteasome assembly. Open Biol 2018; 7:rsob.170042. [PMID: 28539385 PMCID: PMC5451543 DOI: 10.1098/rsob.170042] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Accepted: 04/20/2017] [Indexed: 12/26/2022] Open
Abstract
Ubiquitin-like domain-containing C-terminal domain phosphatase 1 (UBLCP1), an FCP/SCP phosphatase family member, was identified as the first proteasome phosphatase. UBLCP1 binds to proteasome subunit Rpn1 and dephosphorylates the proteasome in vitro. However, it is still unclear which proteasome subunit(s) are the bona fide substrate(s) of UBLCP1 and the precise mechanism for proteasome regulation remains elusive. Here, we show that UBLCP1 selectively binds to the 19S regulatory particle (RP) through its interaction with Rpn1, but not the 20S core particle (CP) or the 26S proteasome holoenzyme. In the RP, UBLCP1 dephosphorylates the subunit Rpt1, impairs its ATPase activity, and consequently disrupts the 26S proteasome assembly, yet it has no effects on the RP assembly from precursor complexes. The Rpn1-binding and phosphatase activities of UBLCP1 are essential for its function on Rpt1 dephosphorylation and proteasome activity both in vivo and in vitro. Our study establishes the essential role of the UBLCP1/Rpn1/Rpt1 complex in regulating proteasome assembly.
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Affiliation(s)
- Shuangwu Sun
- Life Sciences Institute and Innovation Center for Cell Signaling Network, Zhejiang University, Hangzhou, Zhejiang, People's Republic of China
| | - Sisi Liu
- Life Sciences Institute and Innovation Center for Cell Signaling Network, Zhejiang University, Hangzhou, Zhejiang, People's Republic of China
| | - Zhengmao Zhang
- Michael E. DeBakey, Department of Surgery, Houston, TX, USA.,Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
| | - Wang Zeng
- Life Sciences Institute and Innovation Center for Cell Signaling Network, Zhejiang University, Hangzhou, Zhejiang, People's Republic of China
| | - Chuang Sun
- Michael E. DeBakey, Department of Surgery, Houston, TX, USA
| | - Tao Tao
- State Key Laboratory of Stress Cell Biology, School of Life Sciences, Xiamen University, Xiamen, Fujian, People's Republic of China
| | - Xia Lin
- Michael E. DeBakey, Department of Surgery, Houston, TX, USA.,Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
| | - Xin-Hua Feng
- Life Sciences Institute and Innovation Center for Cell Signaling Network, Zhejiang University, Hangzhou, Zhejiang, People's Republic of China .,Michael E. DeBakey, Department of Surgery, Houston, TX, USA.,Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
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14
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Marquez-Lona EM, Torres-Machorro AL, Gonzales FR, Pillus L, Patrick GN. Phosphorylation of the 19S regulatory particle ATPase subunit, Rpt6, modifies susceptibility to proteotoxic stress and protein aggregation. PLoS One 2017; 12:e0179893. [PMID: 28662109 PMCID: PMC5491056 DOI: 10.1371/journal.pone.0179893] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2016] [Accepted: 06/06/2017] [Indexed: 12/22/2022] Open
Abstract
The ubiquitin proteasome system (UPS) is a highly conserved and tightly regulated biochemical pathway that degrades the majority of proteins in eukaryotic cells. Importantly, the UPS is responsible for counteracting altered protein homeostasis induced by a variety of proteotoxic stresses. We previously reported that Rpt6, the ATPase subunit of the 19S regulatory particle (RP) of the 26S proteasome, is phosphorylated in mammalian neurons at serine 120 in response to neuronal activity. Furthermore, we found that Rpt6 S120 phosphorylation, which regulates the activity and distribution of proteasomes in neurons, is relevant for proteasome-dependent synaptic remodeling and function. To better understand the role of proteasome phosphorylation, we have constructed models of altered Rpt6 phosphorylation in S. cerevisiae by introducing chromosomal point mutations that prevent or mimic phosphorylation at the conserved serine (S119). We find that mutants which prevent Rpt6 phosphorylation at this site (rpt6-S119A), had increased susceptibility to proteotoxic stress, displayed abnormal morphology and had reduced proteasome activity. Since impaired proteasome function has been linked to the aggregation of toxic proteins including the Huntington’s disease (HD) related huntingtin (Htt) protein with expanded polyglutamine repeats, we evaluated the extent of Htt aggregation in our phospho-dead (rpt6-S119A) and phospho-mimetic (rpt6-S119D) mutants. We showed Htt103Q aggregate size to be significantly larger in rpt6-S119A mutants compared to wild-type or rpt6-S119D strains. Furthermore, we observed that phosphorylation of endogenous Rpt6 at S119 is increased in response to various stress conditions. Together, these data suggest that Rpt6 phosphorylation at S119 may play an important function in proteasome-dependent relief of proteotoxic stress that can be critical in protein aggregation pathologies.
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Affiliation(s)
- Esther Magdalena Marquez-Lona
- Section of Neurobiology, Division of Biological Sciences, University of California San Diego, La Jolla, California, United States of America
| | - Ana Lilia Torres-Machorro
- Section of Molecular Biology and UCSD Moores Cancer Center, Division of Biological Sciences, University of California San Diego, La Jolla, California, United States of America
| | - Frankie R. Gonzales
- Section of Neurobiology, Division of Biological Sciences, University of California San Diego, La Jolla, California, United States of America
| | - Lorraine Pillus
- Section of Molecular Biology and UCSD Moores Cancer Center, Division of Biological Sciences, University of California San Diego, La Jolla, California, United States of America
| | - Gentry N. Patrick
- Section of Neurobiology, Division of Biological Sciences, University of California San Diego, La Jolla, California, United States of America
- * E-mail:
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15
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Mayor T, Sharon M, Glickman MH. Tuning the proteasome to brighten the end of the journey. Am J Physiol Cell Physiol 2016; 311:C793-C804. [PMID: 27605452 DOI: 10.1152/ajpcell.00198.2016] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2016] [Accepted: 09/04/2016] [Indexed: 02/07/2023]
Abstract
Degradation by the proteasome is the fate for a large portion of cellular proteins, and it plays a major role in maintaining protein homeostasis, as well as in regulating many cellular processes like cell cycle progression. A decrease in proteasome activity has been linked to aging and several age-related neurodegenerative pathologies and highlights the importance of the ubiquitin proteasome system regulation. While the proteasome has been traditionally viewed as a constitutive element of proteolysis, major studies have highlighted how different regulatory mechanisms can impact its activity. Importantly, alterations of proteasomal activity may have major impacts for its function and in therapeutics. On one hand, increasing proteasome activity could be beneficial to prevent the age-related downfall of protein homeostasis, whereas inhibiting or reducing its activity can prevent the proliferation of cancer cells.
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Affiliation(s)
- Thibault Mayor
- Department of Biochemistry and Molecular Biology, Michael Smith Laboratories, University of British Columbia, Vancouver, Canada;
| | - Michal Sharon
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel; and
| | - Michael H Glickman
- Department of Biology, Technion-Israel Institute of Technology, Haifa, Israel
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16
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Caputi FF, Carboni L, Mazza D, Candeletti S, Romualdi P. Cocaine and ethanol target 26S proteasome activity and gene expression in neuroblastoma cells. Drug Alcohol Depend 2016; 161:265-75. [PMID: 26922280 DOI: 10.1016/j.drugalcdep.2016.02.012] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Revised: 01/26/2016] [Accepted: 02/05/2016] [Indexed: 10/22/2022]
Abstract
BACKGROUND Ethanol and cocaine are widely abused drugs triggering long-lasting changes in neuronal circuits and synaptic transmission through the regulation of enzyme activity and gene expression. Compelling evidence indicates that the ubiquitin-proteasome system plays a role in the molecular changes induced by addictive substances, impacting on several mechanisms implicated in abuse. The goal of these studies was to evaluate the effects of cocaine or ethanol on proteasome activity in neuroblastoma cells. Moreover, the gene expression of specific subunits was assessed. METHODS Chymotrypsin-like activity was measured after 2 h, 24 h, and 48 h exposure to 5 μM cocaine or 40 mM ethanol. Proteasome subunit transcripts were evaluated by qPCR at the same time-points. RESULTS Treatments modified proteasome function in opposite directions, since cocaine increased and ethanol reduced chymotrypsin-like activity. Interestingly, we observed gene expression alterations induced by these drugs. In the core particle, the β1 and α5 subunits were mainly up-regulated by cocaine, whereas α6 transcripts were mostly decreased. β2 and β5 did not change. Similarly, ethanol exposure generally increased β1 and α5 mRNAs. Moreover, the β2 subunit was significantly up-regulated by ethanol only. The β5 and α6 subunits were not altered. In the regulatory particle, Rpt3 was increased by cocaine exposure, whereas it was reduced by ethanol. No significant Rpn9 alterations were observed. CONCLUSIONS These findings support the notion that addictive substances regulate proteasome function, contributing to the dysregulations related to drug abuse since the availability of adequate subunit amounts is necessary for proper complex assembly and function.
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Affiliation(s)
- Francesca Felicia Caputi
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum-University of Bologna, Irnerio 48, 40126 Bologna, Italy.
| | - Lucia Carboni
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum-University of Bologna, Irnerio 48, 40126 Bologna, Italy
| | - Daria Mazza
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum-University of Bologna, Irnerio 48, 40126 Bologna, Italy
| | - Sanzio Candeletti
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum-University of Bologna, Irnerio 48, 40126 Bologna, Italy
| | - Patrizia Romualdi
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum-University of Bologna, Irnerio 48, 40126 Bologna, Italy
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17
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Kim YC, Snoberger A, Schupp J, Smith DM. ATP binding to neighbouring subunits and intersubunit allosteric coupling underlie proteasomal ATPase function. Nat Commun 2015; 6:8520. [PMID: 26465836 PMCID: PMC4608255 DOI: 10.1038/ncomms9520] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2015] [Accepted: 08/30/2015] [Indexed: 12/31/2022] Open
Abstract
The primary functions of the proteasome are driven by a highly allosteric ATPase complex. ATP binding to only two subunits in this hexameric complex triggers substrate binding, ATPase–20S association and 20S gate opening. However, it is unclear how ATP binding and hydrolysis spatially and temporally coordinates these allosteric effects to drive substrate translocation into the 20S. Here, we use FRET to show that the proteasomal ATPases from eukaryotes (RPTs) and archaea (PAN) bind ATP with high affinity at neighbouring subunits, which complements the well-established spiral-staircase topology of the 26S ATPases. We further show that two conserved arginine fingers in PAN located at the subunit interface work together as a single allosteric unit to mediate the allosteric effects of ATP binding, without altering the nucleotide-binding pattern. Rapid kinetics analysis also shows that ring resetting of a sequential hydrolysis mechanism can be explained by thermodynamic equilibrium binding of ATP. These data support a model whereby these two functionally distinct allosteric networks cooperate to translocate polypeptides into the 20S for degradation. The 26S proteasome contains a hexamer of ATPase subunits, which binds, unfolds and translocates substrates in an ATP-dependent manner. Kim et al. use FRET to show that ATP binding preferentially occurs at neighbouring subunits of the hexamer, and identify two allosteric systems that coordinate translocation.
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Affiliation(s)
- Young-Chan Kim
- Department of Biochemistry, West Virginia University, 1 Medical Center Drive, Morgantown, West Virginia 26506, USA
| | - Aaron Snoberger
- Department of Biochemistry, West Virginia University, 1 Medical Center Drive, Morgantown, West Virginia 26506, USA
| | - Jane Schupp
- Department of Biochemistry, West Virginia University, 1 Medical Center Drive, Morgantown, West Virginia 26506, USA
| | - David M Smith
- Department of Biochemistry, West Virginia University, 1 Medical Center Drive, Morgantown, West Virginia 26506, USA
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18
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Proteasome Activation is Mediated via a Functional Switch of the Rpt6 C-terminal Tail Following Chaperone-dependent Assembly. Sci Rep 2015; 5:14909. [PMID: 26449534 PMCID: PMC4598862 DOI: 10.1038/srep14909] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2015] [Accepted: 09/11/2015] [Indexed: 11/18/2022] Open
Abstract
In the proteasome, the proteolytic 20S core particle (CP) associates with the 19S regulatory particle (RP) to degrade polyubiquitinated proteins. Six ATPases (Rpt1-Rpt6) of the RP form a hexameric Rpt ring and interact with the heptameric α ring (α1–α7) of the CP via the Rpt C-terminal tails individually binding to the α subunits. Importantly, the Rpt6 tail has been suggested to be crucial for RP assembly. Here, we show that the interaction of the CP and Rpt6 tail promotes a CP-Rpt3 tail interaction, and that they jointly mediate proteasome activation via opening the CP gate for substrate entry. The Rpt6 tail forms a novel relationship with the Nas6 chaperone, which binds to Rpt3 and regulates the CP-Rpt3 tail interaction, critically influencing cell growth and turnover of polyubiquitinated proteins. CP-Rpt6 tail binding promotes the release of Nas6 from the proteasome. Based on disulfide crosslinking that detects cognate α3-Rpt6 tail and α2-Rpt3 tail interactions in the proteasome, decreased α3-Rpt6 tail interaction facilitates robust α2-Rpt3 tail interaction that is also strongly ATP-dependent. Together, our data support the reported role of Rpt6 during proteasome assembly, and suggest that its function switches from anchoring for RP assembly into promoting Rpt3-dependent activation of the mature proteasome.
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19
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Proteasome inhibitors induce AMPK activation via CaMKKβ in human breast cancer cells. Breast Cancer Res Treat 2015; 153:79-88. [DOI: 10.1007/s10549-015-3512-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2015] [Accepted: 07/18/2015] [Indexed: 01/15/2023]
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20
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Inobe T, Genmei R. N-Terminal Coiled-Coil Structure of ATPase Subunits of 26S Proteasome Is Crucial for Proteasome Function. PLoS One 2015. [PMID: 26208326 PMCID: PMC4514846 DOI: 10.1371/journal.pone.0134056] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The proteasome is an essential proteolytic machine in eukaryotic cells, where it removes damaged proteins and regulates many cellular activities by degrading ubiquitinated proteins. Its heterohexameric AAA+ ATPase Rpt subunits play a central role in proteasome activity by the engagement of substrate unfolding and translocation for degradation; however, its detailed mechanism remains poorly understood. In contrast to AAA+ ATPase domains, their N-terminal regions of Rpt subunits substantially differ from each other. Here, to investigate the requirements and roles of the N-terminal regions of six Rpt subunits derived from Saccharomyces cerevisiae, we performed systematic mutational analysis using conditional knockdown yeast strains for each Rpt subunit and bacterial heterologous expression system of the base subcomplex. We showed that the formation of the coiled-coil structure was the most important for the N-terminal region of Rpt subunits. The primary role of coiled-coil structure would be the maintenance of the ring structure with the defined order. However, the coiled-coil region would be also be involved in substrate recognition and an interaction between lid and base subcomplexes.
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Affiliation(s)
- Tomonao Inobe
- Frontier Research Core for Life Sciences, University of Toyama, 3190 Gofuku, Toyma-shi, Toyama, 930-8555, Japan
| | - Reiko Genmei
- Frontier Research Core for Life Sciences, University of Toyama, 3190 Gofuku, Toyma-shi, Toyama, 930-8555, Japan
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21
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Li X, Thompson D, Kumar B, DeMartino GN. Molecular and cellular roles of PI31 (PSMF1) protein in regulation of proteasome function. J Biol Chem 2014; 289:17392-405. [PMID: 24770418 DOI: 10.1074/jbc.m114.561183] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We investigated molecular features and cellular roles of PI31 (PSMF1) on regulation of proteasome function. PI31 has a C-terminal HbYX (where Hb is a hydrophobic amino acid, Y is tyrosine, and X is any amino acid) motif characteristic of several proteasome activators. Peptides corresponding to the PI31 C terminus also bind to and activate the 20 S proteasome in an HbYX-dependent manner, but intact PI31protein inhibits in vitro 20 S activity. Binding to and inhibition of the proteasome by PI31 are conferred by the HbYX-containing proline-rich C-terminal domain but do not require HbYX residues. Thus, multiple regions of PI31 bind independently to the proteasome and collectively determine effects on activity. PI31 blocks the ATP-dependent in vitro assembly of 26 S proteasome from 20 S proteasome and PA700 subcomplexes but has no effect on in vitro activity of the intact 26 S proteasome. To determine the physiologic significance of these in vitro effects, we assessed multiple aspects of cellular proteasome content and function after altering PI31 levels. We detected no change in overall cellular proteasome content or function when PI31 levels were either increased by moderate ectopic overexpression or decreased by RNA interference (RNAi). We also failed to identify a role of PI31 ADP-ribosylation as a mechanism for regulation of overall 26 S proteasome content and function, as recently proposed. Thus, despite its in vitro effects on various proteasome activities and its structural relationship to established proteasome regulators, cellular roles and mechanisms of PI31 in regulation of proteasome function remain unclear and require future definition.
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Affiliation(s)
- Xiaohua Li
- From the Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390
| | - David Thompson
- From the Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390
| | - Brajesh Kumar
- From the Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390
| | - George N DeMartino
- From the Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390
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22
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Abstract
The ubiquitin proteasome system (UPS) is the main ATP-dependent protein degradation pathway in the cytosol and nucleus of eukaryotic cells. At its centre is the 26S proteasome, which degrades regulatory proteins and misfolded or damaged proteins. In a major breakthrough, several groups have determined high-resolution structures of the entire 26S proteasome particle in different nucleotide conditions and with and without substrate using cryo-electron microscopy combined with other techniques. These structures provide some surprising insights into the functional mechanism of the proteasome and will give invaluable guidance for genetic and biochemical studies of this key regulatory system.
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23
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Deep classification of a large cryo-EM dataset defines the conformational landscape of the 26S proteasome. Proc Natl Acad Sci U S A 2014; 111:5544-9. [PMID: 24706844 DOI: 10.1073/pnas.1403409111] [Citation(s) in RCA: 151] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
The 26S proteasome is a 2.5 MDa molecular machine that executes the degradation of substrates of the ubiquitin-proteasome pathway. The molecular architecture of the 26S proteasome was recently established by cryo-EM approaches. For a detailed understanding of the sequence of events from the initial binding of polyubiquitylated substrates to the translocation into the proteolytic core complex, it is necessary to move beyond static structures and characterize the conformational landscape of the 26S proteasome. To this end we have subjected a large cryo-EM dataset acquired in the presence of ATP and ATP-γS to a deep classification procedure, which deconvolutes coexisting conformational states. Highly variable regions, such as the density assigned to the largest subunit, Rpn1, are now well resolved and rendered interpretable. Our analysis reveals the existence of three major conformations: in addition to the previously described ATP-hydrolyzing (ATPh) and ATP-γS conformations, an intermediate state has been found. Its AAA-ATPase module adopts essentially the same topology that is observed in the ATPh conformation, whereas the lid is more similar to the ATP-γS bound state. Based on the conformational ensemble of the 26S proteasome in solution, we propose a mechanistic model for substrate recognition, commitment, deubiquitylation, and translocation into the core particle.
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24
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Reconstitution of the 26S proteasome reveals functional asymmetries in its AAA+ unfoldase. Nat Struct Mol Biol 2013; 20:1164-72. [PMID: 24013205 PMCID: PMC3869383 DOI: 10.1038/nsmb.2659] [Citation(s) in RCA: 111] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2013] [Accepted: 07/26/2013] [Indexed: 12/25/2022]
Abstract
The 26S proteasome is the major eukaryotic ATP-dependent protease, yet the detailed mechanisms used by the proteasomal heterohexameric AAA+ unfoldase to drive substrate degradation remain poorly understood. To perform systematic mutational analyses of individual ATPase subunits, we heterologously expressed the unfoldase subcomplex from Saccharomyces cerevisiae in Escherichia coli and reconstituted the proteasome in vitro. Our studies demonstrate that the six ATPases have distinct roles in degradation, corresponding to their positions in the spiral staircases adopted by the AAA+ domains in the absence or presence of substrate. ATP hydrolysis in subunits at the top of the staircases is critical for substrate engagement and translocation. Whereas the unfoldase relies on this vertical asymmetry for substrate processing, interaction with the peptidase exhibits three-fold symmetry with contributions from alternate subunits. These diverse functional asymmetries highlight how the 26S proteasome deviates from simpler, homomeric AAA+ proteases.
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25
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De La Mota-Peynado A, Lee SYC, Pierce BM, Wani P, Singh CR, Roelofs J. The proteasome-associated protein Ecm29 inhibits proteasomal ATPase activity and in vivo protein degradation by the proteasome. J Biol Chem 2013; 288:29467-81. [PMID: 23995839 DOI: 10.1074/jbc.m113.491662] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Several proteasome-associated proteins regulate degradation by the 26 S proteasome using the ubiquitin chains that mark most substrates for degradation. The proteasome-associated protein Ecm29, however, has no ubiquitin-binding or modifying activity, and its direct effect on substrate degradation is unclear. Here, we show that Ecm29 acts as a proteasome inhibitor. Besides inhibiting the proteolytic cleavage of peptide substrates in vitro, it inhibits the degradation of ubiquitin-dependent and -independent substrates in vivo. Binding of Ecm29 to the proteasome induces a closed conformation of the substrate entry channel of the core particle. Furthermore, Ecm29 inhibits proteasomal ATPase activity, suggesting that the mechanism of inhibition and gate regulation by Ecm29 is through regulation of the proteasomal ATPases. Consistent with this, we identified through chemical cross-linking that Ecm29 binds to, or in close proximity to, the proteasomal ATPase subunit Rpt5. Additionally, we show that Ecm29 preferentially associates with both mutant and nucleotide depleted proteasomes. We propose that the inhibitory ability of Ecm29 is important for its function as a proteasome quality control factor by ensuring that aberrant proteasomes recognized by Ecm29 are inactive.
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26
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Peth A, Nathan JA, Goldberg AL. The ATP costs and time required to degrade ubiquitinated proteins by the 26 S proteasome. J Biol Chem 2013; 288:29215-22. [PMID: 23965995 DOI: 10.1074/jbc.m113.482570] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The degradation of ubiquitinated proteins by 26 S proteasomes requires ATP hydrolysis. To investigate if the six proteasomal ATPases function independently or in a cyclic manner, as proposed recently, we used yeast mutants that prevent ATP binding to Rpt3, Rpt5, or Rpt6. Although proteasomes contain six ATPase subunits, each of these single mutations caused a 66% reduction in basal ATP hydrolysis, and each blocked completely the 2-3-fold stimulation of ATPase activity induced by ubiquitinated substrates. Therefore, the ATPase subunits must function in a ordered manner, in which each is required for the stimulation of ATPase activity by substrates. Although ATP is essential for multiple steps in proteasome function, when the rate of ATP hydrolysis was reduced incrementally, the degradation of Ub5-DHFR (where Ub is ubiquitin and DHFR is dihydrofolate reductase) decreased exactly in parallel. This direct proportionality implies that a specific number of ATPs is consumed in degrading a ubiquitinated protein. When the ubiquitinated DHFR was more tightly folded (upon addition of the ligand folate), the rate of ATP hydrolysis was unchanged, but the time to degrade a Ub5-DHFR molecule (∼13 s) and the energy expenditure (50-80 ATPs/Ub5-DHFR) both increased by 2-fold. With a mutation in the ATPase C terminus that reduced gate opening into the 20 S proteasome, the energy costs and time required for conjugate degradation also increased. Thus, different ubiquitin conjugates activate similarly the ATPase subunit cycle that drives proteolysis, but polypeptide structure determines the time required for degradation and thus the energy cost.
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Affiliation(s)
- Andreas Peth
- From the Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115 and
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27
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Lei D, Li F, Su H, Liu J, Wei N, Wang X. Hepatic deficiency of COP9 signalosome subunit 8 induces ubiquitin-proteasome system impairment and Bim-mediated apoptosis in murine livers. PLoS One 2013; 8:e67793. [PMID: 23840878 PMCID: PMC3698095 DOI: 10.1371/journal.pone.0067793] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2013] [Accepted: 05/27/2013] [Indexed: 11/19/2022] Open
Abstract
The COP9 signalosome (CSN), an evolutionally highly conserved protein complex composed of 8 unique subunits (CSN1 through CSN8) in higher eukaryotes, is purported to modulate protein degradation mediated by the ubiquitin-proteasome system (UPS) but this has not been demonstrated in a critical mitotic parenchymal organ of vertebrates. Hepatocyte-specific knockout of the Cops8 gene (HS-Csn8KO) was shown to cause massive hepatocyte apoptosis and liver malfunction but the underlying mechanism remains unclear. Here, we report that Csn8/CSN exerts profound impacts on hepatic UPS function and is critical to the stability of the pro-apoptotic protein Bim. Significant decreases in CIS (cytokine-inducible Src homology 2 domain-containing protein), a Bim receptor of a cullin2-based ubiquitin ligase, were found to co-exist with a marked increase of Bim proteins. Csn8 deficiency also significantly decreased 19S proteasome subunit Rpt5 and markedly increased high molecular weight neddylated and ubiquitinated proteins. The use of a surrogate UPS substrate further reveals severe impairment of UPS-mediated proteolysis in HS-Csn8KO livers. Inclusion body-like materials were accumulated in Csn8 deficient hepatocytes. In addition to Bim, massive hepatocyte apoptosis in HS-Csn8KO livers is also associated with elevated expression of other members of the Bcl2 family, including pro-apoptotic Bax as well as anti-apoptotic Bcl2 and Bcl-XL. Increased interaction between Bcl2 and Bim, but not between Bcl2 and Bax, was detected. Hence, it is concluded that hepatic CSN8 deficiency impairs the UPS in the liver and the resultant Bim upregulation likely plays an important role in triggering hepatocyte apoptosis via sequestering Bcl2 away from Bax.
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Affiliation(s)
- Daoxiong Lei
- Division of Basic Biomedical Sciences, The University of South Dakota Sanford School of Medicine, Vermillion, South Dakota, United States of America
- Department of Hepatobiliary Surgery, Tianjin 4th Central Hospital and The 4th Central Clinical College of Tianjin Medical University, Tianjin, China
| | - Faqian Li
- Department of Pathology and Laboratory Medicine, University of Rochester Medical Center, Rochester, New York, United States of America
| | - Huabo Su
- Division of Basic Biomedical Sciences, The University of South Dakota Sanford School of Medicine, Vermillion, South Dakota, United States of America
- Vascular Biology Center and Department of Pharmacology and Toxicology, Medical College of Georgia, Georgia Regents University, Augusta, Georgia, United States of America
| | - Jinbao Liu
- Division of Basic Biomedical Sciences, The University of South Dakota Sanford School of Medicine, Vermillion, South Dakota, United States of America
- Department of Pathophysiology, Guangzhou Medical College, Guangzhou, Guangdong, China
| | - Ning Wei
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut, United States of America
| | - Xuejun Wang
- Division of Basic Biomedical Sciences, The University of South Dakota Sanford School of Medicine, Vermillion, South Dakota, United States of America
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28
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Conformational switching of the 26S proteasome enables substrate degradation. Nat Struct Mol Biol 2013; 20:781-8. [PMID: 23770819 PMCID: PMC3712289 DOI: 10.1038/nsmb.2616] [Citation(s) in RCA: 195] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2013] [Accepted: 05/14/2013] [Indexed: 02/07/2023]
Abstract
The 26S proteasome is the major eukaryotic ATP-dependent protease, responsible for regulating the proteome through degradation of ubiquitin-tagged substrates. Its regulatory particle, containing the heterohexameric AAA+ ATPase motor and the essential deubiquitinase Rpn11, recognizes substrates, removes their ubiquitin chains, and translocates them into the associated peptidase after unfolding, but detailed mechanisms remain unknown. Here we present the first structure of the 26S proteasome from S. cerevisiae during substrate degradation, showing that the regulatory particle switches from a pre-engaged to a translocation-competent conformation. This conformation is characterized by a rearranged ATPase ring with uniform subunit interfaces, a widened central channel coaxially aligned with the peptidase, and a spiral orientation of pore loops that suggests a rapid progression of ATP-hydrolysis events around the ring. Importantly, Rpn11 moves from an occluded position to directly above the central pore, facilitating substrate deubiquitination concomitant with translocation.
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29
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Śledź P, Unverdorben P, Beck F, Pfeifer G, Schweitzer A, Förster F, Baumeister W. Structure of the 26S proteasome with ATP-γS bound provides insights into the mechanism of nucleotide-dependent substrate translocation. Proc Natl Acad Sci U S A 2013; 110:7264-9. [PMID: 23589842 PMCID: PMC3645540 DOI: 10.1073/pnas.1305782110] [Citation(s) in RCA: 128] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The 26S proteasome is a 2.5-MDa, ATP-dependent multisubunit proteolytic complex that processively destroys proteins carrying a degradation signal. The proteasomal ATPase heterohexamer is a key module of the 19S regulatory particle; it unfolds substrates and translocates them into the 20S core particle where degradation takes place. We used cryoelectron microscopy single-particle analysis to obtain insights into the structural changes of 26S proteasome upon the binding and hydrolysis of ATP. The ATPase ring adopts at least two distinct helical staircase conformations dependent on the nucleotide state. The transition from the conformation observed in the presence of ATP to the predominant conformation in the presence of ATP-γS induces a sliding motion of the ATPase ring over the 20S core particle ring leading to an alignment of the translocation channels of the ATPase and the core particle gate, a conformational state likely to facilitate substrate translocation. Two types of intersubunit modules formed by the large ATPase domain of one ATPase subunit and the small ATPase domain of its neighbor exist. They resemble the contacts observed in the crystal structures of ClpX and proteasome-activating nucleotidase, respectively. The ClpX-like contacts are positioned consecutively and give rise to helical shape in the hexamer, whereas the proteasome-activating nucleotidase-like contact is required to close the ring. Conformational switching between these forms allows adopting different helical conformations in different nucleotide states. We postulate that ATP hydrolysis by the regulatory particle ATPase (Rpt) 5 subunit initiates a cascade of conformational changes, leading to pulling of the substrate, which is primarily executed by Rpt1, Rpt2, and Rpt6.
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Affiliation(s)
- Paweł Śledź
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Pia Unverdorben
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Florian Beck
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Günter Pfeifer
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Andreas Schweitzer
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Friedrich Förster
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Wolfgang Baumeister
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
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