1
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Yang M, Chen S, Lim SL, Yang L, Zhong JY, Chan KC, Zhao Z, Wong KB, Wang J, Lim BL. A converged ubiquitin-proteasome pathway for the degradation of TOC and TOM tail-anchored receptors. JOURNAL OF INTEGRATIVE PLANT BIOLOGY 2024; 66:1007-1023. [PMID: 38501483 DOI: 10.1111/jipb.13645] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Accepted: 02/27/2024] [Indexed: 03/20/2024]
Abstract
In plants, thousands of nucleus-encoded proteins translated in the cytosol are sorted to chloroplasts and mitochondria by binding to specific receptors of the TOC (translocon on the outer chloroplast membrane) and the TOM (translocon on the outer mitochondrial membrane) complexes for import into those organelles. The degradation pathways for these receptors are unclear. Here, we discovered a converged ubiquitin-proteasome pathway for the degradation of Arabidopsis thaliana TOC and TOM tail-anchored receptors. The receptors are ubiquitinated by E3 ligase(s) and pulled from the outer membranes by the AAA+ adenosine triphosphatase CDC48, after which a previously uncharacterized cytosolic protein, transmembrane domain (TMD)-binding protein for tail-anchored outer membrane proteins (TTOP), binds to the exposed TMDs at the C termini of the receptors and CDC48, and delivers these complexes to the 26S proteasome.
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Affiliation(s)
- Meijing Yang
- School of Biological Sciences, University of Hong Kong, Pokfulam, 999077, Hong Kong, China
- Department of Biology, Southern University of Science and Technology, Shenzhen, 518055, China
| | - Shuai Chen
- School of Biomedical Engineering, Shenzhen University, Shenzhen, 518060, China
- School of Life Sciences, The Chinese University of Hong Kong, Shatin, 999077, Hong Kong, China
| | - Shey-Li Lim
- School of Biological Sciences, University of Hong Kong, Pokfulam, 999077, Hong Kong, China
| | - Lang Yang
- School of Biological Sciences, University of Hong Kong, Pokfulam, 999077, Hong Kong, China
- Department of Biology, Southern University of Science and Technology, Shenzhen, 518055, China
| | - Jia Yi Zhong
- School of Biological Sciences, University of Hong Kong, Pokfulam, 999077, Hong Kong, China
| | - Koon Chuen Chan
- School of Biological Sciences, University of Hong Kong, Pokfulam, 999077, Hong Kong, China
| | - Zhizhu Zhao
- School of Biological Sciences, University of Hong Kong, Pokfulam, 999077, Hong Kong, China
| | - Kam-Bo Wong
- School of Life Sciences, The Chinese University of Hong Kong, Shatin, 999077, Hong Kong, China
- State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Shatin, 999077, Hong Kong, China
| | - Junqi Wang
- Department of Biology, Southern University of Science and Technology, Shenzhen, 518055, China
| | - Boon Leong Lim
- School of Biological Sciences, University of Hong Kong, Pokfulam, 999077, Hong Kong, China
- State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Shatin, 999077, Hong Kong, China
- HKU Shenzhen Institute of Research and Innovation, Shenzhen, 518052, China
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2
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Marathe S, Grotewold E, Otegui MS. Should I stay or should I go? Trafficking of plant extra-nuclear transcription factors. THE PLANT CELL 2024; 36:1524-1539. [PMID: 38163635 PMCID: PMC11062434 DOI: 10.1093/plcell/koad277] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2023] [Accepted: 09/21/2023] [Indexed: 01/03/2024]
Abstract
At the heart of all biological processes lies the control of nuclear gene expression, which is primarily achieved through the action of transcription factors (TFs) that generally contain a nuclear localization signal (NLS) to facilitate their transport into the nucleus. However, some TFs reside in the cytoplasm in a transcriptionally inactive state and only enter the nucleus in response to specific signals, which in plants include biotic or abiotic stresses. These extra-nuclear TFs can be found in the cytosol or associated with various membrane systems, including the endoplasmic reticulum and plasma membrane. They may be integral proteins with transmembrane domains or associate peripherally with the lipid bilayer via acylation or membrane-binding domains. Although over 30 plant TFs, most of them involved in stress responses, have been experimentally shown to reside outside the nucleus, computational predictions suggest that this number is much larger. Understanding how extra-nuclear TFs are trafficked into the nucleus is essential for reconstructing transcriptional regulatory networks that govern major cellular pathways in response to biotic and abiotic signals. Here, we provide a perspective on what is known on plant extranuclear-nuclear TF retention, nuclear trafficking, and the post-translational modifications that ultimately enable them to regulate gene expression upon entering the nucleus.
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Affiliation(s)
- Sarika Marathe
- Department of Botany, University of Wisconsin-Madison, Madison, WI 53706, USA
- Center for Quantitative Cell Imaging, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Erich Grotewold
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824-6473, USA
| | - Marisa S Otegui
- Department of Botany, University of Wisconsin-Madison, Madison, WI 53706, USA
- Center for Quantitative Cell Imaging, University of Wisconsin-Madison, Madison, WI 53706, USA
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3
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Oh J, Kim DK, Ahn SH, Kim HM, Cho H. A dual role of the conserved PEX19 helix in safeguarding peroxisomal membrane proteins. iScience 2024; 27:109537. [PMID: 38585659 PMCID: PMC10995880 DOI: 10.1016/j.isci.2024.109537] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2023] [Revised: 02/13/2024] [Accepted: 03/18/2024] [Indexed: 04/09/2024] Open
Abstract
Accurate localization of membrane proteins is essential for proper cellular functioning and the integrity of cellular membranes. Post-translational targeting of peroxisomal membrane proteins (PMPs) is mediated by the cytosolic chaperone PEX19 and its membrane receptor PEX3. However, the molecular mechanisms underlying PMP targeting are poorly understood. Here, using biochemical and mass spectrometry analysis, we find that a conserved PEX19 helix, αd, is critical to prevent improper exposure of the PEX26 transmembrane domain (TMD) to cytosolic chaperones. Furthermore, the αd helix of PEX19 interacts with the cytosolic domain of the PEX3 receptor, thereby triggering PEX26 release at the correct destination membrane. The peroxisome-deficient PEX3-G138E mutant completely abolishes this secondary interaction, leading to lack of PEX3-induced PEX26 release from PEX19. These findings elucidate a dual molecular mechanism that is essential to membrane protein protection and destination-specific release by a molecular chaperone.
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Affiliation(s)
- Jeonghyun Oh
- Center for Biomolecular and Cellular Structure, Institute for Basic Science (IBS), Daejeon 34126, Republic of Korea
| | - Do Kyung Kim
- Center for Biomolecular and Cellular Structure, Institute for Basic Science (IBS), Daejeon 34126, Republic of Korea
| | - Seung Hae Ahn
- Center for Biomolecular and Cellular Structure, Institute for Basic Science (IBS), Daejeon 34126, Republic of Korea
| | - Ho Min Kim
- Center for Biomolecular and Cellular Structure, Institute for Basic Science (IBS), Daejeon 34126, Republic of Korea
- Graduate School of Medical Science & Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
| | - Hyunju Cho
- Center for Biomolecular and Cellular Structure, Institute for Basic Science (IBS), Daejeon 34126, Republic of Korea
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4
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Zhu Q, Zhu X, Zhang L. ER membrane complex (EMC): Structure, functions, and roles in diseases. FASEB J 2024; 38:e23539. [PMID: 38498340 DOI: 10.1096/fj.202302266r] [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: 11/02/2023] [Revised: 01/22/2024] [Accepted: 02/21/2024] [Indexed: 03/20/2024]
Abstract
The endoplasmic reticulum (ER) is the largest membrane system in eukaryotic cells and is the primary site for the biosynthesis of lipids and carbohydrates, as well as for the folding, assembly, modification, and transport of secreted and integrated membrane proteins. The ER membrane complex (EMC) on the ER membrane is an ER multiprotein complex that affects the quality control of membrane proteins, which is abundant and widely preserved. Its disruption has been found to affect a wide range of processes, including protein and lipid synthesis, organelle communication, endoplasmic reticulum stress, and viral maturation, and may lead to neurodevelopmental disorders and cancer. Therefore, EMC has attracted the attention of many scholars and become a hot field. In this paper, we summarized the main contributions of the research of EMC in the past nearly 15 years, and reviewed the structure and function of EMC as well as its related diseases. We hope this review will promote further progress of research on EMC.
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Affiliation(s)
- Qi Zhu
- The Sichuan Provincial Key Laboratory for Human Disease Gene Study and Department of Laboratory Medicine, Center for Medical Genetics, Sichuan Provincial People's Hospital, School of Medicine, University of Electronic Science and Technology of China, Chengdu, Sichuan, China
| | - Xianjun Zhu
- The Sichuan Provincial Key Laboratory for Human Disease Gene Study and Department of Laboratory Medicine, Center for Medical Genetics, Sichuan Provincial People's Hospital, School of Medicine, University of Electronic Science and Technology of China, Chengdu, Sichuan, China
| | - Lin Zhang
- The Sichuan Provincial Key Laboratory for Human Disease Gene Study and Department of Laboratory Medicine, Center for Medical Genetics, Sichuan Provincial People's Hospital, School of Medicine, University of Electronic Science and Technology of China, Chengdu, Sichuan, China
- Qinghai Provincial Key Laboratory of Tibetan Medicine Research, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, Qinghai, China
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5
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Sun S, Zhao G, Jia M, Jiang Q, Li S, Wang H, Li W, Wang Y, Bian X, Zhao YG, Huang X, Yang G, Cai H, Pastor-Pareja JC, Ge L, Zhang C, Hu J. Stay in touch with the endoplasmic reticulum. SCIENCE CHINA. LIFE SCIENCES 2024; 67:230-257. [PMID: 38212460 DOI: 10.1007/s11427-023-2443-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2023] [Accepted: 08/28/2023] [Indexed: 01/13/2024]
Abstract
The endoplasmic reticulum (ER), which is composed of a continuous network of tubules and sheets, forms the most widely distributed membrane system in eukaryotic cells. As a result, it engages a variety of organelles by establishing membrane contact sites (MCSs). These contacts regulate organelle positioning and remodeling, including fusion and fission, facilitate precise lipid exchange, and couple vital signaling events. Here, we systematically review recent advances and converging themes on ER-involved organellar contact. The molecular basis, cellular influence, and potential physiological functions for ER/nuclear envelope contacts with mitochondria, Golgi, endosomes, lysosomes, lipid droplets, autophagosomes, and plasma membrane are summarized.
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Affiliation(s)
- Sha Sun
- National Laboratory of Biomacromolecules, Institute of Biophysics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100101, China
| | - Gan Zhao
- The Ministry of Education Key Laboratory of Cell Proliferation and Differentiation, College of Life Sciences, Peking University, Beijing, 100871, China
| | - Mingkang Jia
- The Ministry of Education Key Laboratory of Cell Proliferation and Differentiation, College of Life Sciences, Peking University, Beijing, 100871, China
| | - Qing Jiang
- The Ministry of Education Key Laboratory of Cell Proliferation and Differentiation, College of Life Sciences, Peking University, Beijing, 100871, China
| | - Shulin Li
- State Key Laboratory of Membrane Biology, Tsinghua-Peking Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Haibin Wang
- National Laboratory of Biomacromolecules, Institute of Biophysics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100101, China
| | - Wenjing Li
- Laboratory of Computational Biology & Machine Intelligence, School of Artificial Intelligence, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Yunyun Wang
- State Key Laboratory of Medicinal Chemical Biology, College of Life Sciences, Nankai University, Tianjin, 300071, China
| | - Xin Bian
- State Key Laboratory of Medicinal Chemical Biology, College of Life Sciences, Nankai University, Tianjin, 300071, China.
| | - Yan G Zhao
- Brain Research Center, Department of Biology, School of Life Sciences, Southern University of Science and Technology, Shenzhen, 518055, China.
| | - Xun Huang
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Innovation Academy for Seed Design, Chinese Academy of Sciences, Beijing, 100101, China.
| | - Ge Yang
- Laboratory of Computational Biology & Machine Intelligence, School of Artificial Intelligence, University of Chinese Academy of Sciences, Beijing, 100049, China.
| | - Huaqing Cai
- National Laboratory of Biomacromolecules, Institute of Biophysics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100101, China.
| | - Jose C Pastor-Pareja
- State Key Laboratory of Membrane Biology, Tsinghua-Peking Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing, 100084, China.
- Institute of Neurosciences, Consejo Superior de Investigaciones Cientfflcas-Universidad Miguel Hernandez, San Juan de Alicante, 03550, Spain.
| | - Liang Ge
- State Key Laboratory of Membrane Biology, Tsinghua-Peking Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing, 100084, China.
| | - Chuanmao Zhang
- The Ministry of Education Key Laboratory of Cell Proliferation and Differentiation, College of Life Sciences, Peking University, Beijing, 100871, China.
| | - Junjie Hu
- National Laboratory of Biomacromolecules, Institute of Biophysics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100101, China.
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6
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Cho H, Liu Y, Chung S, Chandrasekar S, Weiss S, Shan SO. Dynamic stability of Sgt2 enables selective and privileged client handover in a chaperone triad. Nat Commun 2024; 15:134. [PMID: 38167697 PMCID: PMC10761869 DOI: 10.1038/s41467-023-44260-5] [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: 03/24/2023] [Accepted: 12/06/2023] [Indexed: 01/05/2024] Open
Abstract
Membrane protein biogenesis poses acute challenges to protein homeostasis, and how they are selectively escorted to the target membrane is not well understood. Here we address this question in the guided-entry-of-tail-anchored protein (GET) pathway, in which tail-anchored membrane proteins (TAs) are relayed through an Hsp70-Sgt2-Get3 chaperone triad for targeting to the endoplasmic reticulum. We show that the Hsp70 ATPase cycle and TA substrate drive dimeric Sgt2 from a wide-open conformation to a closed state, in which TAs are protected by both substrate binding domains of Sgt2. Get3 is privileged to receive TA from closed Sgt2, whereas off-pathway chaperones remove TAs from open Sgt2. Sgt2 closing is less favorable with suboptimal GET substrates, which are rejected during or after the Hsp70-to-Sgt2 handover. Our results demonstrate how fine-tuned conformational dynamics in Sgt2 enable hydrophobic TAs to be effectively funneled onto their dedicated targeting factor while also providing a mechanism for substrate selection.
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Affiliation(s)
- Hyunju Cho
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
- Center for Biomolecular and Cellular Structure, Institute for Basic Science, Daejeon, 34126, Republic of Korea
| | - Yumeng Liu
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
- Biochemistry and Molecular Biotechnology Department, University of Massachusetts Chan Medical School, Worcester, MA, 01655, USA
| | - SangYoon Chung
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, CA, 90095, USA
| | - Sowmya Chandrasekar
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Shimon Weiss
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, CA, 90095, USA
- Department of Physics, Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan, 52900, Israel
| | - Shu-Ou Shan
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, 91125, USA.
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7
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Shimamoto K, Fujikawa K, Osawa T, Mori S, Nomura K, Nishiyama KI. Key contributions of a glycolipid to membrane protein integration. PROCEEDINGS OF THE JAPAN ACADEMY. SERIES B, PHYSICAL AND BIOLOGICAL SCIENCES 2024; 100:387-413. [PMID: 39085064 DOI: 10.2183/pjab.100.026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/02/2024]
Abstract
Regulation of membrane protein integration involves molecular devices such as Sec-translocons or the insertase YidC. We have identified an integration-promoting factor in the inner membrane of Escherichia coli called membrane protein integrase (MPIase). Structural analysis revealed that, despite its enzyme-like name, MPIase is a glycolipid with a long glycan comprising N-acetyl amino sugars, a pyrophosphate linker, and a diacylglycerol (DAG) anchor. Additionally, we found that DAG, a minor membrane component, blocks spontaneous integration. In this review, we demonstrate how they contribute to Sec-independent membrane protein integration in bacteria using a comprehensive approach including synthetic chemistry and biophysical analyses. DAG blocks unfavorable spontaneous integrations by suppressing mobility in the membrane core, whereas MPIase compensates for this. Moreover, MPIase plays critical roles in capturing a substrate protein to prevent its aggregation, attracting it to the membrane surface, facilitating its insertion into the membrane, and delivering it to other factors. The combination of DAG and MPIase efficiently regulates the integration of membrane proteins.
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Affiliation(s)
- Keiko Shimamoto
- Bioorganic Research Institute, Suntory Foundation for Life Sciences, Seika-cho, Soraku-gun, Kyoto, Japan
- Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan
| | - Kohki Fujikawa
- Bioorganic Research Institute, Suntory Foundation for Life Sciences, Seika-cho, Soraku-gun, Kyoto, Japan
| | - Tsukiho Osawa
- Bioorganic Research Institute, Suntory Foundation for Life Sciences, Seika-cho, Soraku-gun, Kyoto, Japan
| | - Shoko Mori
- Bioorganic Research Institute, Suntory Foundation for Life Sciences, Seika-cho, Soraku-gun, Kyoto, Japan
| | - Kaoru Nomura
- Bioorganic Research Institute, Suntory Foundation for Life Sciences, Seika-cho, Soraku-gun, Kyoto, Japan
| | - Ken-Ichi Nishiyama
- Department of Biological Chemistry and Food Sciences, Faculty of Agriculture, Iwate University, Morioka, Iwate, Japan
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8
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Stewart H, Lu Y, O’Keefe S, Valpadashi A, Cruz-Zaragoza LD, Michel HA, Nguyen SK, Carnell GW, Lukhovitskaya N, Milligan R, Adewusi Y, Jungreis I, Lulla V, Matthews DA, High S, Rehling P, Emmott E, Heeney JL, Davidson AD, Edgar JR, Smith GL, Firth AE. The SARS-CoV-2 protein ORF3c is a mitochondrial modulator of innate immunity. iScience 2023; 26:108080. [PMID: 37860693 PMCID: PMC10583119 DOI: 10.1016/j.isci.2023.108080] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2022] [Revised: 08/06/2023] [Accepted: 09/25/2023] [Indexed: 10/21/2023] Open
Abstract
The SARS-CoV-2 genome encodes a multitude of accessory proteins. Using comparative genomic approaches, an additional accessory protein, ORF3c, has been predicted to be encoded within the ORF3a sgmRNA. Expression of ORF3c during infection has been confirmed independently by ribosome profiling. Despite ORF3c also being present in the 2002-2003 SARS-CoV, its function has remained unexplored. Here we show that ORF3c localizes to mitochondria, where it inhibits innate immunity by restricting IFN-β production, but not NF-κB activation or JAK-STAT signaling downstream of type I IFN stimulation. We find that ORF3c is inhibitory after stimulation with cytoplasmic RNA helicases RIG-I or MDA5 or adaptor protein MAVS, but not after TRIF, TBK1 or phospho-IRF3 stimulation. ORF3c co-immunoprecipitates with the antiviral proteins MAVS and PGAM5 and induces MAVS cleavage by caspase-3. Together, these data provide insight into an uncharacterized mechanism of innate immune evasion by this important human pathogen.
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Affiliation(s)
- Hazel Stewart
- Department of Pathology, University of Cambridge, Cambridge, UK
| | - Yongxu Lu
- Department of Pathology, University of Cambridge, Cambridge, UK
| | - Sarah O’Keefe
- Faculty of Biology, Medicine and Health, School of Biological Sciences, University of Manchester, Manchester, UK
| | - Anusha Valpadashi
- Department of Cellular Biochemistry, University Medical Center Göttingen, Göttingen, Germany
| | | | | | | | - George W. Carnell
- Department of Veterinary Medicine, University of Cambridge, Cambridge, UK
| | | | - Rachel Milligan
- School of Cellular and Molecular Medicine, Faculty of Life Sciences, University of Bristol, Bristol, UK
| | - Yasmin Adewusi
- Department of Pathology, University of Cambridge, Cambridge, UK
| | - Irwin Jungreis
- Broad Institute of MIT and Harvard, Cambridge, MA, USA
- MIT Computer Science and Artificial Intelligence Laboratory, Cambridge, MA, USA
| | - Valeria Lulla
- Department of Pathology, University of Cambridge, Cambridge, UK
| | - David A. Matthews
- School of Cellular and Molecular Medicine, Faculty of Life Sciences, University of Bristol, Bristol, UK
| | - Stephen High
- Faculty of Biology, Medicine and Health, School of Biological Sciences, University of Manchester, Manchester, UK
| | - Peter Rehling
- Department of Cellular Biochemistry, University Medical Center Göttingen, Göttingen, Germany
| | - Edward Emmott
- Centre for Proteome Research, Department of Biochemistry & Systems Biology, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, UK
| | - Jonathan L. Heeney
- Department of Veterinary Medicine, University of Cambridge, Cambridge, UK
| | - Andrew D. Davidson
- School of Cellular and Molecular Medicine, Faculty of Life Sciences, University of Bristol, Bristol, UK
| | - James R. Edgar
- Department of Pathology, University of Cambridge, Cambridge, UK
| | | | - Andrew E. Firth
- Department of Pathology, University of Cambridge, Cambridge, UK
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9
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Pleiner T, Hazu M, Pinton Tomaleri G, Nguyen VN, Januszyk K, Voorhees RM. A selectivity filter in the ER membrane protein complex limits protein misinsertion at the ER. J Cell Biol 2023; 222:e202212007. [PMID: 37199759 PMCID: PMC10200711 DOI: 10.1083/jcb.202212007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2022] [Revised: 03/31/2023] [Accepted: 04/20/2023] [Indexed: 05/19/2023] Open
Abstract
Tail-anchored (TA) proteins play essential roles in mammalian cells, and their accurate localization is critical for proteostasis. Biophysical similarities lead to mistargeting of mitochondrial TA proteins to the ER, where they are delivered to the insertase, the ER membrane protein complex (EMC). Leveraging an improved structural model of the human EMC, we used mutagenesis and site-specific crosslinking to map the path of a TA protein from its cytosolic capture by methionine-rich loops to its membrane insertion through a hydrophilic vestibule. Positively charged residues at the entrance to the vestibule function as a selectivity filter that uses charge-repulsion to reject mitochondrial TA proteins. Similarly, this selectivity filter retains the positively charged soluble domains of multipass substrates in the cytosol, thereby ensuring they adopt the correct topology and enforcing the "positive-inside" rule. Substrate discrimination by the EMC provides a biochemical explanation for one role of charge in TA protein sorting and protects compartment integrity by limiting protein misinsertion.
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Affiliation(s)
- Tino Pleiner
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Masami Hazu
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Giovani Pinton Tomaleri
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Vy N. Nguyen
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Kurt Januszyk
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Rebecca M. Voorhees
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
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10
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Rapaport D, Herrmann JM. Chasing the right tail: How the ER membrane complex recognizes its substrates. J Cell Biol 2023; 222:e202306035. [PMID: 37436711 PMCID: PMC10337602 DOI: 10.1083/jcb.202306035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/13/2023] Open
Abstract
Tail-anchored proteins are tethered to membranes of the ER, mitochondria, and peroxisomes. In this issue, Pleiner and colleagues (2023. J. Cell Biol.https://doi.org/10.1083/jcb.202212007) show that the ER membrane complex (EMC) uses an inbuilt charge-dependent selectivity filter to specifically insert ER tail-anchored proteins according to their topology signals and to prevent the misincorporation of mitochondrial proteins.
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Affiliation(s)
- Doron Rapaport
- Interfaculty Institute of Biochemistry, University of Tübingen, Tübingen, Germany
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11
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Tipper DJ, Harley CA. Spf1 and Ste24: quality controllers of transmembrane protein topology in the eukaryotic cell. Front Cell Dev Biol 2023; 11:1220441. [PMID: 37635876 PMCID: PMC10456885 DOI: 10.3389/fcell.2023.1220441] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Accepted: 07/14/2023] [Indexed: 08/29/2023] Open
Abstract
DNA replication, transcription, and translation in eukaryotic cells occur with decreasing but still high fidelity. In contrast, for the estimated 33% of the human proteome that is inserted as transmembrane (TM) proteins, insertion with a non-functional inverted topology is frequent. Correct topology is essential for function and trafficking to appropriate cellular compartments and is controlled principally by responses to charged residues within 15 residues of the inserted TM domain (TMD); the flank with the higher positive charge remains in the cytosol (inside), following the positive inside rule (PIR). Yeast (Saccharomyces cerevisiae) mutants that increase insertion contrary to the PIR were selected. Mutants with strong phenotypes were found only in SPF1 and STE24 (human cell orthologs are ATP13A1 and ZMPSte24) with, at the time, no known relevant functions. Spf1/Atp13A1 is now known to dislocate to the cytosol TM proteins inserted contrary to the PIR, allowing energy-conserving reinsertion. We hypothesize that Spf1 and Ste24 both recognize the short, positively charged ER luminal peptides of TM proteins inserted contrary to the PIR, accepting these peptides into their large membrane-spanning, water-filled cavities through interaction with their many interior surface negative charges. While entry was demonstrated for Spf1, no published evidence directly demonstrates substrate entry to the Ste24 cavity, internal access to its zinc metalloprotease (ZMP) site, or active withdrawal of fragments, which may be essential for function. Spf1 and Ste24 comprise a PIR quality control system that is conserved in all eukaryotes and presumably evolved in prokaryotic progenitors as they gained differentiated membrane functions. About 75% of the PIR is imposed by this quality control system, which joins the UPR, ERAD, and autophagy (ER-phagy) in coordinated, overlapping quality control of ER protein function.
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Affiliation(s)
- Donald J. Tipper
- University of Massachusetts Medical School, Worcester, MA, United States
| | - Carol A. Harley
- i3S-Instituto de Investigação e Inovação em Saude, Universidade do Porto, Porto, Portugal
- IBMC-Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal
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12
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He J, Liu K, Wu Y, Zhao C, Yan S, Chen JH, Hu L, Wang D, Zheng F, Wei W, Xu C, Huang C, Liu X, Yao X, Ding L, Fang Z, Tang AH, Fu C. The AAA-ATPase Yta4/ATAD1 interacts with the mitochondrial divisome to inhibit mitochondrial fission. PLoS Biol 2023; 21:e3002247. [PMID: 37590302 PMCID: PMC10465003 DOI: 10.1371/journal.pbio.3002247] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Revised: 08/29/2023] [Accepted: 07/12/2023] [Indexed: 08/19/2023] Open
Abstract
Mitochondria are in a constant balance of fusion and fission. Excessive fission or deficient fusion leads to mitochondrial fragmentation, causing mitochondrial dysfunction and physiological disorders. How the cell prevents excessive fission of mitochondria is not well understood. Here, we report that the fission yeast AAA-ATPase Yta4, which is the homolog of budding yeast Msp1 responsible for clearing mistargeted tail-anchored (TA) proteins on mitochondria, plays a critical role in preventing excessive mitochondrial fission. The absence of Yta4 leads to mild mitochondrial fragmentation in a Dnm1-dependent manner but severe mitochondrial fragmentation upon induction of mitochondrial depolarization. Overexpression of Yta4 delocalizes the receptor proteins of Dnm1, i.e., Fis1 (a TA protein) and Mdv1 (the bridging protein between Fis1 and Dnm1), from mitochondria and reduces the localization of Dnm1 to mitochondria. The effect of Yta4 overexpression on Fis1 and Mdv1, but not Dnm1, depends on the ATPase and translocase activities of Yta4. Moreover, Yta4 interacts with Dnm1, Mdv1, and Fis1. In addition, Yta4 competes with Dnm1 for binding Mdv1 and decreases the affinity of Dnm1 for GTP and inhibits Dnm1 assembly in vitro. These findings suggest a model, in which Yta4 inhibits mitochondrial fission by inhibiting the function of the mitochondrial divisome composed of Fis1, Mdv1, and Dnm1. Therefore, the present work reveals an uncharacterized molecular mechanism underlying the inhibition of mitochondrial fission.
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Affiliation(s)
- Jiajia He
- MOE Key Laboratory for Cellular Dynamics & Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
- Anhui Key Laboratory of Cellular Dynamics and Chemical Biology & Hefei National Research Center for Interdisciplinary Sciences at the Microscale, School of Life Sciences, University of Science and Technology of China, Hefei, China
| | - Ke Liu
- MOE Key Laboratory for Cellular Dynamics & Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
- Anhui Key Laboratory of Cellular Dynamics and Chemical Biology & Hefei National Research Center for Interdisciplinary Sciences at the Microscale, School of Life Sciences, University of Science and Technology of China, Hefei, China
| | - Yifan Wu
- MOE Key Laboratory for Cellular Dynamics & Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
| | - Chenhui Zhao
- MOE Key Laboratory for Cellular Dynamics & Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
| | - Shuaijie Yan
- MOE Key Laboratory for Cellular Dynamics & Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
| | - Jia-Hui Chen
- MOE Key Laboratory for Cellular Dynamics & Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
- Institute of Artificial Intelligence, Hefei Comprehensive National Science Center, Hefei, China
| | - Lizhu Hu
- Anhui Province Key Laboratory of Medical Physics and Technology, Institute of Health and Medical Technology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, China
| | - Dongmei Wang
- MOE Key Laboratory for Cellular Dynamics & Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
| | - Fan Zheng
- MOE Key Laboratory for Cellular Dynamics & Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
| | - Wenfan Wei
- MOE Key Laboratory for Cellular Dynamics & Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
| | - Chao Xu
- MOE Key Laboratory for Cellular Dynamics & Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
- Anhui Key Laboratory of Cellular Dynamics and Chemical Biology & Hefei National Research Center for Interdisciplinary Sciences at the Microscale, School of Life Sciences, University of Science and Technology of China, Hefei, China
| | - Chengdong Huang
- MOE Key Laboratory for Cellular Dynamics & Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
- Anhui Key Laboratory of Cellular Dynamics and Chemical Biology & Hefei National Research Center for Interdisciplinary Sciences at the Microscale, School of Life Sciences, University of Science and Technology of China, Hefei, China
| | - Xing Liu
- MOE Key Laboratory for Cellular Dynamics & Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
- Anhui Key Laboratory of Cellular Dynamics and Chemical Biology & Hefei National Research Center for Interdisciplinary Sciences at the Microscale, School of Life Sciences, University of Science and Technology of China, Hefei, China
| | - Xuebiao Yao
- MOE Key Laboratory for Cellular Dynamics & Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
- Anhui Key Laboratory of Cellular Dynamics and Chemical Biology & Hefei National Research Center for Interdisciplinary Sciences at the Microscale, School of Life Sciences, University of Science and Technology of China, Hefei, China
| | - Lijun Ding
- Center for Reproductive Medicine, Department of Obstetrics and Gynecology, The Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing, China
| | - Zhiyou Fang
- Anhui Province Key Laboratory of Medical Physics and Technology, Institute of Health and Medical Technology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, China
| | - Ai-Hui Tang
- MOE Key Laboratory for Cellular Dynamics & Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
- Institute of Artificial Intelligence, Hefei Comprehensive National Science Center, Hefei, China
| | - Chuanhai Fu
- MOE Key Laboratory for Cellular Dynamics & Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
- Anhui Key Laboratory of Cellular Dynamics and Chemical Biology & Hefei National Research Center for Interdisciplinary Sciences at the Microscale, School of Life Sciences, University of Science and Technology of China, Hefei, China
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13
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Barlow AN, Manu MS, Saladi SM, Tarr PT, Yadav Y, Thinn AMM, Zhu Y, Laganowsky AD, Clemons WM, Ramasamy S. Structures of Get3d reveal a distinct architecture associated with the emergence of photosynthesis. J Biol Chem 2023; 299:104752. [PMID: 37100288 PMCID: PMC10248533 DOI: 10.1016/j.jbc.2023.104752] [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: 02/16/2023] [Revised: 04/16/2023] [Accepted: 04/21/2023] [Indexed: 04/28/2023] Open
Abstract
Homologs of the protein Get3 have been identified in all domains yet remain to be fully characterized. In the eukaryotic cytoplasm, Get3 delivers tail-anchored (TA) integral membrane proteins, defined by a single transmembrane helix at their C terminus, to the endoplasmic reticulum. While most eukaryotes have a single Get3 gene, plants are notable for having multiple Get3 paralogs. Get3d is conserved across land plants and photosynthetic bacteria and includes a distinctive C-terminal α-crystallin domain. After tracing the evolutionary origin of Get3d, we solve the Arabidopsis thaliana Get3d crystal structure, identify its localization to the chloroplast, and provide evidence for a role in TA protein binding. The structure is identical to that of a cyanobacterial Get3 homolog, which is further refined here. Distinct features of Get3d include an incomplete active site, a "closed" conformation in the apo-state, and a hydrophobic chamber. Both homologs have ATPase activity and are capable of binding TA proteins, supporting a potential role in TA protein targeting. Get3d is first found with the development of photosynthesis and conserved across 1.2 billion years into the chloroplasts of higher plants across the evolution of photosynthesis suggesting a role in the homeostasis of photosynthetic machinery.
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Affiliation(s)
- Alexandra N Barlow
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA
| | - M S Manu
- Division of Biochemical Sciences, CSIR-National Chemical Laboratory, Pune, India
| | - Shyam M Saladi
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA
| | - Paul T Tarr
- Howard Hughes Medical Institute and Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California, USA
| | - Yashpal Yadav
- Division of Biochemical Sciences, CSIR-National Chemical Laboratory, Pune, India
| | - Aye M M Thinn
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA
| | - Yun Zhu
- Department of Chemistry, Texas A&M University, College Station, Texas, USA
| | | | - William M Clemons
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA.
| | - Sureshkumar Ramasamy
- Division of Biochemical Sciences, CSIR-National Chemical Laboratory, Pune, India.
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14
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Breeze E, Vale V, McLellan H, Pecrix Y, Godiard L, Grant M, Frigerio L. A tell tail sign: a conserved C-terminal tail-anchor domain targets a subset of pathogen effectors to the plant endoplasmic reticulum. JOURNAL OF EXPERIMENTAL BOTANY 2023; 74:3188-3202. [PMID: 36860200 DOI: 10.1093/jxb/erad075] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2022] [Accepted: 02/27/2023] [Indexed: 05/21/2023]
Abstract
The endoplasmic reticulum (ER) is the entry point to the secretory pathway and, as such, is critical for adaptive responses to biotic stress, when the demand for de novo synthesis of immunity-related proteins and signalling components increases significantly. Successful phytopathogens have evolved an arsenal of small effector proteins which collectively reconfigure multiple host components and signalling pathways to promote virulence; a small, but important, subset of which are targeted to the endomembrane system including the ER. We identified and validated a conserved C-terminal tail-anchor motif in a set of pathogen effectors known to localize to the ER from the oomycetes Hyaloperonospora arabidopsidis and Plasmopara halstedii (downy mildew of Arabidopsis and sunflower, respectively) and used this protein topology to develop a bioinformatic pipeline to identify putative ER-localized effectors within the effectorome of the related oomycete, Phytophthora infestans, the causal agent of potato late blight. Many of the identified P. infestans tail-anchor effectors converged on ER-localized NAC transcription factors, indicating that this family is a critical host target for multiple pathogens.
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Affiliation(s)
- Emily Breeze
- School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK
| | - Victoria Vale
- School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK
| | - Hazel McLellan
- Division of Plant Science, University of Dundee (at JHI), Invergowrie, Dundee DD2 5DA, UK
| | - Yann Pecrix
- CIRAD, UMR PVBMT, Peuplements Végétaux et Bioagresseurs en Milieu Tropical (UMR C53), Ligne Paradis, 97410 St Pierre, La Réunion, France
| | - Laurence Godiard
- Laboratoire des Interactions Plantes Microbes Environnement (LIPME), Institut National de Recherche pour l'Agriculture, l'Alimentation, et l'Environnement (INRAE), Centre National de la Recherche Scientifique (CNRS), Université de Toulouse, Castanet-Tolosan, France
| | - Murray Grant
- School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK
| | - Lorenzo Frigerio
- School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK
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15
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Sim SI, Park E. P5-ATPases: Structure, substrate specificities, and transport mechanisms. Curr Opin Struct Biol 2023; 79:102531. [PMID: 36724561 DOI: 10.1016/j.sbi.2023.102531] [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: 10/03/2022] [Revised: 11/30/2022] [Accepted: 12/19/2022] [Indexed: 02/01/2023]
Abstract
P5A- and P5B- ATPases, or collectively P5-ATPases, are eukaryotic-specific ATP-dependent transporters that are important for the function of the endoplasmic reticulum (ER) and endo-/lysosomes. However, their substrate specificities had remained enigmatic for many years. Recent cryo-electron microscopy (cryo-EM) and biochemical studies of P5-ATPases have revealed their substrate specificities and transport mechanisms, which were found to be markedly different from other members of the P-type ATPase superfamily. The P5A-ATPase extracts mistargeted or mis-inserted transmembrane helices from the ER membrane for protein quality control, while the P5B-ATPases mediate export of polyamines from late endo-/lysosomes into the cytosol. In this review, we discuss the mechanisms of their substrate recognition and transport based on the cryo-EM structures of the yeast and human P5-ATPases. We highlight how structural diversification of the transmembrane domain has enabled the P5-ATPase subfamily to adapt for transport of atypical substrates.
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Affiliation(s)
- Sue Im Sim
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA
| | - Eunyong Park
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA; California Institute for Quantitative Biosciences, University of California, Berkeley, CA 94720, USA.
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16
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Duart G, Elazar A, Weinstein JY, Gadea-Salom L, Ortiz-Mateu J, Fleishman SJ, Mingarro I, Martinez-Gil L. Computational design of BclxL inhibitors that target transmembrane domain interactions. Proc Natl Acad Sci U S A 2023; 120:e2219648120. [PMID: 36881618 PMCID: PMC10089226 DOI: 10.1073/pnas.2219648120] [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: 11/21/2022] [Accepted: 02/03/2023] [Indexed: 03/08/2023] Open
Abstract
Several methods have been developed to explore interactions among water-soluble proteins or regions of proteins. However, techniques to target transmembrane domains (TMDs) have not been examined thoroughly despite their importance. Here, we developed a computational approach to design sequences that specifically modulate protein-protein interactions in the membrane. To illustrate this method, we demonstrated that BclxL can interact with other members of the B cell lymphoma 2 (Bcl2) family through the TMD and that these interactions are required for BclxL control of cell death. Next, we designed sequences that specifically recognize and sequester the TMD of BclxL. Hence, we were able to prevent BclxL intramembrane interactions and cancel its antiapoptotic effect. These results advance our understanding of protein-protein interactions in membranes and provide a means to modulate them. Moreover, the success of our approach may trigger the development of a generation of inhibitors targeting interactions between TMDs.
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Affiliation(s)
- Gerard Duart
- Department of Biochemistry and Molecular Biology, Institut de Biotecnologia i Biomedicina, Universitat de València, Burjassot46100, Spain
| | - Assaf Elazar
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot76100, Israel
| | - Jonathan Y. Weinstein
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot76100, Israel
| | - Laura Gadea-Salom
- Department of Biochemistry and Molecular Biology, Institut de Biotecnologia i Biomedicina, Universitat de València, Burjassot46100, Spain
| | - Juan Ortiz-Mateu
- Department of Biochemistry and Molecular Biology, Institut de Biotecnologia i Biomedicina, Universitat de València, Burjassot46100, Spain
| | - Sarel J. Fleishman
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot76100, Israel
| | - Ismael Mingarro
- Department of Biochemistry and Molecular Biology, Institut de Biotecnologia i Biomedicina, Universitat de València, Burjassot46100, Spain
| | - Luis Martinez-Gil
- Department of Biochemistry and Molecular Biology, Institut de Biotecnologia i Biomedicina, Universitat de València, Burjassot46100, Spain
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17
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McKenna MJ, Shao S. The Endoplasmic Reticulum and the Fidelity of Nascent Protein Localization. Cold Spring Harb Perspect Biol 2023; 15:a041249. [PMID: 36041782 PMCID: PMC9979852 DOI: 10.1101/cshperspect.a041249] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
High-fidelity protein localization is essential to define the identities and functions of different organelles and to maintain cellular homeostasis. Accurate localization of nascent proteins requires specific protein targeting pathways as well as quality control (QC) mechanisms to remove mislocalized proteins. The endoplasmic reticulum (ER) is the first destination for approximately one-third of the eukaryotic proteome and a major site of protein biosynthesis and QC. In mammalian cells, trafficking from the ER provides nascent proteins access to the extracellular space and essentially every cellular membrane and organelle except for mitochondria and possibly peroxisomes. Here, we discuss the biosynthetic mechanisms that deliver nascent proteins to the ER and the QC mechanisms that interface with the ER to correct or degrade mislocalized proteins.
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Affiliation(s)
- Michael J McKenna
- Department of Cell Biology, Harvard Medical School, Blavatnik Institute, Boston, Massachusetts 02115, USA
| | - Sichen Shao
- Department of Cell Biology, Harvard Medical School, Blavatnik Institute, Boston, Massachusetts 02115, USA
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18
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Heo P, Culver JA, Miao J, Pincet F, Mariappan M. The Get1/2 insertase forms a channel to mediate the insertion of tail-anchored proteins into the ER. Cell Rep 2023; 42:111921. [PMID: 36640319 PMCID: PMC9932932 DOI: 10.1016/j.celrep.2022.111921] [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: 05/31/2021] [Revised: 11/07/2022] [Accepted: 12/13/2022] [Indexed: 12/29/2022] Open
Abstract
Tail-anchored (TA) proteins contain a single C-terminal transmembrane domain (TMD) that is captured by the cytosolic Get3 in yeast (TRC40 in humans). Get3 delivers TA proteins to the Get1/2 complex for insertion into the endoplasmic reticulum (ER) membrane. How Get1/2 mediates insertion of TMDs of TA proteins into the membrane is poorly understood. Using bulk fluorescence and microfluidics assays, we show that Get1/2 forms an aqueous channel in reconstituted bilayers. We estimate the channel diameter to be ∼2.5 nm wide, corresponding to the circumference of two Get1/2 complexes. We find that the Get3 binding can seal the Get1/2 channel, which dynamically opens and closes. Our mutation analysis further shows that the Get1/2 channel activity is required to release TA proteins from Get3 for insertion into the membrane. Hence, we propose that the Get1/2 channel functions as an insertase for insertion of TMDs and as a translocase for translocation of C-terminal hydrophilic segments.
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Affiliation(s)
- Paul Heo
- Laboratoire de Physique de l'Ecole Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, 75005 Paris, France; Institute of Psychiatry and Neuroscience of Paris, INSERM U1266, 75014 Paris, France.
| | - Jacob A. Culver
- Department of Cell Biology, Yale School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA,Nanobiology Institute, Yale University West Campus, West Haven, CT 06516, USA
| | - Jennifer Miao
- Department of Cell Biology, Yale School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA,Nanobiology Institute, Yale University West Campus, West Haven, CT 06516, USA
| | - Frederic Pincet
- Laboratoire de Physique de l'Ecole Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, 75005 Paris, France.
| | - Malaiyalam Mariappan
- Department of Cell Biology, Yale School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA; Nanobiology Institute, Yale University West Campus, West Haven, CT 06516, USA.
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19
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Shan SO. Role of Hsp70 in Post-Translational Protein Targeting: Tail-Anchored Membrane Proteins and Beyond. Int J Mol Sci 2023; 24:1170. [PMID: 36674686 PMCID: PMC9866221 DOI: 10.3390/ijms24021170] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2022] [Revised: 01/02/2023] [Accepted: 01/04/2023] [Indexed: 01/11/2023] Open
Abstract
The Hsp70 family of molecular chaperones acts as a central 'hub' in the cell that interacts with numerous newly synthesized proteins to assist in their biogenesis. Apart from its central and well-established role in facilitating protein folding, Hsp70s also act as key decision points in the cellular chaperone network that direct client proteins to distinct biogenesis and quality control pathways. In this paper, we review accumulating data that illustrate a new branch in the Hsp70 network: the post-translational targeting of nascent membrane and organellar proteins to diverse cellular organelles. Work in multiple pathways suggests that Hsp70, via its ability to interact with components of protein targeting and translocation machineries, can initiate elaborate substrate relays in a sophisticated cascade of chaperones, cochaperones, and receptor proteins, and thus provide a mechanism to safeguard and deliver nascent membrane proteins to the correct cellular membrane. We discuss the mechanistic principles gleaned from better-studied Hsp70-dependent targeting pathways and outline the observations and outstanding questions in less well-studied systems.
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Affiliation(s)
- Shu-Ou Shan
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
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20
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Itskanov S, Park E. Mechanism of Protein Translocation by the Sec61 Translocon Complex. Cold Spring Harb Perspect Biol 2023; 15:a041250. [PMID: 35940906 PMCID: PMC9808579 DOI: 10.1101/cshperspect.a041250] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
The endoplasmic reticulum (ER) is a major site for protein synthesis, folding, and maturation in eukaryotic cells, responsible for production of secretory proteins and most integral membrane proteins. The universally conserved protein-conducting channel Sec61 complex mediates core steps in these processes by translocating hydrophilic polypeptide segments of client proteins across the ER membrane and integrating hydrophobic transmembrane segments into the membrane. The Sec61 complex associates with several other molecular machines and enzymes to enable substrate engagement with the channel and coordination of protein translocation with translation, protein folding, and/or post-translational modifications. Recent cryo-electron microscopy and functional studies of these translocon complexes have greatly advanced our mechanistic understanding of Sec61-dependent protein biogenesis at the ER. Here, we will review the current models for how the Sec61 channel performs its functions in coordination with partner complexes.
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Affiliation(s)
- Samuel Itskanov
- Biophysics Graduate Program
- California Institute for Quantitative Biosciences
| | - Eunyong Park
- California Institute for Quantitative Biosciences
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California 94720, USA
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21
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Bonzerato CG, Wojcikiewicz RJH. Bok: real killer or bystander with non-apoptotic roles? Front Cell Dev Biol 2023; 11:1161910. [PMID: 37123400 PMCID: PMC10130511 DOI: 10.3389/fcell.2023.1161910] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2023] [Accepted: 04/05/2023] [Indexed: 05/02/2023] Open
Abstract
Bcl-2-related ovarian killer, Bok, was first labeled "pro-apoptotic" due to its ability to cause cell death when over-expressed. However, it has become apparent that this is not a good name, since Bok is widely expressed in tissues other than ovaries. Further, there is serious doubt as to whether Bok is a real "killer," due to disparities in the ability of over-expressed versus endogenous Bok to trigger apoptosis. In this brief review, we rationalize these disparities and argue that endogenous Bok is very different from the pro-apoptotic, mitochondrial outer membrane permeabilization mediators, Bak and Bax. Instead, Bok is a stable, endoplasmic reticulum-located protein bound to inositol 1,4,5 trisphosphate receptors. From this location, Bok plays a variety of roles, including regulation of endoplasmic reticulum/mitochondria contact sites and mitochondrial dynamics. Therefore, categorizing Bok as a "killer" may well be misleading and instead, endogenous Bok would better be considered an endoplasmic reticulum-located "bystander", with non-apoptotic roles.
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22
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Bonzerato CG, Keller KR, Schulman JJ, Gao X, Szczesniak LM, Wojcikiewicz RJH. Endogenous Bok is stable at the endoplasmic reticulum membrane and does not mediate proteasome inhibitor-induced apoptosis. Front Cell Dev Biol 2022; 10:1094302. [PMID: 36601536 PMCID: PMC9806350 DOI: 10.3389/fcell.2022.1094302] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2022] [Accepted: 12/07/2022] [Indexed: 12/23/2022] Open
Abstract
Controversy surrounds the cellular role of the Bcl-2 family protein Bok. On one hand, it has been shown that all endogenous Bok is bound to inositol 1,4,5-trisphosphate receptors (IP3Rs), while other data suggest that Bok can act as a pro-apoptotic mitochondrial outer membrane permeabilization mediator, apparently kept at very low and non-apoptotic levels by efficient proteasome-mediated degradation. Here we show that 1) endogenous Bok is expressed at readily-detectable levels in key cultured cells (e.g., mouse embryonic fibroblasts and HCT116 cells) and is not constitutively degraded by the proteasome, 2) proteasome inhibitor-induced apoptosis is not mediated by Bok, 3) endogenous Bok expression level is critically dependent on the presence of IP3Rs, 4) endogenous Bok is rapidly degraded by the ubiquitin-proteasome pathway in the absence of IP3Rs at the endoplasmic reticulum membrane, and 5) charged residues in the transmembrane region of Bok affect its stability, ability to interact with Mcl-1, and pro-apoptotic activity when over-expressed. Overall, these data indicate that endogenous Bok levels are not governed by proteasomal activity (except when IP3Rs are deleted) and that while endogenous Bok plays little or no role in apoptotic signaling, exogenous Bok can mediate apoptosis in a manner dependent on its transmembrane domain.
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23
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McKenna MJ, Adams BM, Chu V, Paulo JA, Shao S. ATP13A1 prevents ERAD of folding-competent mislocalized and misoriented proteins. Mol Cell 2022; 82:4277-4289.e10. [PMID: 36283413 PMCID: PMC9675726 DOI: 10.1016/j.molcel.2022.09.035] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2022] [Revised: 08/18/2022] [Accepted: 09/26/2022] [Indexed: 11/18/2022]
Abstract
The biosynthesis of thousands of proteins requires targeting a signal sequence or transmembrane segment (TM) to the endoplasmic reticulum (ER). These hydrophobic ɑ helices must localize to the appropriate cellular membrane and integrate in the correct topology to maintain a high-fidelity proteome. Here, we show that the P5A-ATPase ATP13A1 prevents the accumulation of mislocalized and misoriented proteins, which are eliminated by different ER-associated degradation (ERAD) pathways in mammalian cells. Without ATP13A1, mitochondrial tail-anchored proteins mislocalize to the ER through the ER membrane protein complex and are cleaved by signal peptide peptidase for ERAD. ATP13A1 also facilitates the topogenesis of a subset of proteins with an N-terminal TM or signal sequence that should insert into the ER membrane with a cytosolic N terminus. Without ATP13A1, such proteins accumulate in the wrong orientation and are targeted for ERAD by distinct ubiquitin ligases. Thus, ATP13A1 prevents ERAD of diverse proteins capable of proper folding.
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Affiliation(s)
- Michael J McKenna
- Department of Cell Biology, Harvard Medical School, 240 Longwood Ave., Boston, MA 02115, USA
| | - Benjamin M Adams
- Department of Cell Biology, Harvard Medical School, 240 Longwood Ave., Boston, MA 02115, USA
| | - Vincent Chu
- Department of Cell Biology, Harvard Medical School, 240 Longwood Ave., Boston, MA 02115, USA
| | - Joao A Paulo
- Department of Cell Biology, Harvard Medical School, 240 Longwood Ave., Boston, MA 02115, USA
| | - Sichen Shao
- Department of Cell Biology, Harvard Medical School, 240 Longwood Ave., Boston, MA 02115, USA.
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24
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Arceo XG, Koslover EF, Zid BM, Brown AI. Mitochondrial mRNA localization is governed by translation kinetics and spatial transport. PLoS Comput Biol 2022; 18:e1010413. [PMID: 35984860 PMCID: PMC9432724 DOI: 10.1371/journal.pcbi.1010413] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Revised: 08/31/2022] [Accepted: 07/19/2022] [Indexed: 11/24/2022] Open
Abstract
For many nuclear-encoded mitochondrial genes, mRNA localizes to the mitochondrial surface co-translationally, aided by the association of a mitochondrial targeting sequence (MTS) on the nascent peptide with the mitochondrial import complex. For a subset of these co-translationally localized mRNAs, their localization is dependent on the metabolic state of the cell, while others are constitutively localized. To explore the differences between these two mRNA types we developed a stochastic, quantitative model for MTS-mediated mRNA localization to mitochondria in yeast cells. This model includes translation, applying gene-specific kinetics derived from experimental data; and diffusion in the cytosol. Even though both mRNA types are co-translationally localized we found that the steady state number, or density, of ribosomes along an mRNA was insufficient to differentiate the two mRNA types. Instead, conditionally-localized mRNAs have faster translation kinetics which modulate localization in combination with changes to diffusive search kinetics across metabolic states. Our model also suggests that the MTS requires a maturation time to become competent to bind mitochondria. Our work indicates that yeast cells can regulate mRNA localization to mitochondria by controlling mitochondrial volume fraction (influencing diffusive search times) and gene translation kinetics (adjusting mRNA binding competence) without the need for mRNA-specific binding proteins. These results shed light on both global and gene-specific mechanisms that enable cells to alter mRNA localization in response to changing metabolic conditions.
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Affiliation(s)
- Ximena G. Arceo
- Department of Chemistry & Biochemistry, University of California, San Diego, La Jolla, California, United States of America
| | - Elena F. Koslover
- Department of Physics, University of California, San Diego, La Jolla, California, United States of America
| | - Brian M. Zid
- Department of Chemistry & Biochemistry, University of California, San Diego, La Jolla, California, United States of America
| | - Aidan I. Brown
- Department of Physics, Ryerson University, Toronto, Canada
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25
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Culver JA, Li X, Jordan M, Mariappan M. A second chance for protein targeting/folding: Ubiquitination and deubiquitination of nascent proteins. Bioessays 2022; 44:e2200014. [PMID: 35357021 PMCID: PMC9133216 DOI: 10.1002/bies.202200014] [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: 01/18/2022] [Revised: 03/09/2022] [Accepted: 03/10/2022] [Indexed: 11/07/2022]
Abstract
Molecular chaperones in cells constantly monitor and bind to exposed hydrophobicity in newly synthesized proteins and assist them in folding or targeting to cellular membranes for insertion. However, proteins can be misfolded or mistargeted, which often causes hydrophobic amino acids to be exposed to the aqueous cytosol. Again, chaperones recognize exposed hydrophobicity in these proteins to prevent nonspecific interactions and aggregation, which are harmful to cells. The chaperone-bound misfolded proteins are then decorated with ubiquitin chains denoting them for proteasomal degradation. It remains enigmatic how molecular chaperones can mediate both maturation of nascent proteins and ubiquitination of misfolded proteins solely based on their exposed hydrophobic signals. In this review, we propose a dynamic ubiquitination and deubiquitination model in which ubiquitination of newly synthesized proteins serves as a "fix me" signal for either refolding of soluble proteins or retargeting of membrane proteins with the help of chaperones and deubiquitinases. Such a model would provide additional time for aberrant nascent proteins to fold or route for membrane insertion, thus avoiding excessive protein degradation and saving cellular energy spent on protein synthesis. Also see the video abstract here: https://youtu.be/gkElfmqaKG4.
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Affiliation(s)
- Jacob A. Culver
- Department of Cell Biology, Nanobiology Institute, Yale School of Medicine, Yale West Campus, West Haven, CT 06516, USA
| | - Xia Li
- Department of Cell Biology, Nanobiology Institute, Yale School of Medicine, Yale West Campus, West Haven, CT 06516, USA
| | - Matthew Jordan
- Department of Cell Biology, Nanobiology Institute, Yale School of Medicine, Yale West Campus, West Haven, CT 06516, USA
| | - Malaiyalam Mariappan
- Department of Cell Biology, Nanobiology Institute, Yale School of Medicine, Yale West Campus, West Haven, CT 06516, USA
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26
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Wang L, Toutkoushian H, Belyy V, Kokontis CY, Walter P. Conserved structural elements specialize ATAD1 as a membrane protein extraction machine. eLife 2022; 11:e73941. [PMID: 35550246 PMCID: PMC9273213 DOI: 10.7554/elife.73941] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Accepted: 05/12/2022] [Indexed: 11/13/2022] Open
Abstract
The mitochondrial AAA (ATPase Associated with diverse cellular Activities) protein ATAD1 (in humans; Msp1 in yeast) removes mislocalized membrane proteins, as well as stuck import substrates from the mitochondrial outer membrane, facilitating their re-insertion into their cognate organelles and maintaining mitochondria's protein import capacity. In doing so, it helps to maintain proteostasis in mitochondria. How ATAD1 tackles the energetic challenge to extract hydrophobic membrane proteins from the lipid bilayer and what structural features adapt ATAD1 for its particular function has remained a mystery. Previously, we determined the structure of Msp1 in complex with a peptide substrate (Wang et al., 2020). The structure showed that Msp1's mechanism follows the general principle established for AAA proteins while adopting several structural features that specialize it for its function. Among these features in Msp1 was the utilization of multiple aromatic amino acids to firmly grip the substrate in the central pore. However, it was not clear whether the aromatic nature of these amino acids were required, or if they could be functionally replaced by aliphatic amino acids. In this work, we determined the cryo-EM structures of the human ATAD1 in complex with a peptide substrate at near atomic resolution. The structures show that phylogenetically conserved structural elements adapt ATAD1 for its function while generally adopting a conserved mechanism shared by many AAA proteins. We developed a microscopy-based assay reporting on protein mislocalization, with which we directly assessed ATAD1's activity in live cells and showed that both aromatic amino acids in pore-loop 1 are required for ATAD1's function and cannot be substituted by aliphatic amino acids. A short α-helix at the C-terminus strongly facilitates ATAD1's oligomerization, a structural feature that distinguishes ATAD1 from its closely related proteins.
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Affiliation(s)
- Lan Wang
- Department of Biochemistry and Biophysics, University of California at San FranciscoSan FranciscoUnited States
- Howard Hughes Medical Institute, University of California at San FranciscoSan FranciscoUnited States
| | - Hannah Toutkoushian
- Department of Biochemistry and Biophysics, University of California at San FranciscoSan FranciscoUnited States
- Howard Hughes Medical Institute, University of California at San FranciscoSan FranciscoUnited States
| | - Vladislav Belyy
- Department of Biochemistry and Biophysics, University of California at San FranciscoSan FranciscoUnited States
- Howard Hughes Medical Institute, University of California at San FranciscoSan FranciscoUnited States
| | - Claire Y Kokontis
- Department of Biochemistry and Biophysics, University of California at San FranciscoSan FranciscoUnited States
| | - Peter Walter
- Department of Biochemistry and Biophysics, University of California at San FranciscoSan FranciscoUnited States
- Howard Hughes Medical Institute, University of California at San FranciscoSan FranciscoUnited States
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27
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BAG6 prevents the aggregation of neurodegeneration-associated fragments of TDP43. iScience 2022; 25:104273. [PMID: 35542047 PMCID: PMC9079172 DOI: 10.1016/j.isci.2022.104273] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2021] [Revised: 12/23/2021] [Accepted: 04/14/2022] [Indexed: 11/24/2022] Open
Abstract
Neurodegeneration is associated with the aggregation of proteins bearing solvent-exposed hydrophobicity as a result of their misfolding and/or proteolytic cleavage. An understanding of the cellular protein quality control mechanisms which prevent protein aggregation is fundamental to understanding the etiology of neurodegeneration. By examining the metabolism of disease-linked C-terminal fragments of the TAR DNA-binding protein 43 (TDP43), we found that the Bcl-2 associated athanogene 6 (BAG6) functions as a sensor of proteolytic fragments bearing exposed hydrophobicity and prevents their intracellular aggregation. In addition, BAG6 facilitates the ubiquitylation of TDP43 fragments by recruiting the Ub-ligase, Ring finger protein 126 (RNF126). Authenticating its role in preventing aggregation, we found that TDP43 fragments form intracellular aggregates in the absence of BAG6. Finally, we found that BAG6 could interact with and solubilize additional neurodegeneration-associated proteolytic fragments. Therefore, BAG6 plays a general role in preventing intracellular aggregation associated with neurodegeneration. Proteolytic cleavage generates protein fragments bearing exposed hydrophobicity BAG6 maintains the solubility and directs the degradation of protein fragments BAG6 prevents intracellular aggregation associated with neurodegeneration
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28
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Giska F, Mariappan M, Bhattacharyya M, Gupta K. Deciphering the molecular organization of GET pathway chaperones through native mass spectrometry. Biophys J 2022; 121:1289-1298. [PMID: 35189106 PMCID: PMC9034188 DOI: 10.1016/j.bpj.2022.02.026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2021] [Revised: 10/25/2021] [Accepted: 02/15/2022] [Indexed: 11/02/2022] Open
Abstract
Get3/4/5 chaperone complex is responsible for targeting C-terminal tail-anchored membrane proteins to the endoplasmic reticulum. Despite the availability of several crystal structures of independent proteins and partial structures of subcomplexes, different models of oligomeric states and structural organization have been proposed for the protein complexes involved. Here, using native mass spectrometry (Native-MS), coupled with intact dissociation, we show that Get4/5 exclusively forms a tetramer using both Get5/5 and a novel Get4/4 dimerization interface. Addition of Get3 to this leads to a hexameric (Get3)2-(Get4)2-(Get5)2 complex with closed-ring cyclic architecture. We further validate our claims through molecular modeling and mutational abrogation of the proposed interfaces. Native-MS has become a principal tool to determine the state of oligomeric organization of proteins. The work demonstrates that for multiprotein complexes, native-MS, coupled with molecular modeling and mutational perturbation, can provide an alternative route to render a detailed view of both the oligomeric states as well as the molecular interfaces involved. This is especially useful for large multiprotein complexes with large unstructured domains that make it recalcitrant to conventional structure determination approaches.
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Affiliation(s)
- Fabian Giska
- Department of Cell Biology, Yale School of Medicine, New Haven, Connecticut; Nanobiology Institute, Yale University, West Haven, Connecticut
| | - Malaiyalam Mariappan
- Department of Cell Biology, Yale School of Medicine, New Haven, Connecticut; Nanobiology Institute, Yale University, West Haven, Connecticut
| | | | - Kallol Gupta
- Department of Cell Biology, Yale School of Medicine, New Haven, Connecticut; Nanobiology Institute, Yale University, West Haven, Connecticut.
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29
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Abstract
The endoplasmic reticulum (ER) is the site of membrane protein insertion, folding, and assembly in eukaryotes. Over the past few years, a combination of genetic and biochemical studies have implicated an abundant factor termed the ER membrane protein complex (EMC) in several aspects of membrane protein biogenesis. This large nine-protein complex is built around a deeply conserved core formed by the EMC3-EMC6 subcomplex. EMC3 belongs to the universally conserved Oxa1 superfamily of membrane protein transporters, whereas EMC6 is an ancient, widely conserved obligate partner. EMC has an established role in the insertion of transmembrane domains (TMDs) and less understood roles during the later steps of membrane protein folding and assembly. Several recent structures suggest hypotheses about the mechanism(s) of TMD insertion by EMC, with various biochemical and proteomics studies beginning to reveal the range of EMC's membrane protein substrates. Expected final online publication date for the Annual Review of Biochemistry, Volume 91 is June 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Affiliation(s)
- Ramanujan S Hegde
- Medical Research Council Laboratory of Molecular Biology, Cambridge, United Kingdom;
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30
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Abstract
Junctophilins (JPHs) comprise a family of structural proteins that connect the plasma membrane to intracellular organelles such as the endo/sarcoplasmic reticulum. Tethering of these membrane structures results in the formation of highly organized subcellular junctions that play important signaling roles in all excitable cell types. There are four JPH isoforms, expressed primarily in muscle and neuronal cell types. Each JPH protein consists of 6 'membrane occupation and recognition nexus' (MORN) motifs, a joining region connecting these to another set of 2 MORN motifs, a putative alpha-helical region, a divergent region exhibiting low homology between JPH isoforms, and a carboxy-terminal transmembrane region anchoring into the ER/SR membrane. JPH isoforms play essential roles in developing and maintaining subcellular membrane junctions. Conversely, inherited mutations in JPH2 cause hypertrophic or dilated cardiomyopathy, while trinucleotide expansions in the JPH3 gene cause Huntington Disease-Like 2. Loss of JPH1 protein levels can cause skeletal myopathy, while loss of cardiac JPH2 levels causes heart failure and atrial fibrillation, among other disease. This review will provide a comprehensive overview of the JPH gene family, phylogeny, and evolutionary analysis of JPH genes and other MORN domain proteins. JPH biogenesis, membrane tethering, and binding partners will be discussed, as well as functional roles of JPH isoforms in excitable cells. Finally, potential roles of JPH isoform deficits in human disease pathogenesis will be reviewed.
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Affiliation(s)
- Stephan E Lehnart
- Cellular Biophysics and Translational Cardiology Section, Heart Research Center Göttingen, University Medical Center Göttingen, Department of Cardiology and Pneumology, Georg-August University Göttingen, Göttingen, Germany.,Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Göttingen, Germany.,DZHK (German Centre for Cardiovascular Research), partner site Göttingen, Germany
| | - Xander H T Wehrens
- Cardiovascular Research Institute, Baylor College of Medicine, Houston, Texas, United States; Departments of Molecular Physiology and Biophysics, Medicine (Cardiology), Pediatrics (Cardiology), Neuroscience, and Center for Space Medicine, Baylor College of Medicine, Houston, Texas, United States
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31
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Mehlhorn DG, Asseck LY, Grefen C. Looking for a safe haven: tail-anchored proteins and their membrane insertion pathways. PLANT PHYSIOLOGY 2021; 187:1916-1928. [PMID: 35235667 PMCID: PMC8644595 DOI: 10.1093/plphys/kiab298] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2021] [Accepted: 06/05/2021] [Indexed: 06/14/2023]
Abstract
Insertion of membrane proteins into the lipid bilayer is a crucial step during their biosynthesis. Eukaryotic cells face many challenges in directing these proteins to their predestined target membrane. The hydrophobic signal peptide or transmembrane domain (TMD) of the nascent protein must be shielded from the aqueous cytosol and its target membrane identified followed by transport and insertion. Components that evolved to deal with each of these challenging steps range from chaperones to receptors, insertases, and sophisticated translocation complexes. One prominent translocation pathway for most proteins is the signal recognition particle (SRP)-dependent pathway which mediates co-translational translocation of proteins across or into the endoplasmic reticulum (ER) membrane. This textbook example of protein insertion is stretched to its limits when faced with secretory or membrane proteins that lack an amino-terminal signal sequence or TMD. Particularly, a large group of so-called tail-anchored (TA) proteins that harbor a single carboxy-terminal TMD require an alternative, post-translational insertion route into the ER membrane. In this review, we summarize the current research in TA protein insertion with a special focus on plants, address challenges, and highlight future research avenues.
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Affiliation(s)
- Dietmar G Mehlhorn
- Faculty of Biology and Biotechnology, Molecular and Cellular Botany, University of Bochum, Universitätsstraße 150, 44780 Bochum, Germany
| | - Lisa Y Asseck
- Faculty of Biology and Biotechnology, Molecular and Cellular Botany, University of Bochum, Universitätsstraße 150, 44780 Bochum, Germany
| | - Christopher Grefen
- Faculty of Biology and Biotechnology, Molecular and Cellular Botany, University of Bochum, Universitätsstraße 150, 44780 Bochum, Germany
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32
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Keszei AF, Yip MC, Hsieh TC, Shao S. Structural insights into metazoan pretargeting GET complexes. Nat Struct Mol Biol 2021; 28:1029-1037. [PMID: 34887561 PMCID: PMC9477564 DOI: 10.1038/s41594-021-00690-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2021] [Accepted: 10/20/2021] [Indexed: 11/09/2022]
Abstract
Close coordination between chaperones is essential for protein biosynthesis, including the delivery of tail-anchored (TA) proteins containing a single C-terminal transmembrane domain to the endoplasmic reticulum (ER) by the conserved GET pathway. For successful targeting, nascent TA proteins must be promptly chaperoned and loaded onto the cytosolic ATPase Get3 through a transfer reaction involving the chaperone SGTA and bridging factors Get4, Ubl4a and Bag6. Here, we report cryo-electron microscopy structures of metazoan pretargeting GET complexes at 3.3-3.6 Å. The structures reveal that Get3 helix 8 and the Get4 C terminus form a composite lid over the Get3 substrate-binding chamber that is opened by SGTA. Another interaction with Get4 prevents formation of Get3 helix 4, which links the substrate chamber and ATPase domain. Both interactions facilitate TA protein transfer from SGTA to Get3. Our findings show how the pretargeting complex primes Get3 for coordinated client loading and ER targeting.
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Affiliation(s)
- Alexander F.A. Keszei
- Department of Cell Biology, Harvard Medical School, Blavatnik Institute, 240 Longwood Ave., Boston, MA 02115
| | - Matthew C.J. Yip
- Department of Cell Biology, Harvard Medical School, Blavatnik Institute, 240 Longwood Ave., Boston, MA 02115
| | - Ta-Chien Hsieh
- Department of Cell Biology, Harvard Medical School, Blavatnik Institute, 240 Longwood Ave., Boston, MA 02115,Massachusetts College of Pharmacy and Health Sciences, 179 Longwood Ave., Boston, MA 02115
| | - Sichen Shao
- Department of Cell Biology, Harvard Medical School, Blavatnik Institute, Boston, MA, USA.
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33
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Kumar T, Maitra S, Rahman A, Bhattacharjee S. A conserved guided entry of tail-anchored pathway is involved in the trafficking of a subset of membrane proteins in Plasmodium falciparum. PLoS Pathog 2021; 17:e1009595. [PMID: 34780541 PMCID: PMC8629386 DOI: 10.1371/journal.ppat.1009595] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Revised: 11/29/2021] [Accepted: 10/19/2021] [Indexed: 01/22/2023] Open
Abstract
Tail-anchored (TA) proteins are defined by the absence of N-terminus signal sequence and the presence of a single transmembrane domain (TMD) proximal to their C-terminus. They play fundamental roles in cellular processes including vesicular trafficking, protein translocation and quality control. Some of the TA proteins are post-translationally integrated by the Guided Entry of TA (GET) pathway to the cellular membranes; with their N-terminus oriented towards the cytosol and C-terminus facing the organellar lumen. The TA repertoire and the GET machinery have been extensively characterized in the yeast and mammalian systems, however, they remain elusive in the human malaria parasite Plasmodium falciparum. In this study, we bioinformatically predicted a total of 63 TA proteins in the P. falciparum proteome and revealed the association of a subset with the P. falciparum homolog of Get3 (PfGet3). In addition, our proximity labelling studies either definitively identified or shortlisted the other eligible GET constituents, and our in vitro association studies validated associations between PfGet3 and the corresponding homologs of Get4 and Get2 in P. falciparum. Collectively, this study reveals the presence of proteins with hallmark TA signatures and the involvement of evolutionary conserved GET trafficking pathway for their targeted delivery within the parasite. Tail-anchored (TA) membrane proteins are known to play essential cellular functions in the eukaryotes. These proteins are trafficked to their respective destinations by post-translational translocation pathways that are evolutionarily conserved from yeast to human. However, they remain unidentified in the malaria parasite Plasmodium falciparum. We have used bioinformatic prediction algorithms in conjunction with functional validation studies to identify the candidate TA repertoire and some of the homologs of the trafficking machinery in P. falciparum. Initially, we predicted the presence of 63 putative TA proteins localized to distinct compartments within this parasite, including a few confirmed TA homologs in other eukaryotic systems. We then identified and characterized PfGet3 as a central component in the Guided-Entry of TA (GET) translocation machinery, and our bacterial co-expression and pulldown assays with two selected recombinant TA proteins, PfBOS1 and PfUSE1, showed co-association with PfGet3. We also identified PfGet2 and PfGet4 as the other two components of the GET machinery in P. falciparum using proximity biotinylation followed by mass spectrometry. Interestingly, we also found six TA proteins in the parasite enriched in this fraction. We further validated the direct interactions between a few TA candidates, PfGet4 and PfGet2 with PfGet3 using recombinant-based pulldown studies. In conclusion, this study classified a subset of membrane proteins with the TA nomenclature and implicated a previously unidentified GET pathway for their translocation in this apicomplexan parasite.
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Affiliation(s)
- Tarkeshwar Kumar
- Special Centre for Molecular Medicine, Jawaharlal Nehru University, New Delhi, India
| | - Satarupa Maitra
- Special Centre for Molecular Medicine, Jawaharlal Nehru University, New Delhi, India
| | - Abdur Rahman
- Special Centre for Molecular Medicine, Jawaharlal Nehru University, New Delhi, India
| | - Souvik Bhattacharjee
- Special Centre for Molecular Medicine, Jawaharlal Nehru University, New Delhi, India
- * E-mail:
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34
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Chio US, Liu Y, Chung S, Shim WJ, Chandrasekar S, Weiss S, Shan SO. Subunit cooperation in the Get1/2 receptor promotes tail-anchored membrane protein insertion. J Cell Biol 2021; 220:212681. [PMID: 34614151 PMCID: PMC8530227 DOI: 10.1083/jcb.202103079] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Revised: 08/03/2021] [Accepted: 08/19/2021] [Indexed: 11/29/2022] Open
Abstract
The guided entry of tail-anchored protein (GET) pathway, in which the Get3 ATPase delivers an essential class of tail-anchored membrane proteins (TAs) to the Get1/2 receptor at the endoplasmic reticulum, provides a conserved mechanism for TA biogenesis in eukaryotic cells. The membrane-associated events of this pathway remain poorly understood. Here we show that complex assembly between the cytosolic domains (CDs) of Get1 and Get2 strongly enhances the affinity of the individual subunits for Get3•TA, thus enabling efficient capture of the targeting complex. In addition to the known role of Get1CD in remodeling Get3 conformation, two molecular recognition features (MoRFs) in Get2CD induce Get3 opening, and both subunits are required for optimal TA release from Get3. Mutation of the MoRFs attenuates TA insertion into the ER in vivo. Our results demonstrate extensive cooperation between the Get1/2 receptor subunits in the capture and remodeling of the targeting complex, and emphasize the role of MoRFs in receptor function during membrane protein biogenesis.
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Affiliation(s)
- Un Seng Chio
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA
| | - Yumeng Liu
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA
| | - SangYoon Chung
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA
| | - Woo Jun Shim
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA
| | - Sowmya Chandrasekar
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA
| | - Shimon Weiss
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA.,Department of Physics, Institute for Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan, Israel
| | - Shu-Ou Shan
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA
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35
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Mentrup T, Schröder B. Signal peptide peptidase-like 2 proteases: Regulatory switches or proteasome of the membrane? BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2021; 1869:119163. [PMID: 34673079 DOI: 10.1016/j.bbamcr.2021.119163] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Revised: 10/07/2021] [Accepted: 10/11/2021] [Indexed: 12/30/2022]
Abstract
Signal peptide peptidase-like 2 (SPPL) proteases constitute a subfamily of SPP/SPPL intramembrane proteases which are homologues of the presenilins, the catalytic core of the γ-secretase complex. The three SPPL2 proteases SPPL2a, SPPL2b and SPPL2c proteolyse single-span, type II-oriented transmembrane proteins and/or tail-anchored proteins within their hydrophobic transmembrane segments. We review recent progress in defining substrate spectra and in vivo functions of these proteases. Characterisation of the respective knockout mice has implicated SPPL2 proteases in immune cell differentiation and function, prevention of atherosclerotic plaque development and spermatogenesis. Mechanisms how substrates are selected by these enzymes are still incompletely understood. We will discuss current views on how selective SPPL2-mediated cleavage is or whether these proteases may exhibit a generalised role in the turnover of membrane proteins. This has been suggested previously for the mechanistically related γ-secretase for which the term "proteasome of the membrane" has been coined based on its broad substrate spectrum. With regard to individual substrates, potential signalling functions of the resulting cytosolic cleavage fragments remain a controversial aspect. However, it has been clearly shown that SPPL2 proteases can influence cellular signalling and membrane trafficking by controlling levels of their membrane-bound substrate proteins which highlights these enzymes as regulatory switches. Based on this, regulatory mechanisms controlling activity of SPPL2 proteases would need to be postulated, which are just beginning to emerge. These different questions, which are relevant for other families of intramembrane proteases in a similar way, will be critically discussed based on the current state of knowledge.
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Affiliation(s)
- Torben Mentrup
- Institute for Physiological Chemistry, Technische Universität Dresden, Fiedlerstraße 42, D-01307 Dresden, Germany
| | - Bernd Schröder
- Institute for Physiological Chemistry, Technische Universität Dresden, Fiedlerstraße 42, D-01307 Dresden, Germany.
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36
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Fry MY, Saladi SM, Cunha A, Clemons WM. Sequence-based features that are determinant for tail-anchored membrane protein sorting in eukaryotes. Traffic 2021; 22:306-318. [PMID: 34288289 PMCID: PMC8380732 DOI: 10.1111/tra.12809] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Revised: 07/15/2021] [Accepted: 07/18/2021] [Indexed: 11/29/2022]
Abstract
The correct targeting and insertion of tail-anchored (TA) integral membrane proteins is critical for cellular homeostasis. TA proteins are defined by a hydrophobic transmembrane domain (TMD) at their C-terminus and are targeted to either the ER or mitochondria. Derived from experimental measurements of a few TA proteins, there has been little examination of the TMD features that determine localization. As a result, the localization of many TA proteins are misclassified by the simple heuristic of overall hydrophobicity. Because ER-directed TMDs favor arrangement of hydrophobic residues to one side, we sought to explore the role of geometric hydrophobic properties. By curating TA proteins with experimentally determined localizations and assessing hypotheses for recognition, we bioinformatically and experimentally verify that a hydrophobic face is the most accurate singular metric for separating ER and mitochondria-destined yeast TA proteins. A metric focusing on an 11 residue segment of the TMD performs well when classifying human TA proteins. The most inclusive predictor uses both hydrophobicity and C-terminal charge in tandem. This work provides context for previous observations and opens the door for more detailed mechanistic experiments to determine the molecular factors driving this recognition.
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Affiliation(s)
- Michelle Y. Fry
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA
| | - Shyam M. Saladi
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA
| | - Alexandre Cunha
- Division of Biology and Biological Engineering, Center for Advanced Methods in Biological Image Analysis, Beckman Institute, Pasadena, California, USA
| | - William M. Clemons
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA
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37
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Anderson SA, Satyanarayan MB, Wessendorf RL, Lu Y, Fernandez DE. A homolog of GuidedEntry of Tail-anchored proteins3 functions in membrane-specific protein targeting in chloroplasts of Arabidopsis. THE PLANT CELL 2021; 33:2812-2833. [PMID: 34021351 PMCID: PMC8408437 DOI: 10.1093/plcell/koab145] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Accepted: 05/18/2021] [Indexed: 05/12/2023]
Abstract
The chloroplasts and mitochondria of photosynthetic eukaryotes contain proteins that are closely related to cytosolic Guided Entry of Tail-anchored proteins3 (Get3). Get3 is a targeting factor that efficiently escorts tail-anchored (TA) proteins to the ER. Because other components of the cytosolic-targeting pathway appear to be absent in organelles, previous investigators have asserted that organellar Get3 homologs are unlikely to act as targeting factors. However, we show here both that the Arabidopsis thaliana chloroplast homolog designated as GET3B is structurally similar to cytosolic Get3 proteins and that it selectively binds a thylakoid-localized TA protein. Based on genetic interactions between a get3b mutation and mutations affecting the chloroplast signal recognition particle-targeting pathway, as well as changes in the abundance of photosynthesis-related proteins in mutant plants, we propose that GET3B acts primarily to direct proteins to the thylakoids. Furthermore, through molecular complementation experiments, we show that function of GET3B depends on its ability to hydrolyze ATP, and this is consistent with action as a targeting factor. We propose that GET3B and related organellar Get3 homologs play a role that is analogous to that of cytosolic Get3 proteins, and that GET3B acts as a targeting factor in the chloroplast stroma to deliver TA proteins in a membrane-specific manner.
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Affiliation(s)
- Stacy A. Anderson
- Department of Botany, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - Manasa B. Satyanarayan
- Department of Biological Sciences, Western Michigan University, Kalamazoo, Michigan 49008, USA
| | - Ryan L. Wessendorf
- Department of Biological Sciences, Western Michigan University, Kalamazoo, Michigan 49008, USA
| | - Yan Lu
- Department of Biological Sciences, Western Michigan University, Kalamazoo, Michigan 49008, USA
| | - Donna E. Fernandez
- Department of Botany, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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38
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Farkas Á, Bohnsack KE. Capture and delivery of tail-anchored proteins to the endoplasmic reticulum. J Cell Biol 2021; 220:212470. [PMID: 34264263 PMCID: PMC8287540 DOI: 10.1083/jcb.202105004] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2021] [Revised: 06/20/2021] [Accepted: 06/22/2021] [Indexed: 11/22/2022] Open
Abstract
Tail-anchored (TA) proteins fulfill diverse cellular functions within different organellar membranes. Their characteristic C-terminal transmembrane segment renders TA proteins inherently prone to aggregation and necessitates their posttranslational targeting. The guided entry of TA proteins (GET in yeast)/transmembrane recognition complex (TRC in humans) pathway represents a major route for TA proteins to the endoplasmic reticulum (ER). Here, we review important new insights into the capture of nascent TA proteins at the ribosome by the GET pathway pretargeting complex and the mechanism of their delivery into the ER membrane by the GET receptor insertase. Interestingly, several alternative routes by which TA proteins can be targeted to the ER have emerged, raising intriguing questions about how selectivity is achieved during TA protein capture. Furthermore, mistargeting of TA proteins is a fundamental cellular problem, and we discuss the recently discovered quality control machineries in the ER and outer mitochondrial membrane for displacing mislocalized TA proteins.
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Affiliation(s)
- Ákos Farkas
- Department of Molecular Biology, University Medical Center Göttingen, Göttingen, Germany
| | - Katherine E Bohnsack
- Department of Molecular Biology, University Medical Center Göttingen, Göttingen, Germany
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39
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Bentebbal SA, Meqbel BR, Salter A, Allan V, Burke B, Horn HF. A human infertility-associated KASH5 variant promotes mitochondrial localization. Sci Rep 2021; 11:10133. [PMID: 33980926 PMCID: PMC8115505 DOI: 10.1038/s41598-021-89439-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Accepted: 04/22/2021] [Indexed: 02/03/2023] Open
Abstract
KASH5 is the most recently identified member of the KASH domain family of tail anchored, outer nuclear membrane (ONM) and endoplasmic reticulum (ER) proteins. During meiosis prophase I, KASH5 and SUN1 form a complex that spans the nuclear envelope and which links the telomeres of meiotic chromosomes to cytoplasmic dynein. This connection is essential for homologous chromosome dynamics and pairing. A recent study identified a variant in human KASH5 (L535Q) that correlated with male infertility associated with azoospermia. However, no molecular mechanism was described. Here, we report that this amino acid substitution, within the KASH5 transmembrane domain (TMD) has no predicted effects on secondary structure. However, the overall hydrophobicity of the L535Q TMD, is calculated to be lower than the wild-type KASH5, based on the GES (Goldman-Engelman-Steitz) amino acid hydrophobicity scale. This change in hydrophobicity profoundly affects the subcellular localization of KASH5. Through a series of amino acid substitution studies, we show that the L535Q substitution perturbs KASH5 localization to the ER and ONM and instead results in mistargeting to the mitochondria membrane. We suggest that this mislocalization accounts for the infertility and azoospermia phenotype in patients.
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Affiliation(s)
- Sana A. Bentebbal
- grid.452146.00000 0004 1789 3191College of Health and Life Sciences, Hamad Bin Khalifa University, Doha, Qatar
| | - Bakhita R. Meqbel
- grid.452146.00000 0004 1789 3191College of Health and Life Sciences, Hamad Bin Khalifa University, Doha, Qatar
| | - Anna Salter
- grid.5379.80000000121662407Faculty of Life Sciences, University of Manchester, Manchester, M13 9PT UK ,grid.185448.40000 0004 0637 0221Laboratory of Nuclear Dynamics and Architecture, Institute of Medical Biology, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Victoria Allan
- grid.5379.80000000121662407Faculty of Life Sciences, University of Manchester, Manchester, M13 9PT UK
| | - Brian Burke
- grid.185448.40000 0004 0637 0221Laboratory of Nuclear Dynamics and Architecture, Institute of Medical Biology, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Henning F. Horn
- grid.452146.00000 0004 1789 3191College of Health and Life Sciences, Hamad Bin Khalifa University, Doha, Qatar
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40
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McQuown AJ, Reif D, Denic V. A TRCky TA protein delivery service snubs the UPS. J Cell Biol 2021; 220:e202103196. [PMID: 33877288 PMCID: PMC8059096 DOI: 10.1083/jcb.202103196] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
In mammals, tail-anchored (TA) proteins that are posttranslationally captured by the chaperone SGTA are triaged by the BAG6 complex into one of two fates: handoff to an ER targeting factor for membrane insertion or polyubiquitination for destruction by the proteasome. In this issue, Culver and Mariappan (2021. J. Cell Biol.https://doi.org/10.1083/jcb.202004086) show that a fraction of newly synthesized TA proteins is polyubiquitinated in HEK293 cells independently of the BAG6 complex yet evades proteasomal degradation by undergoing deubiquitination en route to becoming stably inserted into the ER membrane.
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Affiliation(s)
| | | | - Vladimir Denic
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA
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41
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Culver JA, Mariappan M. Deubiquitinases USP20/33 promote the biogenesis of tail-anchored membrane proteins. J Cell Biol 2021; 220:211933. [PMID: 33792613 PMCID: PMC8020466 DOI: 10.1083/jcb.202004086] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2020] [Revised: 12/19/2020] [Accepted: 02/24/2021] [Indexed: 12/12/2022] Open
Abstract
Numerous proteins that have hydrophobic transmembrane domains (TMDs) traverse the cytosol and posttranslationally insert into cellular membranes. It is unclear how these hydrophobic membrane proteins evade recognition by the cytosolic protein quality control (PQC), which typically recognizes exposed hydrophobicity in misfolded proteins and marks them for proteasomal degradation by adding ubiquitin chains. Here, we find that tail-anchored (TA) proteins, a vital class of membrane proteins, are recognized by cytosolic PQC and are ubiquitinated as soon as they are synthesized in cells. Surprisingly, the ubiquitinated TA proteins are not routed for proteasomal degradation but instead are handed over to the targeting factor, TRC40, and delivered to the ER for insertion. The ER-associated deubiquitinases, USP20 and USP33, remove ubiquitin chains from TA proteins after their insertion into the ER. Thus, our data suggest that deubiquitinases rescue posttranslationally targeted membrane proteins that are inappropriately ubiquitinated by PQC in the cytosol.
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Affiliation(s)
- Jacob A Culver
- Department of Cell Biology, Nanobiology Institute, Yale School of Medicine, West Haven, CT
| | - Malaiyalam Mariappan
- Department of Cell Biology, Nanobiology Institute, Yale School of Medicine, West Haven, CT
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42
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Cho H, Shim WJ, Liu Y, Shan SO. J-domain proteins promote client relay from Hsp70 during tail-anchored membrane protein targeting. J Biol Chem 2021; 296:100546. [PMID: 33741343 PMCID: PMC8054193 DOI: 10.1016/j.jbc.2021.100546] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2021] [Revised: 02/22/2021] [Accepted: 03/15/2021] [Indexed: 01/17/2023] Open
Abstract
J-domain proteins (JDPs) play essential roles in Hsp70 function by assisting Hsp70 in client trapping and regulating the Hsp70 ATPase cycle. Here, we report that JDPs can further enhance the targeting competence of Hsp70-bound client proteins during tail-anchored protein (TA) biogenesis. In the guided-entry-of-tail-anchored protein pathway in yeast, nascent TAs are captured by cytosolic Hsp70 and sequentially relayed to downstream chaperones, Sgt2 and Get3, for delivery to the ER. We found that two JDPs, Ydj1 and Sis1, function in parallel to support TA targeting to the ER in vivo. Biochemical analyses showed that, while Ydj1 and Sis1 differ in their ability to assist Hsp70 in TA trapping, both JDPs enhance the transfer of Hsp70-bound TAs to Sgt2. The ability of the JDPs to regulate the ATPase cycle of Hsp70 is essential for enhancing the transfer competence of Hsp70-bound TAs in vitro and for supporting TA insertion in vivo. These results demonstrate a role of JDPs in regulating the conformation of Hsp70-bound clients during membrane protein biogenesis.
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Affiliation(s)
- Hyunju Cho
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA
| | - Woo Jun Shim
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA
| | - Yumeng Liu
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA
| | - Shu-Ou Shan
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA.
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43
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Endoplasmic reticulum composition and form: Proteins in and out. Curr Opin Cell Biol 2021; 71:1-6. [PMID: 33611096 DOI: 10.1016/j.ceb.2021.01.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2020] [Revised: 01/18/2021] [Accepted: 01/19/2021] [Indexed: 02/07/2023]
Abstract
The endoplasmic reticulum (ER) is the main harbor for newly synthesized proteins in eukaryotic cells. Through a continuous membrane network of sheets and tubules, the ER hosts secretory proteins, integral membrane proteins, and luminal proteins of the endomembrane system. These proteins are translated by ribosomes outside the ER and require subsequent integration into or translocation across the lipid bilayer of the ER. They are then modified post-translationally and folded in the ER. Some of these proteins are packaged into coat protein complex II-coated vesicles for export. Here, we review recent advances in understanding the mechanism of protein translocation and transmembrane domain insertion in the ER, summarize new insights into selective cargo packaging, and discuss the roles of ER morphological dynamics in these processes.
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44
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Zhang Y, De Laurentiis E, Bohnsack KE, Wahlig M, Ranjan N, Gruseck S, Hackert P, Wölfle T, Rodnina MV, Schwappach B, Rospert S. Ribosome-bound Get4/5 facilitates the capture of tail-anchored proteins by Sgt2 in yeast. Nat Commun 2021; 12:782. [PMID: 33542241 PMCID: PMC7862611 DOI: 10.1038/s41467-021-20981-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2020] [Accepted: 01/05/2021] [Indexed: 02/03/2023] Open
Abstract
The guided entry of tail-anchored proteins (GET) pathway assists in the posttranslational delivery of tail-anchored proteins, containing a single C-terminal transmembrane domain, to the ER. Here we uncover how the yeast GET pathway component Get4/5 facilitates capture of tail-anchored proteins by Sgt2, which interacts with tail-anchors and hands them over to the targeting component Get3. Get4/5 binds directly and with high affinity to ribosomes, positions Sgt2 close to the ribosomal tunnel exit, and facilitates the capture of tail-anchored proteins by Sgt2. The contact sites of Get4/5 on the ribosome overlap with those of SRP, the factor mediating cotranslational ER-targeting. Exposure of internal transmembrane domains at the tunnel exit induces high-affinity ribosome binding of SRP, which in turn prevents ribosome binding of Get4/5. In this way, the position of a transmembrane domain within nascent ER-targeted proteins mediates partitioning into either the GET or SRP pathway directly at the ribosomal tunnel exit. The guided entry of tail-anchored proteins (GET) pathway assists in the delivery of such proteins to the ER. Here, the authors reveal that the pathway components Get4/5 probe a region near the ribosomal exit tunnel. Upon emergence of a client protein, Get4/5 recruits Sgt2 and initiates the targeting phase of the pathway.
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Affiliation(s)
- Ying Zhang
- Institute of Biochemistry and Molecular Biology, University of Freiburg, Freiburg, Germany.,BIOSS Centre for Biological Signaling Studies, University of Freiburg, Freiburg, Germany
| | - Evelina De Laurentiis
- Department of Molecular Biology, University Medical Center Göttingen, Göttingen, Germany.,Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), Göttingen, Germany
| | - Katherine E Bohnsack
- Department of Molecular Biology, University Medical Center Göttingen, Göttingen, Germany
| | - Mascha Wahlig
- Institute of Biochemistry and Molecular Biology, University of Freiburg, Freiburg, Germany.,BIOSS Centre for Biological Signaling Studies, University of Freiburg, Freiburg, Germany
| | - Namit Ranjan
- Max-Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Simon Gruseck
- Institute of Biochemistry and Molecular Biology, University of Freiburg, Freiburg, Germany.,BIOSS Centre for Biological Signaling Studies, University of Freiburg, Freiburg, Germany
| | - Philipp Hackert
- Department of Molecular Biology, University Medical Center Göttingen, Göttingen, Germany
| | - Tina Wölfle
- Institute of Biochemistry and Molecular Biology, University of Freiburg, Freiburg, Germany.,BIOSS Centre for Biological Signaling Studies, University of Freiburg, Freiburg, Germany
| | - Marina V Rodnina
- Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), Göttingen, Germany.,Max-Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Blanche Schwappach
- Department of Molecular Biology, University Medical Center Göttingen, Göttingen, Germany. .,Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), Göttingen, Germany.
| | - Sabine Rospert
- Institute of Biochemistry and Molecular Biology, University of Freiburg, Freiburg, Germany. .,BIOSS Centre for Biological Signaling Studies, University of Freiburg, Freiburg, Germany.
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45
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Wang L, Ye Y. Clearing Traffic Jams During Protein Translocation Across Membranes. Front Cell Dev Biol 2021; 8:610689. [PMID: 33490075 PMCID: PMC7820333 DOI: 10.3389/fcell.2020.610689] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2020] [Accepted: 11/27/2020] [Indexed: 11/13/2022] Open
Abstract
Protein translocation across membranes is a critical facet of protein biogenesis in compartmentalized cells as proteins synthesized in the cytoplasm often need to traverse across lipid bilayers via proteinaceous channels to reach their final destinations. It is well established that protein biogenesis is tightly linked to various protein quality control processes, which monitor errors in protein folding, modification, and localization. However, little is known about how cells cope with translocation defective polypeptides that clog translocation channels (translocons) during protein translocation. This review summarizes recent studies, which collectively reveal a set of translocon-associated quality control strategies for eliminating polypeptides stuck in protein-conducting channels in the endoplasmic reticulum and mitochondria.
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Affiliation(s)
| | - Yihong Ye
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, United States
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46
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Lin KF, Fry MY, Saladi SM, Clemons WM. Molecular basis of tail-anchored integral membrane protein recognition by the cochaperone Sgt2. J Biol Chem 2021; 296:100441. [PMID: 33610544 PMCID: PMC8010706 DOI: 10.1016/j.jbc.2021.100441] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Revised: 02/04/2021] [Accepted: 02/17/2021] [Indexed: 02/08/2023] Open
Abstract
The targeting and insertion of tail-anchored (TA) integral membrane proteins (IMPs) into the correct membrane is critical for cellular homeostasis. The fungal protein Sgt2, and its human homolog SGTA, is the entry point for clients to the guided entry of tail-anchored protein (GET) pathway, which targets endoplasmic reticulum-bound TA IMPs. Consisting of three structurally independent domains, the C terminus of Sgt2 binds to the hydrophobic transmembrane domain (TMD) of clients. However, the exact binding interface within Sgt2 and molecular details that underlie its binding mechanism and client preference are not known. Here, we reveal the mechanism of Sgt2 binding to hydrophobic clients, including TA IMPs. Through sequence analysis, biophysical characterization, and a series of capture assays, we establish that the Sgt2 C-terminal domain is flexible but conserved and sufficient for client binding. A molecular model for this domain reveals a helical hand forming a hydrophobic groove approximately 15 Å long that is consistent with our observed higher affinity for client TMDs with a hydrophobic face and a minimal length of 11 residues. This work places Sgt2 into a broader family of TPR-containing cochaperone proteins, demonstrating structural and sequence-based similarities to the DP domains in the yeast Hsp90 and Hsp70 coordinating protein, Sti1.
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Affiliation(s)
- Ku-Feng Lin
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA
| | - Michelle Y Fry
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA
| | - Shyam M Saladi
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA
| | - William M Clemons
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA.
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47
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Galstyan V, Husain K, Xiao F, Murugan A, Phillips R. Proofreading through spatial gradients. eLife 2020; 9:60415. [PMID: 33357378 PMCID: PMC7813546 DOI: 10.7554/elife.60415] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2020] [Accepted: 12/24/2020] [Indexed: 12/01/2022] Open
Abstract
Key enzymatic processes use the nonequilibrium error correction mechanism called kinetic proofreading to enhance their specificity. The applicability of traditional proofreading schemes, however, is limited because they typically require dedicated structural features in the enzyme, such as a nucleotide hydrolysis site or multiple intermediate conformations. Here, we explore an alternative conceptual mechanism that achieves error correction by having substrate binding and subsequent product formation occur at distinct physical locations. The time taken by the enzyme–substrate complex to diffuse from one location to another is leveraged to discard wrong substrates. This mechanism does not have the typical structural requirements, making it easier to overlook in experiments. We discuss how the length scales of molecular gradients dictate proofreading performance, and quantify the limitations imposed by realistic diffusion and reaction rates. Our work broadens the applicability of kinetic proofreading and sets the stage for studying spatial gradients as a possible route to specificity.
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Affiliation(s)
- Vahe Galstyan
- Biochemistry and Molecular Biophysics Option, California Institute of Technology, Pasadena, United States
| | - Kabir Husain
- Department of Physics and the James Franck Institute, University of Chicago, Chicago, United States
| | - Fangzhou Xiao
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, United States
| | - Arvind Murugan
- Department of Physics and the James Franck Institute, University of Chicago, Chicago, United States
| | - Rob Phillips
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, United States.,Department of Physics, California Institute of Technology, Pasadena, United States
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48
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Endoplasmic reticulum membrane receptors of the GET pathway are conserved throughout eukaryotes. Proc Natl Acad Sci U S A 2020; 118:2017636118. [PMID: 33443185 PMCID: PMC7817167 DOI: 10.1073/pnas.2017636118] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The GET pathway is required for the insertion of tail-anchored (TA) membrane proteins in the endoplasmic reticulum (ER) of yeast and mammals. Some orthologous genes had also been identified in higher plants with the exception of one of the two ER membrane receptors required for membrane insertion. Get2/CAML is required for the pathway’s cytosolic chaperone to dock and release its TA protein cargo. Here we report the identification of the elusive plant GET pathway receptor through an interaction screen in Arabidopsis. The candidate allows detection of further Get2/CAML orthologs in higher plants, revealing conservation and function of structural features across kingdoms. Additionally, our results demonstrate that these features, rather than sequence conservation, determine functionality of the candidate within the pathway. Type II tail-anchored (TA) membrane proteins are involved in diverse cellular processes, including protein translocation, vesicle trafficking, and apoptosis. They are characterized by a single C-terminal transmembrane domain that mediates posttranslational targeting and insertion into the endoplasmic reticulum (ER) via the Guided-Entry of TA proteins (GET) pathway. The GET system was originally described in mammals and yeast but was recently shown to be partially conserved in other eukaryotes, such as higher plants. A newly synthesized TA protein is shielded from the cytosol by a pretargeting complex and an ATPase that delivers the protein to the ER, where membrane receptors (Get1/WRB and Get2/CAML) facilitate insertion. In the model plant Arabidopsis thaliana, most components of the pathway were identified through in silico sequence comparison, however, a functional homolog of the coreceptor Get2/CAML remained elusive. We performed immunoprecipitation-mass spectrometry analysis to detect in vivo interactors of AtGET1 and identified a membrane protein of unknown function with low sequence homology but high structural homology to both yeast Get2 and mammalian CAML. The protein localizes to the ER membrane, coexpresses with AtGET1, and binds to Arabidopsis GET pathway components. While loss-of-function lines phenocopy the stunted root hair phenotype of other Atget lines, its heterologous expression together with the coreceptor AtGET1 rescues growth defects of Δget1get2 yeast. Ectopic expression of the cytosolic, positively charged N terminus is sufficient to block TA protein insertion in vitro. Our results collectively confirm that we have identified a plant-specific GET2 in Arabidopsis, and its sequence allows the analysis of cross-kingdom pathway conservation.
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49
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Jiang H. Quality control pathways of tail-anchored proteins. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2020; 1868:118922. [PMID: 33285177 DOI: 10.1016/j.bbamcr.2020.118922] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Revised: 11/14/2020] [Accepted: 12/01/2020] [Indexed: 12/20/2022]
Abstract
Tail-anchored (TA) proteins have an N-terminal domain in the cytosol and a C-terminal transmembrane domain anchored to a variety of organelle membranes. TA proteins are recognized by targeting factors at the transmembrane domain and C-terminal sequence and are guided to distinct membranes. The promiscuity of targeting sequences and the dysfunction of targeting pathways cause mistargeting of TA proteins. TA proteins are under surveillance by quality control pathways. For resident TA proteins at mitochondrial and ER membranes, intrinsic instability or stimuli induced degrons of the cytosolic and transmembrane domains are sensed by quality control factors to initiate degradation of TA proteins. These pathways are summarized as TA protein degradation-Cytosol (TAD-C) and TAD-Membrane (TAD-M) pathways. For mistargeted and a subset of solitary TA proteins at mitochondrial and peroxisomal membranes, a unique pathway has been revealed in recent years. Msp1/ATAD1 is an AAA-ATPase dually-localized to mitochondrial and peroxisomal membranes. It directly recognizes mistargeted and solitary TA proteins and dislocates them out of membrane. Dislocated substrates are subsequently ubiquitinated by the ER-resident Doa10 ubiquitin E3 ligase complex for degradation. We summarize and discuss the substrate recognition, dislocation and degradation mechanisms of the Msp1 pathway.
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Affiliation(s)
- Hui Jiang
- National Institute of Biological Sciences, Beijing 102206, China; Beijing Key Laboratory of Cell Biology for Animal Aging, Beijing 102206, China; Tsinghua Institute of Multidisciplinary Biomedical Research, Tsinghua University, Beijing 100871, China.
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50
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Wang L, Walter P. Msp1/ATAD1 in Protein Quality Control and Regulation of Synaptic Activities. Annu Rev Cell Dev Biol 2020; 36:141-164. [DOI: 10.1146/annurev-cellbio-031220-015840] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Mitochondrial function depends on the efficient import of proteins synthesized in the cytosol. When cells experience stress, the efficiency and faithfulness of the mitochondrial protein import machinery are compromised, leading to homeostatic imbalances and damage to the organelle. Yeast Msp1 (mitochondrial sorting of proteins 1) and mammalian ATAD1 (ATPase family AAA domain–containing 1) are orthologous AAA proteins that, fueled by ATP hydrolysis, recognize and extract mislocalized membrane proteins from the outer mitochondrial membrane. Msp1 also extracts proteins that have become stuck in the import channel. The extracted proteins are targeted for proteasome-dependent degradation or, in the case of mistargeted tail-anchored proteins, are given another chance to be routed correctly. In addition, ATAD1 is implicated in the regulation of synaptic plasticity, mediating the release of neurotransmitter receptors from postsynaptic scaffolds to allow their trafficking. Here we discuss how structural and functional specialization imparts the unique properties that allow Msp1/ATAD1 ATPases to fulfill these diverse functions and also highlight outstanding questions in the field.
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Affiliation(s)
- Lan Wang
- Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California 94143, USA;,
| | - Peter Walter
- Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California 94143, USA;,
- Howard Hughes Medical Institute, University of California at San Francisco, San Francisco, California 94122, USA
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