1
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The Role of Protein Disorder in Nuclear Transport and in Its Subversion by Viruses. Cells 2020; 9:cells9122654. [PMID: 33321790 PMCID: PMC7764567 DOI: 10.3390/cells9122654] [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] [Received: 10/12/2020] [Revised: 12/08/2020] [Accepted: 12/08/2020] [Indexed: 12/12/2022] Open
Abstract
The transport of host proteins into and out of the nucleus is key to host function. However, nuclear transport is restricted by nuclear pores that perforate the nuclear envelope. Protein intrinsic disorder is an inherent feature of this selective transport barrier and is also a feature of the nuclear transport receptors that facilitate the active nuclear transport of cargo, and the nuclear transport signals on the cargo itself. Furthermore, intrinsic disorder is an inherent feature of viral proteins and viral strategies to disrupt host nucleocytoplasmic transport to benefit their replication. In this review, we highlight the role that intrinsic disorder plays in the nuclear transport of host and viral proteins. We also describe viral subversion mechanisms of the host nuclear transport machinery in which intrinsic disorder is a feature. Finally, we discuss nuclear import and export as therapeutic targets for viral infectious disease.
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2
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Martin APJ, Camonis JH. The hippo kinase STK38 ensures functionality of XPO1. Cell Cycle 2020; 19:2982-2995. [PMID: 33017560 PMCID: PMC7714482 DOI: 10.1080/15384101.2020.1826619] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2020] [Revised: 08/06/2020] [Accepted: 08/08/2020] [Indexed: 10/23/2022] Open
Abstract
The proper segregation of basic elements such as the compartmentalization of the genome and the shuttling of macromolecules between the nucleus and the cytoplasm is a crucial mechanism for homeostasis maintenance in eukaryotic cells. XPO1 (Exportin 1) is the major nuclear export receptor and is required for the export of proteins and RNAs out of the nucleus. STK38 (also known as NDR1) is a Hippo pathway serine/threonine kinase with multifarious functions in normal and cancer cells. In this review, we summarize the history of the discovery of the nucleo/cytoplasmic shuttling of proteins and focus on the major actor of nuclear export: XPO1. After describing the molecular events required for XPO1-mediated nuclear export of proteins, we introduce the Hippo pathway STK38 kinase, synthetize its regulation mechanisms as well as its biological functions in both normal and cancer cells, and finally its intersection with XPO1 biology. We discuss the recently identified mechanism of XPO1 activation by phosphorylation of XPO1_S1055 by STK38 and contextualize this finding according to the biological functions previously reported for both XPO1 and STK38, including the second identity of STK38 as an autophagy regulator. Finally, we phrase this newly identified activation mechanism into the general nuclear export machinery and examine the possible outcomes of nuclear export inhibition in cancer treatment.
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Affiliation(s)
- Alexandre PJ Martin
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, USA
| | - Jacques H Camonis
- Inserm U830, Institut Curie, Centre de Recherche, Paris Sciences et Lettres Research University, Paris, France
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3
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Sendino M, Omaetxebarria MJ, Prieto G, Rodriguez JA. Using a Simple Cellular Assay to Map NES Motifs in Cancer-Related Proteins, Gain Insight into CRM1-Mediated NES Export, and Search for NES-Harboring Micropeptides. Int J Mol Sci 2020; 21:E6341. [PMID: 32882917 PMCID: PMC7503480 DOI: 10.3390/ijms21176341] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2020] [Revised: 08/24/2020] [Accepted: 08/26/2020] [Indexed: 12/26/2022] Open
Abstract
The nuclear export receptor CRM1 (XPO1) recognizes and binds specific sequence motifs termed nuclear export signals (NESs) in cargo proteins. About 200 NES motifs have been identified, but over a thousand human proteins are potential CRM1 cargos, and most of their NESs remain to be identified. On the other hand, the interaction of NES peptides with the "NES-binding groove" of CRM1 was studied in detail using structural and biochemical analyses, but a better understanding of CRM1 function requires further investigation of how the results from these in vitro studies translate into actual NES export in a cellular context. Here we show that a simple cellular assay, based on a recently described reporter (SRVB/A), can be applied to identify novel potential NESs motifs, and to obtain relevant information on different aspects of CRM1-mediated NES export. Using cellular assays, we first map 19 new sequence motifs with nuclear export activity in 14 cancer-related proteins that are potential CRM1 cargos. Next, we investigate the effect of mutations in individual NES-binding groove residues, providing further insight into CRM1-mediated NES export. Finally, we extend the search for CRM1-dependent NESs to a recently uncovered, but potentially vast, set of small proteins called micropeptides. By doing so, we report the first NES-harboring human micropeptides.
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Affiliation(s)
- Maria Sendino
- Department of Genetics, Physical Anthropology and Animal Physiology, University of the Basque Country (UPV/EHU), 48940 Leioa, Spain;
| | - Miren Josu Omaetxebarria
- Department of Biochemistry and Molecular Biology, University of the Basque Country (UPV/EHU), 48940 Leioa, Spain;
| | - Gorka Prieto
- Department of Communications Engineering, University of the Basque Country (UPV/EHU), 48013 Bilbao, Spain;
| | - Jose Antonio Rodriguez
- Department of Genetics, Physical Anthropology and Animal Physiology, University of the Basque Country (UPV/EHU), 48940 Leioa, Spain;
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4
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Shaikhqasem A, Dickmanns A, Neumann P, Ficner R. Characterization of Inhibition Reveals Distinctive Properties for Human and Saccharomyces cerevisiae CRM1. J Med Chem 2020; 63:7545-7558. [PMID: 32585100 DOI: 10.1021/acs.jmedchem.0c00143] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The receptor CRM1 is responsible for the nuclear export of many tumor-suppressor proteins and viral ribonucleoproteins. This renders CRM1 an interesting target for therapeutic intervention in diverse cancer types and viral diseases. Structural studies of Saccharomyces cerevisiae CRM1 (ScCRM1) complexes with inhibitors defined the molecular basis for CRM1 inhibition. Nevertheless, no structural information is available for inhibitors bound to human CRM1 (HsCRM1). Here, we present the structure of the natural inhibitor Leptomycin B bound to the HsCRM1-RanGTP complex. Despite high sequence conservation and structural similarity in the NES-binding cleft region, ScCRM1 exhibits 16-fold lower binding affinity than HsCRM1 toward PKI-NES and significant differences in affinities toward potential CRM1 inhibitors. In contrast to HsCRM1, competition assays revealed that a human adapted mutant ScCRM1-T539C does not bind all inhibitors tested. Taken together, our data indicate the importance of using HsCRM1 for molecular analysis and development of novel antitumor and antiviral drugs.
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Affiliation(s)
- Alaa Shaikhqasem
- Department of Molecular Structural Biology, Institute of Microbiology and Genetics, GZMB, Georg-August-University Göttingen, 37077 Göttingen, Germany
| | - Achim Dickmanns
- Department of Molecular Structural Biology, Institute of Microbiology and Genetics, GZMB, Georg-August-University Göttingen, 37077 Göttingen, Germany
| | - Piotr Neumann
- Department of Molecular Structural Biology, Institute of Microbiology and Genetics, GZMB, Georg-August-University Göttingen, 37077 Göttingen, Germany
| | - Ralf Ficner
- Department of Molecular Structural Biology, Institute of Microbiology and Genetics, GZMB, Georg-August-University Göttingen, 37077 Göttingen, Germany
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5
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Liao CC, Shankar S, Pi WC, Chang CC, Ahmed GR, Chen WY, Hsia KC. Karyopherin Kap114p-mediated trans-repression controls ribosomal gene expression under saline stress. EMBO Rep 2020; 21:e48324. [PMID: 32484313 DOI: 10.15252/embr.201948324] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2019] [Revised: 04/16/2020] [Accepted: 04/30/2020] [Indexed: 01/01/2023] Open
Abstract
Nuclear accessibility of transcription factors controls gene expression, co-regulated by Ran-dependent nuclear localization and a competitive regulatory network. Here, we reveal that nuclear import factor-facilitated transcriptional repression attenuates ribosome biogenesis under chronic salt stress. Kap114p, one of the karyopherin-βs (Kap-βs) that mediates nuclear import of yeast TATA-binding protein (yTBP), exhibits a yTBP-binding affinity four orders of magnitude greater than its counterparts and suppresses binding of yTBP with DNA. Our crystal structure of Kap114p reveals an extensively negatively charged concave surface, accounting for high-affinity basic-protein binding. KAP114 knockout in yeast leads to a high-salt growth defect, with transcriptomic analyses revealing that Kap114p modulates expression of genes associated with ribosomal biogenesis by suppressing yTBP binding to target promoters, a trans-repression mechanism we attribute to reduced nuclear Ran levels under salinity stress. Our findings reveal that Ran integrates the nuclear transport pathway and transcription regulatory network, allowing yeast to respond to environmental stresses.
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Affiliation(s)
- Chung-Chi Liao
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
| | - Sahana Shankar
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
| | - Wen-Chieh Pi
- Institute of Biochemistry and Molecular Biology, College of Life Sciences, National Yang-Ming University, Taipei, Taiwan
| | - Chih-Chia Chang
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
| | | | - Wei-Yi Chen
- Institute of Biochemistry and Molecular Biology, College of Life Sciences, National Yang-Ming University, Taipei, Taiwan
| | - Kuo-Chiang Hsia
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan.,Institute of Biochemistry and Molecular Biology, College of Life Sciences, National Yang-Ming University, Taipei, Taiwan
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6
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Lei Y, An Q, Zhang Y, Luo P, Luo Y, Shen X, Jia D, Sun Q. Engineering chromosome region maintenance 1 fragments that bind to nuclear export signals. Protein Sci 2020; 29:1366-1372. [PMID: 31495993 PMCID: PMC7255508 DOI: 10.1002/pro.3724] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2019] [Revised: 09/02/2019] [Accepted: 09/03/2019] [Indexed: 02/05/2023]
Abstract
Chromosome region maintenance 1 (CRM1) exports nuclear export signal (NES) containing cargos from nucleus to cytoplasm and plays critical roles in cancer and viral infections. Biochemical and biophysical studies on this protein were often obstructed by its low purification yield and stability. With the help of PROSS server and NES protection strategy, we successfully designed three small fragments of CRM1, each made of four HEAT repeats and capable of binding to NESs in the absence of RanGTP. One of the fragments, C7, showed dramatically improved purification yield, thermostability, mechanostability, and resistance to protease digestion. We showed by isothermal titration that the protein kinase inhibitor NES binds to C7 at 1.18 μM affinity. Direct binding to C7 by several reported CRM1 inhibitors derived from plants were verified using pull-down assays. These fragments might be useful for the development of CRM1 inhibitors towards treatment of related diseases. The strategy applied here might help to tackle similar problems encountered in different fields.
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Affiliation(s)
- Yuqin Lei
- Department of Pathology, State Key Laboratory of Biotherapy and Cancer Center, West China HospitalSichuan University, and Collaborative Innovation Centre of BiotherapyChengduChina
| | - Qi An
- Department of Pathology, State Key Laboratory of Biotherapy and Cancer Center, West China HospitalSichuan University, and Collaborative Innovation Centre of BiotherapyChengduChina
| | - Yuqing Zhang
- Department of Pathology, State Key Laboratory of Biotherapy and Cancer Center, West China HospitalSichuan University, and Collaborative Innovation Centre of BiotherapyChengduChina
| | - Ping Luo
- Department of Pathology, State Key Laboratory of Biotherapy and Cancer Center, West China HospitalSichuan University, and Collaborative Innovation Centre of BiotherapyChengduChina
| | - Youfu Luo
- Department of Pathology, State Key Laboratory of Biotherapy and Cancer Center, West China HospitalSichuan University, and Collaborative Innovation Centre of BiotherapyChengduChina
| | - Xiaofei Shen
- Key Laboratory of Birth Defects and Related Diseases of Women and Children, Department of Paediatrics, Division of NeurologyWest China Second University Hospital, Sichuan UniversityChengduChina
| | - Da Jia
- Key Laboratory of Birth Defects and Related Diseases of Women and Children, Department of Paediatrics, Division of NeurologyWest China Second University Hospital, Sichuan UniversityChengduChina
| | - Qingxiang Sun
- Department of Pathology, State Key Laboratory of Biotherapy and Cancer Center, West China HospitalSichuan University, and Collaborative Innovation Centre of BiotherapyChengduChina
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7
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Oka M, Mura S, Otani M, Miyamoto Y, Nogami J, Maehara K, Harada A, Tachibana T, Yoneda Y, Ohkawa Y. Chromatin-bound CRM1 recruits SET-Nup214 and NPM1c onto HOX clusters causing aberrant HOX expression in leukemia cells. eLife 2019; 8:e46667. [PMID: 31755865 PMCID: PMC6874418 DOI: 10.7554/elife.46667] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Accepted: 10/30/2019] [Indexed: 12/14/2022] Open
Abstract
We previously demonstrated that CRM1, a major nuclear export factor, accumulates at Hox cluster regions to recruit nucleoporin-fusion protein Nup98HoxA9, resulting in robust activation of Hox genes (Oka et al., 2016). However, whether this phenomenon is general to other leukemogenic proteins remains unknown. Here, we show that two other leukemogenic proteins, nucleoporin-fusion SET-Nup214 and the NPM1 mutant, NPM1c, which contains a nuclear export signal (NES) at its C-terminus and is one of the most frequent mutations in acute myeloid leukemia, are recruited to the HOX cluster region via chromatin-bound CRM1, leading to HOX gene activation in human leukemia cells. Furthermore, we demonstrate that this mechanism is highly sensitive to a CRM1 inhibitor in leukemia cell line. Together, these findings indicate that CRM1 acts as a key molecule that connects leukemogenic proteins to aberrant HOX gene regulation either via nucleoporin-CRM1 interaction (for SET-Nup214) or NES-CRM1 interaction (for NPM1c).
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Affiliation(s)
- Masahiro Oka
- Laboratory of Nuclear Transport DynamicsNational Institutes of Biomedical Innovation, Health and Nutrition (NIBIOHN)OsakaJapan
- Laboratory of Biomedical Innovation, Graduate School of Pharmaceutical SciencesOsaka UniversityOsakaJapan
| | - Sonoko Mura
- Biomolecular Dynamics Group, Graduate School of Frontier BiosciencesOsaka UniversityOsakaJapan
| | - Mayumi Otani
- Laboratory of Nuclear Transport DynamicsNational Institutes of Biomedical Innovation, Health and Nutrition (NIBIOHN)OsakaJapan
| | - Yoichi Miyamoto
- Laboratory of Nuclear Transport DynamicsNational Institutes of Biomedical Innovation, Health and Nutrition (NIBIOHN)OsakaJapan
| | - Jumpei Nogami
- Department of Advanced Medical Initiatives, Faculty of MedicineKyushu UniversityFukuokaJapan
| | - Kazumitsu Maehara
- Department of Advanced Medical Initiatives, Faculty of MedicineKyushu UniversityFukuokaJapan
| | - Akihito Harada
- Department of Advanced Medical Initiatives, Faculty of MedicineKyushu UniversityFukuokaJapan
| | - Taro Tachibana
- Department of Bioengineering, Graduate School of EngineeringOsaka City UniversityOsakaJapan
| | - Yoshihiro Yoneda
- Laboratory of Biomedical Innovation, Graduate School of Pharmaceutical SciencesOsaka UniversityOsakaJapan
- National Institutes of Biomedical Innovation, Health and Nutrition (NIBIOHN)OsakaJapan
| | - Yasuyuki Ohkawa
- Department of Advanced Medical Initiatives, Faculty of MedicineKyushu UniversityFukuokaJapan
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8
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Camus V, Miloudi H, Taly A, Sola B, Jardin F. XPO1 in B cell hematological malignancies: from recurrent somatic mutations to targeted therapy. J Hematol Oncol 2017; 10:47. [PMID: 28196522 PMCID: PMC5307790 DOI: 10.1186/s13045-017-0412-4] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2016] [Accepted: 01/31/2017] [Indexed: 02/07/2023] Open
Abstract
Many recent publications highlight the large role of the pivotal eukaryotic nuclear export protein exportin-1 (XPO1) in the oncogenesis of several malignancies, and there is emerging evidence that XPO1 inhibition is a key target against cancer. The clinical validation of the pharmacological inhibition of XPO1 was recently achieved with the development of the selective inhibitor of nuclear export compounds, displaying an interesting anti-tumor activity in patients with massive pre-treated hematological malignancies. Recent reports have shown molecular alterations in the gene encoding XPO1 and showed a mutation hotspot (E571K) in the following two hematological malignancies with similar phenotypes and natural histories: primary mediastinal diffuse large B cell lymphoma and classical Hodgkin's lymphoma. Emerging evidence suggests that the mutant XPO1 E571K plays a role in carcinogenesis, and this variant is quantifiable in tumor and plasma cell-free DNA of patients using highly sensitive molecular biology techniques, such as digital PCR and next-generation sequencing. Therefore, it was proposed that the XPO1 E571K variant may serve as a minimal residual disease tool in this setting. To clarify and summarize the recent findings on the role of XPO1 in B cell hematological malignancies, we conducted a literature search to present the major publications establishing the landscape of XPO1 molecular alterations, their impact on the XPO1 protein, their interest as biomarkers, and investigations into the development of new XPO1-targeted therapies in B cell hematological malignancies.
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Affiliation(s)
- Vincent Camus
- Normandie Univ, INSERM U1245, UNICAEN, UNIROUEN, Caen, France
- Department of Hematology, Centre Henri Becquerel, Rouen, France
| | - Hadjer Miloudi
- Normandie Univ, INSERM U1245, UNICAEN, UNIROUEN, Caen, France
| | - Antoine Taly
- Laboratoire de Biochimie Théorique, Institut de Biologie Physico-Chimique, CNRS, Université Paris Diderot, Paris, France
| | - Brigitte Sola
- Normandie Univ, INSERM U1245, UNICAEN, UNIROUEN, Caen, France.
| | - Fabrice Jardin
- Normandie Univ, INSERM U1245, UNICAEN, UNIROUEN, Caen, France
- Department of Hematology, Centre Henri Becquerel, Rouen, France
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9
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García-Santisteban I, Arregi I, Alonso-Mariño M, Urbaneja MA, Garcia-Vallejo JJ, Bañuelos S, Rodríguez JA. A cellular reporter to evaluate CRM1 nuclear export activity: functional analysis of the cancer-related mutant E571K. Cell Mol Life Sci 2016; 73:4685-4699. [PMID: 27312238 PMCID: PMC11108298 DOI: 10.1007/s00018-016-2292-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2016] [Revised: 05/10/2016] [Accepted: 06/07/2016] [Indexed: 01/02/2023]
Abstract
The exportin CRM1 binds nuclear export signals (NESs), and mediates active transport of NES-bearing proteins from the nucleus to the cytoplasm. Structural and biochemical analyses have uncovered the molecular mechanisms underlying CRM1/NES interaction. CRM1 binds NESs through a hydrophobic cleft, whose open or closed conformation facilitates NES binding and release. Several cofactors allosterically modulate the conformation of the NES-binding cleft through intramolecular interactions involving an acidic loop and a C-terminal helix in CRM1. This current model of CRM1-mediated nuclear export has not yet been evaluated in a cellular setting. Here, we describe SRV100, a cellular reporter to interrogate CRM1 nuclear export activity. Using this novel tool, we provide evidence further validating the model of NES binding and release by CRM1. Furthermore, using both SRV100-based cellular assays and in vitro biochemical analyses, we investigate the functional consequences of a recurrent cancer-related mutation, which targets a residue near CRM1 NES-binding cleft. Our data indicate that this mutation does not necessarily abrogate the nuclear export activity of CRM1, but may increase its affinity for NES sequences bearing a more negatively charged C-terminal end.
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Affiliation(s)
- Iraia García-Santisteban
- Department of Genetics, Physical Anthropology and Animal Physiology, University of the Basque Country (UPV/EHU), Leioa, Spain
- Division of Cell Biology I, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Igor Arregi
- Department of Biochemistry and Molecular Biology, Biofisika Institute (UPV/EHU, CSIC), University of the Basque Country, Leioa, Spain
| | - Marián Alonso-Mariño
- Department of Biochemistry and Molecular Biology, Biofisika Institute (UPV/EHU, CSIC), University of the Basque Country, Leioa, Spain
| | - María A Urbaneja
- Department of Biochemistry and Molecular Biology, Biofisika Institute (UPV/EHU, CSIC), University of the Basque Country, Leioa, Spain
| | - Juan J Garcia-Vallejo
- Department of Molecular Cell Biology and Immunology, VU University Medical Center, Amsterdam, The Netherlands
| | - Sonia Bañuelos
- Department of Biochemistry and Molecular Biology, Biofisika Institute (UPV/EHU, CSIC), University of the Basque Country, Leioa, Spain.
| | - Jose A Rodríguez
- Department of Genetics, Physical Anthropology and Animal Physiology, University of the Basque Country (UPV/EHU), Leioa, Spain.
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10
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Matsuura Y. Mechanistic Insights from Structural Analyses of Ran-GTPase-Driven Nuclear Export of Proteins and RNAs. J Mol Biol 2015; 428:2025-39. [PMID: 26519791 DOI: 10.1016/j.jmb.2015.09.025] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2015] [Accepted: 09/28/2015] [Indexed: 12/13/2022]
Abstract
Understanding how macromolecules are rapidly exchanged between the nucleus and the cytoplasm through nuclear pore complexes is a fundamental problem in biology. Exportins are Ran-GTPase-dependent nuclear transport factors that belong to the karyopherin-β family and mediate nuclear export of a plethora of proteins and RNAs, except for bulk mRNA nuclear export. Exportins bind cargo macromolecules in a Ran-GTP-dependent manner in the nucleus, forming exportin-cargo-Ran-GTP complexes (nuclear export complexes). Transient weak interactions between exportins and nucleoporins containing characteristic FG (phenylalanine-glycine) repeat motifs facilitate nuclear pore complex passage of nuclear export complexes. In the cytoplasm, nuclear export complexes are disassembled, thereby releasing the cargo. GTP hydrolysis by Ran promoted in the cytoplasm makes the disassembly reaction virtually irreversible and provides thermodynamic driving force for the overall export reaction. In the past decade, X-ray crystallography of some of the exportins in various functional states coupled with functional analyses, single-particle electron microscopy, molecular dynamics simulations, and small-angle solution X-ray scattering has provided rich insights into the mechanism of cargo binding and release and also begins to elucidate how exportins interact with the FG repeat motifs. The knowledge gained from structural analyses of nuclear export is being translated into development of clinically useful inhibitors of nuclear export to treat human diseases such as cancer and influenza.
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Affiliation(s)
- Yoshiyuki Matsuura
- Division of Biological Science and Structural Biology Research Center, Graduate School of Science, Nagoya University, Nagoya 466-8550, Japan.
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11
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Dickmanns A, Monecke T, Ficner R. Structural Basis of Targeting the Exportin CRM1 in Cancer. Cells 2015; 4:538-68. [PMID: 26402707 PMCID: PMC4588050 DOI: 10.3390/cells4030538] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Revised: 09/07/2015] [Accepted: 09/11/2015] [Indexed: 12/19/2022] Open
Abstract
Recent studies have demonstrated the interference of nucleocytoplasmic trafficking with the establishment and maintenance of various cancers. Nucleocytoplasmic transport is highly regulated and coordinated, involving different nuclear transport factors or receptors, importins and exportins, that mediate cargo transport from the cytoplasm into the nucleus or the other way round, respectively. The exportin CRM1 (Chromosome region maintenance 1) exports a plethora of different protein cargoes and ribonucleoprotein complexes. Structural and biochemical analyses have enabled the deduction of individual steps of the CRM1 transport cycle. In addition, CRM1 turned out to be a valid target for anticancer drugs as it exports numerous proto-oncoproteins and tumor suppressors. Clearly, detailed understanding of the flexibility, regulatory features and cooperative binding properties of CRM1 for Ran and cargo is a prerequisite for the design of highly effective drugs. The first compound found to inhibit CRM1-dependent nuclear export was the natural drug Leptomycin B (LMB), which blocks export by competitively interacting with a highly conserved cleft on CRM1 required for nuclear export signal recognition. Clinical studies revealed serious side effects of LMB, leading to a search for alternative natural and synthetic drugs and hence a multitude of novel therapeutics. The present review examines recent progress in understanding the binding mode of natural and synthetic compounds and their inhibitory effects.
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Affiliation(s)
- Achim Dickmanns
- Abteilung für Molekulare Strukturbiologie, Institut für Mikrobiologie und Genetik, GZMB, Georg-August-Universität Göttingen, Justus-von-Liebig-Weg 11, Göttingen 37077, Germany.
| | - Thomas Monecke
- Abteilung für Molekulare Strukturbiologie, Institut für Mikrobiologie und Genetik, GZMB, Georg-August-Universität Göttingen, Justus-von-Liebig-Weg 11, Göttingen 37077, Germany.
| | - Ralf Ficner
- Abteilung für Molekulare Strukturbiologie, Institut für Mikrobiologie und Genetik, GZMB, Georg-August-Universität Göttingen, Justus-von-Liebig-Weg 11, Göttingen 37077, Germany.
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12
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Arregi I, Falces J, Olazabal-Herrero A, Alonso-Mariño M, Taneva SG, Rodríguez JA, Urbaneja MA, Bañuelos S. Leukemia-Associated Mutations in Nucleophosmin Alter Recognition by CRM1: Molecular Basis of Aberrant Transport. PLoS One 2015; 10:e0130610. [PMID: 26091065 PMCID: PMC4474691 DOI: 10.1371/journal.pone.0130610] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2014] [Accepted: 05/21/2015] [Indexed: 12/31/2022] Open
Abstract
Nucleophosmin (NPM) is a nucleocytoplasmic shuttling protein, normally enriched in nucleoli, that performs several activities related to cell growth. NPM mutations are characteristic of a subtype of acute myeloid leukemia (AML), where mutant NPM seems to play an oncogenic role. AML-associated NPM mutants exhibit altered subcellular traffic, being aberrantly located in the cytoplasm of leukoblasts. Exacerbated export of AML variants of NPM is mediated by the nuclear export receptor CRM1, and due, in part, to a mutationally acquired novel nuclear export signal (NES). To gain insight on the molecular basis of NPM transport in physiological and pathological conditions, we have evaluated the export efficiency of NPM in cells, and present new data indicating that, in normal conditions, wild type NPM is weakly exported by CRM1. On the other hand, we have found that AML-associated NPM mutants efficiently form complexes with CRM1HA (a mutant CRM1 with higher affinity for NESs), and we have quantitatively analyzed CRM1HA interaction with the NES motifs of these mutants, using fluorescence anisotropy and isothermal titration calorimetry. We have observed that the affinity of CRM1HA for these NESs is similar, which may help to explain the transport properties of the mutants. We also describe NPM recognition by the import machinery. Our combined cellular and biophysical studies shed further light on the determinants of NPM traffic, and how it is dramatically altered by AML-related mutations.
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Affiliation(s)
- Igor Arregi
- Unidad de Biofísica (CSIC, UPV/EHU) and Department of Biochemistry and Molecular Biology, University of the Basque Country, Leioa, Spain
| | - Jorge Falces
- Unidad de Biofísica (CSIC, UPV/EHU) and Department of Biochemistry and Molecular Biology, University of the Basque Country, Leioa, Spain
| | - Anne Olazabal-Herrero
- Department of Genetics, Physical Anthropology and Animal Physiology, University of the Basque Country, Leioa, Spain
| | - Marián Alonso-Mariño
- Unidad de Biofísica (CSIC, UPV/EHU) and Department of Biochemistry and Molecular Biology, University of the Basque Country, Leioa, Spain
| | - Stefka G. Taneva
- Unidad de Biofísica (CSIC, UPV/EHU) and Department of Biochemistry and Molecular Biology, University of the Basque Country, Leioa, Spain
| | - José A. Rodríguez
- Department of Genetics, Physical Anthropology and Animal Physiology, University of the Basque Country, Leioa, Spain
| | - María A. Urbaneja
- Unidad de Biofísica (CSIC, UPV/EHU) and Department of Biochemistry and Molecular Biology, University of the Basque Country, Leioa, Spain
| | - Sonia Bañuelos
- Unidad de Biofísica (CSIC, UPV/EHU) and Department of Biochemistry and Molecular Biology, University of the Basque Country, Leioa, Spain
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13
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Monecke T, Dickmanns A, Ficner R. Allosteric control of the exportin CRM1 unraveled by crystal structure analysis. FEBS J 2014; 281:4179-94. [PMID: 24823279 PMCID: PMC4231977 DOI: 10.1111/febs.12842] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Revised: 05/02/2014] [Accepted: 05/12/2014] [Indexed: 01/07/2023]
Abstract
Nucleocytoplasmic trafficking in eukaryotic cells is a highly regulated and coordinated process which involves an increasing variety of soluble nuclear transport receptors. Generally, transport receptors specifically bind their cargo and facilitate its transition through nuclear pore complexes, aqueous channels connecting the two compartments. Directionality of such transport events by receptors of the importin β superfamily requires the interaction with the small GTPase Ras-related nuclear antigen (Ran). While importins need RanGTP to release their cargo in the nucleus and thus to terminate import, exportins recruit cargo in the RanGTP-bound state. The exportin chromosome region maintenance 1 (CRM1) is a highly versatile transport receptor that exports a plethora of different protein and RNP cargoes. Moreover, binding of RanGTP and of cargo to CRM1 are highly cooperative events despite the fact that cargo and RanGTP do not interact directly in crystal structures of assembled export complexes. Integrative approaches have recently unraveled the individual steps of the CRM1 transport cycle at a structural level and explained how the HEAT-repeat architecture of CRM1 provides a framework for the key elements to mediate allosteric interactions with RanGTP, Ran binding proteins and cargo. Moreover, during the last decade, CRM1 has become a more and more appreciated target for anti-cancer drugs. Hence, detailed understanding of the flexibility, the regulatory features and the positive binding cooperativity between CRM1, Ran and cargo is a prerequisite for the development of highly effective drugs. Here we review recent structural advances in the characterization of CRM1 and CRM1-containing complexes with a special emphasis on X-ray crystallographic studies.
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Affiliation(s)
- Thomas Monecke
- Abteilung für Molekulare Strukturbiologie, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften, Georg-August-Universität Göttingen, Germany
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14
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Fung HYJ, Chook YM. Atomic basis of CRM1-cargo recognition, release and inhibition. Semin Cancer Biol 2014; 27:52-61. [PMID: 24631835 PMCID: PMC4108548 DOI: 10.1016/j.semcancer.2014.03.002] [Citation(s) in RCA: 106] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2014] [Accepted: 03/01/2014] [Indexed: 11/19/2022]
Abstract
CRM1 or XPO1 is the major nuclear export receptor in the cell, which controls the nuclear-cytoplasmic localization of many proteins and RNAs. CRM1 is also a promising cancer drug target as the transport receptor is overexpressed in many cancers where some of its cargos are misregulated and mislocalized to the cytoplasm. Atomic level understanding of CRM1 function has greatly facilitated recent drug discovery and development of CRM1 inhibitors to target a variety of malignancies. Numerous atomic resolution CRM1 structures are now available, explaining how the exporter recognizes nuclear export signals in its cargos, how RanGTP and cargo bind with positive cooperativity, how RanBP1 causes release of export cargos in the cytoplasm and how diverse inhibitors such as Leptomycin B and the new KPT-SINE compounds block nuclear export. This review summarizes structure-function studies that explain CRM1-cargo recognition, release and inhibition.
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Affiliation(s)
- Ho Yee Joyce Fung
- Department of Pharmacology, University of Texas Southwestern Medical Center at Dallas, 6001 Forest Park, Dallas, TX 75390-9041, USA.
| | - Yuh Min Chook
- Department of Pharmacology, University of Texas Southwestern Medical Center at Dallas, 6001 Forest Park, Dallas, TX 75390-9041, USA.
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15
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Kim S, Elbaum M. Enzymatically driven transport: a kinetic theory for nuclear export. Biophys J 2014; 105:1997-2005. [PMID: 24209844 DOI: 10.1016/j.bpj.2013.09.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2013] [Revised: 09/11/2013] [Accepted: 09/13/2013] [Indexed: 11/29/2022] Open
Abstract
Nuclear import and export are often considered inverse processes whereby transport receptors ferry protein cargo through the nuclear pore. In contrast to import, where the reversible binding of receptor to nuclear RanGTP leads to a balanced bidirectional exchange, termination of export by physiologically irreversible hydrolysis of the Ran-bound GTP leads to unidirectional transport. We present a concise mathematical model that predicts protein distributions and kinetic rates for receptor-mediated nuclear export, which further exhibit an unexpected pseudolinear relation one to the other. Predictions of the model are verified with permeabilized and live cell measurements.
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Affiliation(s)
- Sanghyun Kim
- Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel
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16
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Dölker N, Blanchet CE, Voß B, Haselbach D, Kappel C, Monecke T, Svergun DI, Stark H, Ficner R, Zachariae U, Grubmüller H, Dickmanns A. Structural determinants and mechanism of mammalian CRM1 allostery. Structure 2013; 21:1350-60. [PMID: 23850451 DOI: 10.1016/j.str.2013.05.015] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2013] [Revised: 05/07/2013] [Accepted: 05/26/2013] [Indexed: 10/26/2022]
Abstract
Proteins carrying nuclear export signals cooperatively assemble with the export factor CRM1 and the effector protein RanGTP. In lower eukaryotes, this cooperativity is coupled to CRM1 conformational changes; however, it is unknown if mammalian CRM1 maintains its compact conformation or shows similar structural flexibility. Here, combinations of small-angle X-ray solution scattering and electron microscopy experiments with molecular dynamics simulations reveal pronounced conformational flexibility in mammalian CRM1 and demonstrate that RanGTP binding induces association of its N- and C-terminal regions to form a toroid structure. The CRM1 toroid is stabilized mainly by local interactions between the terminal regions, rather than by global strain. The CRM1 acidic loop is key in transmitting the effect of this RanGTP-induced global conformational change to the NES-binding cleft by shifting its population to the open state, which displays enhanced cargo affinity. Cooperative CRM1 export complex assembly thus constitutes a highly dynamic process, encompassing an intricate interplay of global and local structural changes.
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Affiliation(s)
- Nicole Dölker
- Abteilung für Theoretische und Computergestützte Biophysik, Max-Planck-Institut für Biophysikalische Chemie, Am Faßberg 11, 37077 Göttingen, Germany
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17
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Dian C, Bernaudat F, Langer K, Oliva MF, Fornerod M, Schoehn G, Müller CW, Petosa C. Structure of a truncation mutant of the nuclear export factor CRM1 provides insights into the auto-inhibitory role of its C-terminal helix. Structure 2013; 21:1338-49. [PMID: 23850454 DOI: 10.1016/j.str.2013.06.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2013] [Revised: 06/12/2013] [Accepted: 06/13/2013] [Indexed: 11/23/2022]
Abstract
Chromosome region maintenance 1/exportin1/Xpo1 (CRM1) associates with the GTPase Ran to mediate the nuclear export of proteins bearing a leucine-rich nuclear export signal (NES). CRM1 consists of helical hairpin HEAT repeats and a C-terminal helical extension (C-extension) that inhibits the binding of NES-bearing cargos. We report the crystal structure and small-angle X-ray scattering analysis of a human CRM1 mutant with enhanced NES-binding activity due to deletion of the C-extension. We show that loss of the C-extension leads to a repositioning of CRM1's C-terminal repeats and to a more extended overall conformation. Normal mode analysis predicts reduced rigidity for the deletion mutant, consistent with an observed decrease in thermal stability. Point mutations that destabilize the C-extension shift CRM1 to the more extended conformation, reduce thermal stability, and enhance NES-binding activity. These findings suggest that an important mechanism by which the C-extension regulates CRM1's cargo-binding affinity is by modulating the conformation and flexibility of its HEAT repeats.
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Affiliation(s)
- Cyril Dian
- Université de Grenoble Alpes, Institut de Biologie Structurale, 38027 Grenoble, France
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18
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Kang SS, Shin SH. Phosphorylation of human chromosome maintenance 1 mediates association with 14-3-3 proteins. Anim Cells Syst (Seoul) 2013. [DOI: 10.1080/19768354.2013.801366] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
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19
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Saito N, Matsuura Y. A 2.1-Å-resolution crystal structure of unliganded CRM1 reveals the mechanism of autoinhibition. J Mol Biol 2013; 425:350-64. [PMID: 23164569 DOI: 10.1016/j.jmb.2012.11.014] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2012] [Revised: 11/02/2012] [Accepted: 11/07/2012] [Indexed: 11/27/2022]
Abstract
CRM1 mediates nuclear export of numerous proteins and ribonucleoproteins containing a leucine-rich nuclear export signal (NES). Binding of RanGTP to CRM1 in the nucleus stabilizes cargo association with CRM1, and vice versa, but the mechanism underlying the positive cooperativity in RanGTP and NES binding to CRM1 remains incompletely understood. Herein we report a 2.1-Å-resolution crystal structure of unliganded Saccharomyces cerevisiae CRM1 (Xpo1p) that demonstrates that an internal loop of CRM1 (referred to as HEAT9 loop) is primarily responsible for maintaining the NES-binding cleft in a closed conformation, rendering CRM1 incapable of NES binding in the absence of RanGTP. The structure also shows that the C-terminal tail of CRM1 stabilizes the autoinhibitory conformation of the HEAT9 loop and thereby reinforces autoinhibition. Comparison with the structures of CRM1-NES-RanGTP complexes reveals how binding of RanGTP is associated with a series of allosteric conformational changes in CRM1 that lead to opening of the NES-binding cleft, allowing for stable binding of NES cargoes.
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Affiliation(s)
- Natsumi Saito
- Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
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20
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Monecke T, Haselbach D, Voß B, Russek A, Neumann P, Thomson E, Hurt E, Zachariae U, Stark H, Grubmüller H, Dickmanns A, Ficner R. Structural basis for cooperativity of CRM1 export complex formation. Proc Natl Acad Sci U S A 2013; 110:960-5. [PMID: 23277578 PMCID: PMC3549083 DOI: 10.1073/pnas.1215214110] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In eukaryotes, the nucleocytoplasmic transport of macromolecules is mainly mediated by soluble nuclear transport receptors of the karyopherin-β superfamily termed importins and exportins. The highly versatile exportin chromosome region maintenance 1 (CRM1) is essential for nuclear depletion of numerous structurally and functionally unrelated protein and ribonucleoprotein cargoes. CRM1 has been shown to adopt a toroidal structure in several functional transport complexes and was thought to maintain this conformation throughout the entire nucleocytoplasmic transport cycle. We solved crystal structures of free CRM1 from the thermophilic eukaryote Chaetomium thermophilum. Surprisingly, unbound CRM1 exhibits an overall extended and pitched superhelical conformation. The two regulatory regions, namely the acidic loop and the C-terminal α-helix, are dramatically repositioned in free CRM1 in comparison with the ternary CRM1-Ran-Snurportin1 export complex. Single-particle EM analysis demonstrates that, in a noncrystalline environment, free CRM1 exists in equilibrium between extended, superhelical and compact, ring-like conformations. Molecular dynamics simulations show that the C-terminal helix plays an important role in regulating the transition from an extended to a compact conformation and reveal how the binding site for nuclear export signals of cargoes is modulated by different CRM1 conformations. Combining these results, we propose a model for the cooperativity of CRM1 export complex assembly involving the long-range allosteric communication between the distant binding sites of GTP-bound Ran and cargo.
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MESH Headings
- Active Transport, Cell Nucleus
- Allosteric Regulation
- Amino Acid Sequence
- Binding Sites
- Chaetomium/chemistry
- Chaetomium/genetics
- Chaetomium/metabolism
- Crystallography, X-Ray
- Fungal Proteins/chemistry
- Fungal Proteins/genetics
- Fungal Proteins/metabolism
- Fungal Proteins/ultrastructure
- Karyopherins/chemistry
- Karyopherins/genetics
- Karyopherins/metabolism
- Karyopherins/ultrastructure
- Microscopy, Electron
- Models, Biological
- Models, Molecular
- Molecular Dynamics Simulation
- Molecular Sequence Data
- Multiprotein Complexes/chemistry
- Multiprotein Complexes/metabolism
- Protein Conformation
- Receptors, Cytoplasmic and Nuclear/chemistry
- Receptors, Cytoplasmic and Nuclear/genetics
- Receptors, Cytoplasmic and Nuclear/metabolism
- Receptors, Cytoplasmic and Nuclear/ultrastructure
- Recombinant Fusion Proteins/chemistry
- Recombinant Fusion Proteins/genetics
- Recombinant Fusion Proteins/metabolism
- Recombinant Fusion Proteins/ultrastructure
- Sequence Homology, Amino Acid
- Static Electricity
- Exportin 1 Protein
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Affiliation(s)
- Thomas Monecke
- Abteilung für Molekulare Strukturbiologie, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften, Georg-August-Universität Göttingen, D-37077 Göttingen, Germany
| | - David Haselbach
- Dreidimensionale Kryo-Elektronenmikroskopie, Max-Planck-Institut für Biophysikalische Chemie, D-37077 Göttingen, Germany
| | - Béla Voß
- Abteilung für Theoretische und Computergestützte Biophysik, Max-Planck-Institut für Biophysikalische Chemie, D-37077 Göttingen, Germany
| | - Andreas Russek
- Abteilung für Theoretische und Computergestützte Biophysik, Max-Planck-Institut für Biophysikalische Chemie, D-37077 Göttingen, Germany
| | - Piotr Neumann
- Abteilung für Molekulare Strukturbiologie, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften, Georg-August-Universität Göttingen, D-37077 Göttingen, Germany
| | - Emma Thomson
- Biochemie-Zentrum der Universität Heidelberg, D-69120 Heidelberg, Germany
| | - Ed Hurt
- Biochemie-Zentrum der Universität Heidelberg, D-69120 Heidelberg, Germany
| | - Ulrich Zachariae
- Scottish Universities' Physics Alliance, School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom; and
| | - Holger Stark
- Dreidimensionale Kryo-Elektronenmikroskopie, Max-Planck-Institut für Biophysikalische Chemie, D-37077 Göttingen, Germany
- Abteilung für Molekulare Kryo-Elektronenmikroskopie, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften, Georg-August-Universität Göttingen, D-37077 Göttingen, Germany
| | - Helmut Grubmüller
- Abteilung für Theoretische und Computergestützte Biophysik, Max-Planck-Institut für Biophysikalische Chemie, D-37077 Göttingen, Germany
| | - Achim Dickmanns
- Abteilung für Molekulare Strukturbiologie, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften, Georg-August-Universität Göttingen, D-37077 Göttingen, Germany
| | - Ralf Ficner
- Abteilung für Molekulare Strukturbiologie, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften, Georg-August-Universität Göttingen, D-37077 Göttingen, Germany
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21
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Koyama M, Matsuura Y. Mechanistic insights from the recent structures of the CRM1 nuclear export complex and its disassembly intermediate. Biophysics (Nagoya-shi) 2012; 8:145-50. [PMID: 27493531 PMCID: PMC4629651 DOI: 10.2142/biophysics.8.145] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2012] [Accepted: 10/16/2012] [Indexed: 01/04/2023] Open
Abstract
CRM1 (also known as exportin 1 or Xpo1) is the most versatile nuclear export receptor (exportin) that carries a broad range of proteins and ribonucleoproteins from the nucleus to the cytoplasm through the nuclear pore complex. The majority of the export substrates of CRM1 contain a short peptide sequence, so-called leucine-rich nuclear export signal (NES), which typically harbor four or five characteristically spaced hydrophobic residues. The transport directionality is determined by the small GTPase Ran and Ran-binding proteins that control the binding and dissociation of cargo. Here we review recent structural studies that advanced understanding of how NES is specifically recognized by CRM1 in the nucleus, and how NES is rapidly dissociated from CRM1 in the cytoplasm.
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Affiliation(s)
- Masako Koyama
- Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Yoshiyuki Matsuura
- Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan; Structural Biology Research Center, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
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22
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23
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Ran-dependent nuclear export mediators: a structural perspective. EMBO J 2011; 30:3457-74. [PMID: 21878989 DOI: 10.1038/emboj.2011.287] [Citation(s) in RCA: 159] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2011] [Accepted: 07/22/2011] [Indexed: 12/25/2022] Open
Abstract
Nuclear export is an essential eukaryotic activity. It proceeds through nuclear pore complexes (NPCs) and is mediated by soluble receptors that shuttle between nucleus and cytoplasm. RanGTPase-dependent export mediators (exportins) constitute the largest class of these carriers and are functionally highly versatile. All of these exportins load their substrates in response to RanGTP binding in the nucleus and traverse NPCs as ternary RanGTP-exportin-cargo complexes to the cytoplasm, where GTP hydrolysis leads to export complex disassembly. The different exportins vary greatly in their substrate range. Recent structural studies of both protein- and RNA-specific exporters have illuminated how exportins bind their cargoes, how Ran triggers cargo loading and how export complexes are disassembled in the cytoplasm. Here, we review the current state of knowledge and highlight emerging principles as well as prevailing questions.
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