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Gao X, Zhu K, Qin B, Olieric V, Wang M, Cui S. Crystal structure of SARS-CoV-2 Orf9b in complex with human TOM70 suggests unusual virus-host interactions. Nat Commun 2021; 12:2843. [PMID: 33990585 PMCID: PMC8121815 DOI: 10.1038/s41467-021-23118-8] [Citation(s) in RCA: 60] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Accepted: 04/16/2021] [Indexed: 12/11/2022] Open
Abstract
Although the accessory proteins are considered non-essential for coronavirus replication, accumulating evidences demonstrate they are critical to virus-host interaction and pathogenesis. Orf9b is a unique accessory protein of SARS-CoV-2 and SARS-CoV. It is implicated in immune evasion by targeting mitochondria, where it associates with the versatile adapter TOM70. Here, we determined the crystal structure of SARS-CoV-2 orf9b in complex with the cytosolic segment of human TOM70 to 2.2 Å. A central portion of orf9b occupies the deep pocket in the TOM70 C-terminal domain (CTD) and adopts a helical conformation strikingly different from the β-sheet-rich structure of the orf9b homodimer. Interactions between orf9b and TOM70 CTD are primarily hydrophobic and distinct from the electrostatic interaction between the heat shock protein 90 (Hsp90) EEVD motif and the TOM70 N-terminal domain (NTD). Using isothermal titration calorimetry (ITC), we demonstrated that the orf9b dimer does not bind TOM70, but a synthetic peptide harboring a segment of orf9b (denoted C-peptide) binds TOM70 with nanomolar KD. While the interaction between C-peptide and TOM70 CTD is an endothermic process, the interaction between Hsp90 EEVD and TOM70 NTD is exothermic, which underscores the distinct binding mechanisms at NTD and CTD pockets. Strikingly, the binding affinity of Hsp90 EEVD motif to TOM70 NTD is reduced by ~29-fold when orf9b occupies the pocket of TOM70 CTD, supporting the hypothesis that orf9b allosterically inhibits the Hsp90/TOM70 interaction. Our findings shed light on the mechanism underlying SARS-CoV-2 orf9b mediated suppression of interferon responses.
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Affiliation(s)
- Xiaopan Gao
- NHC Key Laboratory of Systems Biology of Pathogens, Institute of Pathogen Biology, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
- Sanming Project of Medicine in Shenzhen, National Clinical Research Center for Infectious Diseases, Shenzhen Third People's Hospital, Southern University of Science and Technology, Shenzhen, China
| | - Kaixiang Zhu
- NHC Key Laboratory of Systems Biology of Pathogens, Institute of Pathogen Biology, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Bo Qin
- NHC Key Laboratory of Systems Biology of Pathogens, Institute of Pathogen Biology, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
- Sanming Project of Medicine in Shenzhen, National Clinical Research Center for Infectious Diseases, Shenzhen Third People's Hospital, Southern University of Science and Technology, Shenzhen, China
| | - Vincent Olieric
- Swiss Light Source Paul Scherrer Institut, Villigen, PSI, Switzerland
| | - Meitian Wang
- Swiss Light Source Paul Scherrer Institut, Villigen, PSI, Switzerland
| | - Sheng Cui
- NHC Key Laboratory of Systems Biology of Pathogens, Institute of Pathogen Biology, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China.
- Sanming Project of Medicine in Shenzhen, National Clinical Research Center for Infectious Diseases, Shenzhen Third People's Hospital, Southern University of Science and Technology, Shenzhen, China.
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Kreimendahl S, Rassow J. The Mitochondrial Outer Membrane Protein Tom70-Mediator in Protein Traffic, Membrane Contact Sites and Innate Immunity. Int J Mol Sci 2020; 21:E7262. [PMID: 33019591 PMCID: PMC7583919 DOI: 10.3390/ijms21197262] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2020] [Revised: 09/25/2020] [Accepted: 09/28/2020] [Indexed: 02/08/2023] Open
Abstract
Tom70 is a versatile adaptor protein of 70 kDa anchored in the outer membrane of mitochondria in metazoa, fungi and amoeba. The tertiary structure was resolved for the Tom70 of yeast, showing 26 α-helices, most of them participating in the formation of 11 tetratricopeptide repeat (TPR) motifs. Tom70 serves as a docking site for cytosolic chaperone proteins and co-chaperones and is thereby involved in the uptake of newly synthesized chaperone-bound proteins in mitochondrial biogenesis. In yeast, Tom70 additionally mediates ER-mitochondria contacts via binding to sterol transporter Lam6/Ltc1. In mammalian cells, TOM70 promotes endoplasmic reticulum (ER) to mitochondria Ca2+ transfer by association with the inositol-1,4,5-triphosphate receptor type 3 (IP3R3). TOM70 is specifically targeted by the Bcl-2-related protein MCL-1 that acts as an anti-apoptotic protein in macrophages infected by intracellular pathogens, but also in many cancer cells. By participating in the recruitment of PINK1 and the E3 ubiquitin ligase Parkin, TOM70 can be implicated in the development of Parkinson's disease. TOM70 acts as receptor of the mitochondrial antiviral-signaling protein (MAVS) and thereby participates in the corresponding system of innate immunity against viral infections. The protein encoded by Orf9b in the genome of SARS-CoV-2 binds to TOM70, probably compromising the synthesis of type I interferons.
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Affiliation(s)
| | - Joachim Rassow
- Institute for Biochemistry and Pathobiochemistry, Ruhr-University Bochum, 44801 Bochum, Germany;
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Vignesh R, Aradhyam GK. A Change in Domain Cooperativity Drives the Function of Calnuc. Biochemistry 2020; 59:2507-2517. [PMID: 32543177 DOI: 10.1021/acs.biochem.0c00207] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
With the increasing incidence of neurodegenerative disorders, there is an urgent need to understand the protein folding process. Examining the folding process of multidomain proteins remains a prime challenge, as their complex conformational dynamics make them highly susceptible to misfolding and/or aggregation. The presence of multiple domains in a protein can lead to interaction between the partially folded domains, thereby driving misfolding and/or aggregation. Calnuc is one such multidomain protein for which Ca2+ binding plays a pivotal role in governing its structural dynamics and stability and, presumably, in directing its interactions with other proteins. We demonstrate differential structural dynamics between the Ca2+-free and Ca2+-bound forms of calnuc. In the absence of Ca2+, full-length calnuc displays equilibrium structural transitions with four intermediate states, reporting a sum of the behavioral properties of its individual domains. Fragment-based studies illustrate the sequential events of structure adoption proceeding in the following order: EF domain followed by the NT and LZ domains in the apo state. On the other hand, Ca2+ binding increases domain cooperativity and enables the protein to fold as a single unit. Single-tryptophan mutant proteins, designed in a domain-dependent manner, confirm an increase in the number of interdomain interactions in the Ca2+-bound form as compared to the Ca2+-free state of the protein, thereby providing insight into its folding process. The attenuated domain crosstalk in apo-calnuc is likely to influence and regulate its physiologically important intermolecular interactions.
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Affiliation(s)
- Ravichandran Vignesh
- Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai 600036, India
| | - Gopala Krishna Aradhyam
- Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai 600036, India
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Fan AC, Young JC. Function of cytosolic chaperones in Tom70-mediated mitochondrial import. Protein Pept Lett 2011; 18:122-31. [PMID: 20955164 PMCID: PMC5026486 DOI: 10.2174/092986611794475020] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2010] [Accepted: 09/17/2010] [Indexed: 11/22/2022]
Abstract
The great majority of mitochondrial proteins are synthesized by cytosolic ribosomes and then imported into the organelle post-translationally. The translocase of the outer membrane (TOM) is a proteinaceous machinery that contains surface receptors for preprotein recognition and also serves as the main entry gateway into mitochondria. Mitochondrial targeting requires various cytosolic factors, in particular the molecular chaperones Hsc70/Hsp70 and Hsp90. The chaperone activity of Hsc70/Hsp70 and Hsp90 occurs in coordinated cycles of ATP hydrolysis and substrate binding, and is regulated by a number of co-chaperone proteins. The import receptor Tom70 is a member of the tetratricopeptide repeat (TPR) co-chaperone family and contains a conserved TPR clamp domain for interaction with Hsc70 and Hsp90. Such interaction is essential for the initiation of the import process. This review will discuss the roles of Hsc70 and Hsp90 in mitochondrial import and summarize recent progress in understanding these pathways.
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Affiliation(s)
- Anna C.Y. Fan
- Department of Biochemistry, McGill University, 3649 Promenade Sir William Osler, Montreal, Quebec, Canada, H3G 0B1; Groupe de Recherche Axé sur la Structure des Protéines (GRASP)
| | - Jason C. Young
- Department of Biochemistry, McGill University, 3649 Promenade Sir William Osler, Montreal, Quebec, Canada, H3G 0B1; Groupe de Recherche Axé sur la Structure des Protéines (GRASP)
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Fan ACY, Gava LM, Ramos CHI, Young JC. Human mitochondrial import receptor Tom70 functions as a monomer. Biochem J 2010; 429:553-63. [PMID: 20504278 PMCID: PMC5026490 DOI: 10.1042/bj20091855] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The mitochondrial import receptor Tom70 (translocase of the mitochondrial outer membrane 70) interacts with chaperone-preprotein complexes through two domains: one that binds Hsp70 (heat-shock protein 70)/Hsc70 (heat-shock cognate 70) and Hsp90, and a second that binds preproteins. The oligomeric state of Tom70 has been controversial, with evidence for both monomeric and homodimeric forms. In the present paper, we report that the functional state of human Tom70 appears to be a monomer with mechanistic implications for its function in mitochondrial protein import. Based on analytical ultracentrifugation, cross-linking, size-exclusion chromatography and multi-angle light scattering, we found that the soluble cytosolic fragment of human Tom70 exists in equilibrium between monomer and dimer. A point mutation introduced at the predicted dimer interface increased the percentage of monomeric Tom70. Although chaperone docking to the mutant was the same as to the wild-type, the mutant was significantly more active in preprotein targeting. Cross-linking also demonstrated that the mutant formed stronger contacts with preprotein. However, cross-linking of full-length wild-type Tom70 on the mitochondrial membrane showed little evidence of homodimers. These results indicate that the Tom70 monomers are the functional form of the receptor, whereas the homodimers appear to be a minor population, and may represent an inactive state.
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Affiliation(s)
- Anna C. Y. Fan
- Department of Biochemistry, McGill University, 3649 Promenade Sir William Osler, Montreal, Quebec, Canada H3G 0B1
| | - Lisandra M. Gava
- Institute of Chemistry, University of Campinas (UNICAMP), Campinas, SP, Brazil
- Institute of Biology, University of Campinas (UNICAMP), Campinas, SP 13083-970, Brazil
| | - Carlos H. I. Ramos
- Institute of Chemistry, University of Campinas (UNICAMP), Campinas, SP, Brazil
| | - Jason C. Young
- Department of Biochemistry, McGill University, 3649 Promenade Sir William Osler, Montreal, Quebec, Canada H3G 0B1
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Abstract
The susceptibility of monoclonal antibodies (mAbs) to undergo cold denaturation remains unexplored. In this study, the phenomenon of cold denaturation was investigated for a mAb, mAb1, through thermodynamic and spectroscopic analyses. Tryptophan fluorescence and circular dichroism (CD) spectra were recorded for the guanidine hydrochloride (GuHCl)-induced unfolding of mAb1 at pH 6.3 at temperatures ranging from -5 to 50 degrees C. A three-state unfolding model incorporating the linear extrapolation method was fit to the fluorescence data to obtain an apparent free energy of unfolding, DeltaG(u), at each temperature. CD studies revealed that mAb1 exhibited polyproline II helical structure at low temperatures and at high GuHCl concentrations. The Gibbs-Helmholtz expression fit to the DeltaG(u) versus temperature data from fluorescence gave a DeltaC(p) of 8.0 kcal mol(-1) K(-1), a maximum apparent stability of 23.7 kcal mol(-1) at 18 degrees C, and an apparent cold denaturation temperature (T(CD)) of -23 degrees C. DeltaG(u) values for another mAb (mAb2) with a similar framework exhibited less stability at low temperatures, suggesting a depressed protein stability curve and a higher relative T(CD). Direct experimental evidence of the susceptibility of mAb1 and mAb2 to undergo cold denaturation in the absence of denaturant was confirmed at pH 2.5. Thus, mAbs have a potential to undergo cold denaturation at storage temperatures near -20 degrees C (pH 6.3), and this potential needs to be evaluated independently for individual mAbs.
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Affiliation(s)
- Kristi L Lazar
- Early Stage Pharmaceutical Development, Genentech, Inc., San Francisco, CA, USA
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Mills RD, Trewhella J, Qiu TW, Welte T, Ryan TM, Hanley T, Knott RB, Lithgow T, Mulhern TD. Domain Organization of the Monomeric Form of the Tom70 Mitochondrial Import Receptor. J Mol Biol 2009; 388:1043-58. [DOI: 10.1016/j.jmb.2009.03.070] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2009] [Revised: 03/24/2009] [Accepted: 03/30/2009] [Indexed: 11/28/2022]
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Perry AJ, Rimmer KA, Mertens HDT, Waller RF, Mulhern TD, Lithgow T, Gooley PR. Structure, topology and function of the translocase of the outer membrane of mitochondria. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2008; 46:265-74. [PMID: 18272380 DOI: 10.1016/j.plaphy.2007.12.012] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2007] [Indexed: 05/09/2023]
Abstract
Proteins destined for the mitochondria required the evolution of specific and efficient molecular machinery for protein import. The subunits of the import translocases of the inner membrane (TIM) appear homologous and conserved amongst species, however the components of the translocase of the outer membrane (TOM) show extensive differences between species. Recently, bioinformatic and structural analysis of Tom20, an important receptor subunit of the TOM complex, suggests that this protein complex arose from different ancestors for plants compared to animals and fungi, but has subsequently converged to provide similar functions and analogous structures. Here we review the current knowledge of the TOM complex, the function and structure of the various subunits that make up this molecular machine.
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Affiliation(s)
- Andrew J Perry
- Department of Biochemistry and Molecular Biology, Bio21 Institute of Biotechnology and Molecular Science, University of Melbourne, Parkville, Victoria 3010, Australia
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