1
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Altenburg AF, Morley JL, Bauer J, Walz JS, Boyle LH. Reanalysis of Immunopeptidomics Datasets Provides Mechanistic Insight into TAPBPR-Mediated Peptide Editing on HLA-A, -B and -C Molecules. Wellcome Open Res 2024; 9:113. [PMID: 38800518 PMCID: PMC11126903 DOI: 10.12688/wellcomeopenres.20738.1] [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] [Accepted: 02/15/2024] [Indexed: 05/29/2024] Open
Abstract
Background Major histocompatibility class I (MHC-I, human leukocyte antigen [HLA]-I in humans) molecules present small fragments of the proteome on the cell surface for immunosurveillance, which is pivotal to control infected and malignant cells. Immunogenic peptides are generated and selected in the MHC-I antigen processing and presentation pathway. In this pathway, two homologous molecules, tapasin and TAPBPR, optimise the MHC-I peptide repertoire that is ultimately presented at the plasma membrane. Peptide exchange on HLA-I by human TAPBPR involves the flexible loop region K22-D35, with the leucine at position 30 (L30) involved in mediating peptide dissociation. However, our understanding of the exact molecular mechanisms governing TAPBPR-mediated peptide exchange on HLA-I allotypes remains incomplete. Methods Here, in-depth re-analyses of published immunopeptidomics datasets was used to further examine TAPBPR peptide editing activity and mechanism of action on HLA-I. The role of the TAPBPR editing loop in opening the HLA-I peptide binding groove was assessed using a molecular dynamics simulation. Results We show that TAPBPR shapes the peptide repertoire on HLA-A, -B and -C allotypes. The TAPBPR editing loop was not essential to allow HLA-I to adopt an open state. L30 in the TAPBPR editing loop was typically sufficient to mediate peptide repertoire restriction on the three HLA-I allotypes expressed by HeLa cells. TAPBPR was also able to load peptides onto HLA-I in a loop-dependent manner. Conclusions These results unify the previously hypothesised scoop loop and peptide trap mechanisms of TAPBPR-mediated peptide exchange, with the former involved in peptide filtering and the latter in peptide loading.
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Affiliation(s)
- Arwen F Altenburg
- Department of Pathology, University of Cambridge, Cambridge, England, CB2 1QP, UK
| | - Jack L Morley
- Department of Pathology, University of Cambridge, Cambridge, England, CB2 1QP, UK
| | - Jens Bauer
- Department of Peptide-based Immunotherapy, Institute of Immunology, University and University Hospital, Tübingen, Germany
- Cluster of Excellence iFIT (EXC2180) “Image-Guided and Functionally Instructed Tumor Therapies”, University of Tübingen, Tübingen, Germany
| | - Juliane S Walz
- Department of Peptide-based Immunotherapy, Institute of Immunology, University and University Hospital, Tübingen, Germany
- Cluster of Excellence iFIT (EXC2180) “Image-Guided and Functionally Instructed Tumor Therapies”, University of Tübingen, Tübingen, Germany
- Clinical Collaboration Unit Translational Immunology, German Cancer Consortium (DKTK), Department of Internal Medicine, University Hospital Tübingen, Tübingen, Germany
| | - Louise H Boyle
- Department of Pathology, University of Cambridge, Cambridge, England, CB2 1QP, UK
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2
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Czaja AJ. Introducing Molecular Chaperones into the Causality and Prospective Management of Autoimmune Hepatitis. Dig Dis Sci 2023; 68:4098-4116. [PMID: 37755606 PMCID: PMC10570239 DOI: 10.1007/s10620-023-08118-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/02/2023] [Accepted: 09/18/2023] [Indexed: 09/28/2023]
Abstract
Molecular chaperones influence the immunogenicity of peptides and the activation of effector T cells, and their pathogenic roles in autoimmune hepatitis are unclear. Heat shock proteins are pivotal in the processing and presentation of peptides that activate CD8+ T cells. They can also induce regulatory B and T cells and promote immune tolerance. Tapasin and the transporter associated with antigen processing-binding protein influence the editing and loading of high-affinity peptides for presentation by class I molecules of the major histocompatibility complex. Their over-expression could enhance the autoimmune response, and their deficiency could weaken it. The lysosome-associated membrane protein-2a isoform in conjunction with heat shock cognate 70 supports the importation of cytosolic proteins into lysosomes. Chaperone-mediated autophagy can then process the peptides for activation of CD4+ T cells. Over-expression of autophagy in T cells may also eliminate negative regulators of their activity. The human leukocyte antigen B-associated transcript three facilitates the expression of class II peptide receptors, inhibits T cell apoptosis, prevents T cell exhaustion, and sustains the immune response. Immunization with heat shock proteins has induced immune tolerance in experimental models and humans with autoimmune disease by inducing regulatory T cells. Therapeutic manipulation of other molecular chaperones may promote T cell exhaustion and induce tolerogenic dendritic cells. In conclusion, molecular chaperones constitute an under-evaluated family of ancillary proteins that could affect the occurrence, severity, and outcome of autoimmune hepatitis. Clarification of their contributions to the immune mechanisms and clinical activity of autoimmune hepatitis could have therapeutic implications.
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Affiliation(s)
- Albert J Czaja
- Mayo Clinic College of Medicine and Science, 200 First Street S.W., Rochester, MN, 55905, USA.
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3
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Li L, Peng X, Batliwala M, Bouvier M. Crystal structures of MHC class I complexes reveal the elusive intermediate conformations explored during peptide editing. Nat Commun 2023; 14:5020. [PMID: 37596268 PMCID: PMC10439229 DOI: 10.1038/s41467-023-40736-6] [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: 01/20/2023] [Accepted: 08/08/2023] [Indexed: 08/20/2023] Open
Abstract
Studies have suggested that MHC class I (MHC I) molecules fluctuate rapidly between numerous conformational states and these motions support peptide sampling. To date, MHC I intermediates are largely uncharacterized experimentally and remain elusive. Here, we present x-ray crystal structures of HLA-B8 loaded with 20mer peptides that show pronounced distortions at the N-terminus of the groove. Long stretches of N-terminal amino acid residues are missing in the electron density maps creating an open-ended groove. Our structures also reveal highly unusual features in MHC I-peptide interaction at the N-terminus of the groove. Molecular dynamics simulations indicate that the complexes have varying degrees of conformational flexibility in a manner consistent with the structures. We suggest that our structures have captured the remarkable molecular dynamics of MHC I-peptide interaction. The visualization of peptide-dependent conformational motions in MHC I is a major step forward in our conceptual understanding of dynamics in high-affinity peptide selection.
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Affiliation(s)
- Lenong Li
- Department of Microbiology and Immunology, University of Illinois, Chicago, IL, 60612, USA
| | - Xubiao Peng
- Center for Quantum Technology Research and Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurements, School of Physics, Beijing Institute of Technology, Beijing, 100081, China
| | - Mansoor Batliwala
- Department of Microbiology and Immunology, University of Illinois, Chicago, IL, 60612, USA
| | - Marlene Bouvier
- Department of Microbiology and Immunology, University of Illinois, Chicago, IL, 60612, USA.
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4
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Sun Y, Young MC, Woodward CH, Danon JN, Truong HV, Gupta S, Winters TJ, Font-Burgada J, Burslem GM, Sgourakis NG. Universal open MHC-I molecules for rapid peptide loading and enhanced complex stability across HLA allotypes. Proc Natl Acad Sci U S A 2023; 120:e2304055120. [PMID: 37310998 PMCID: PMC10288639 DOI: 10.1073/pnas.2304055120] [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: 03/10/2023] [Accepted: 05/18/2023] [Indexed: 06/15/2023] Open
Abstract
The polymorphic nature and intrinsic instability of class I major histocompatibility complex (MHC-I) and MHC-like molecules loaded with suboptimal peptides, metabolites, or glycolipids presents a fundamental challenge for identifying disease-relevant antigens and antigen-specific T cell receptors (TCRs), hindering the development of autologous therapeutics. Here, we leverage the positive allosteric coupling between the peptide and light chain (β2 microglobulin, β2m) subunits for binding to the MHC-I heavy chain (HC) through an engineered disulfide bond bridging conserved epitopes across the HC/β2m interface, to generate conformationally stable, peptide-receptive molecules named "open MHC-I." Biophysical characterization shows that open MHC-I molecules are properly folded protein complexes of enhanced thermal stability compared to the wild type when loaded with low- to moderate-affinity peptides. Using solution NMR, we characterize the effects of the disulfide bond on the conformation and dynamics of the MHC-I structure, ranging from local changes in β2m-interacting sites of the peptide-binding groove to long-range effects on the α2-1 helix and α3 domain. The interchain disulfide bond stabilizes MHC-I molecules in an open conformation to promote peptide exchange across multiple human leukocyte antigen (HLA) allotypes, covering representatives from five HLA-A supertypes, six HLA-B supertypes, and oligomorphic HLA-Ib molecules. Our structure-guided design, combined with conditional β-peptide ligands, provides a universal platform to generate ready-to-load MHC-I systems of enhanced stability, enabling a range of approaches to screen antigenic epitope libraries and probe polyclonal TCR repertoires covering highly polymorphic HLA-I allotypes, as well as oligomorphic nonclassical molecules.
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Affiliation(s)
- Yi Sun
- Center for Computational and Genomic Medicine, Department of Pathology and Laboratory Medicine, The Children’s Hospital of Philadelphia, Philadelphia, PA19104
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA19104
| | - Michael C. Young
- Center for Computational and Genomic Medicine, Department of Pathology and Laboratory Medicine, The Children’s Hospital of Philadelphia, Philadelphia, PA19104
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA19104
| | - Claire H. Woodward
- Center for Computational and Genomic Medicine, Department of Pathology and Laboratory Medicine, The Children’s Hospital of Philadelphia, Philadelphia, PA19104
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA19104
| | - Julia N. Danon
- Center for Computational and Genomic Medicine, Department of Pathology and Laboratory Medicine, The Children’s Hospital of Philadelphia, Philadelphia, PA19104
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA19104
| | - Hau V. Truong
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA19104
| | - Sagar Gupta
- Center for Computational and Genomic Medicine, Department of Pathology and Laboratory Medicine, The Children’s Hospital of Philadelphia, Philadelphia, PA19104
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA19104
| | - Trenton J. Winters
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA19104
| | - Joan Font-Burgada
- Cancer Signaling and Microenvironment Program, Fox Chase Cancer Center, Philadelphia, PA19111
| | - George M. Burslem
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA19104
- Department of Cancer Biology and Epigenetics Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA19104
| | - Nikolaos G. Sgourakis
- Center for Computational and Genomic Medicine, Department of Pathology and Laboratory Medicine, The Children’s Hospital of Philadelphia, Philadelphia, PA19104
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA19104
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5
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Margulies DH, Jiang J, Ahmad J, Boyd LF, Natarajan K. Chaperone function in antigen presentation by MHC class I molecules-tapasin in the PLC and TAPBPR beyond. Front Immunol 2023; 14:1179846. [PMID: 37398669 PMCID: PMC10308438 DOI: 10.3389/fimmu.2023.1179846] [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: 03/05/2023] [Accepted: 05/30/2023] [Indexed: 07/04/2023] Open
Abstract
Peptide loading of MHC-I molecules plays a critical role in the T cell response to infections and tumors as well as to interactions with inhibitory receptors on natural killer (NK) cells. To facilitate and optimize peptide acquisition, vertebrates have evolved specialized chaperones to stabilize MHC-I molecules during their biosynthesis and to catalyze peptide exchange favoring high affinity or optimal peptides to permit transport to the cell surface where stable peptide/MHC-I (pMHC-I) complexes are displayed and are available for interaction with T cell receptors and any of a host of inhibitory and activating receptors. Although components of the endoplasmic reticulum (ER) resident peptide loading complex (PLC) were identified some 30 years ago, the detailed biophysical parameters that govern peptide selection, binding, and surface display have recently been understood better with advances in structural methods including X-ray crystallography, cryogenic electron microscopy (cryo-EM), and computational modeling. These approaches have provided refined mechanistic illustration of the molecular events involved in the folding of the MHC-I heavy chain, its coordinate glycosylation, assembly with its light chain, β2-microglobulin (β2m), its association with the PLC, and its binding of peptides. Our current view of this important cellular process as it relates to antigen presentation to CD8+ T cells is based on many different approaches: biochemical, genetic, structural, computational, cell biological, and immunological. In this review, taking advantage of recent X-ray and cryo-EM structural evidence and molecular dynamics simulations, examined in the context of past experiments, we attempt a dispassionate evaluation of the details of peptide loading in the MHC-I pathway. By critical evaluation of several decades of investigation, we outline aspects of the peptide loading process that are well-understood and indicate those that demand further detailed investigation. Further studies should contribute not only to basic understanding, but also to applications for immunization and therapy of tumors and infections.
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6
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Satti R, Morley JL, Boyle LH. Get into the groove! The influence of TAPBPR on cargo selection. Curr Opin Immunol 2023; 83:102346. [PMID: 37295041 DOI: 10.1016/j.coi.2023.102346] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2022] [Revised: 04/28/2023] [Accepted: 05/02/2023] [Indexed: 06/12/2023]
Abstract
Since the discovery of Transporter associated with antigen processing-binding protein-related (TAPBPR) over two decades ago, extensive studies have explored its function in the context of the major histocompatibility complex class-I (MHC-I) antigen processing and presentation pathway. As a chaperone and peptide editor, TAPBPR was recently revealed to have overlapping structural features when resolved with peptide-receptive MHC-I molecules compared with the two newly solved tapasin:MHC-I structures. Despite this, the two chaperones seem to have a unique criteria for loading high-affinity peptides on MHC-I molecules. Yet, the mechanism of action of how TAPBPR creates its distinct filter in cargo selection for peptide-receptive MHC-I molecules continues to be a subject of debate.
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Affiliation(s)
- Reem Satti
- Department of Pathology, University of Cambridge, Cambridge CB2 1QP , UK
| | - Jack L Morley
- Department of Pathology, University of Cambridge, Cambridge CB2 1QP , UK
| | - Louise H Boyle
- Department of Pathology, University of Cambridge, Cambridge CB2 1QP , UK.
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7
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Sun Y, Young MC, Woodward CH, Danon JN, Truong H, Gupta S, Winters TJ, Burslem G, Sgourakis NG. Universal open MHC-I molecules for rapid peptide loading and enhanced complex stability across HLA allotypes. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.18.533266. [PMID: 36993702 PMCID: PMC10055308 DOI: 10.1101/2023.03.18.533266] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The polymorphic nature and intrinsic instability of class I major histocompatibility complex (MHC-I) and MHC-like molecules loaded with suboptimal peptides, metabolites, or glycolipids presents a fundamental challenge for identifying disease-relevant antigens and antigen-specific T cell receptors (TCRs), hindering the development of autologous therapeutics. Here, we leverage the positive allosteric coupling between the peptide and light chain (β 2 microglobulin, β 2 m) subunits for binding to the MHC-I heavy chain (HC) through an engineered disulfide bond bridging conserved epitopes across the HC/β 2 m interface, to generate conformationally stable, open MHC-I molecules. Biophysical characterization shows that open MHC-I molecules are properly folded protein complexes of enhanced thermal stability compared to the wild type, when loaded with low- to intermediate-affinity peptides. Using solution NMR, we characterize the effects of the disulfide bond on the conformation and dynamics of the MHC-I structure, ranging from local changes in β 2 m interacting sites of the peptide binding groove to long-range effects on the α 2-1 helix and α 3 domain. The interchain disulfide bond stabilizes empty MHC-I molecules in a peptide-receptive, open conformation to promote peptide exchange across multiple human leucocyte antigen (HLA) allotypes, covering representatives from five HLA-A, six HLA-B supertypes, and oligomorphic HLA-Ib molecules. Our structural design, combined with conditional β-peptide ligands, provides a universal platform for generating ready-to-load MHC-I systems of enhanced stability, enabling a range of approaches to screen antigenic epitope libraries and probe polyclonal TCR repertoires in the context of highly polymorphic HLA-I allotypes, as well as oligomorphic nonclassical molecules. Significance Statement We outline a structure-guided approach for generating conformationally stable, open MHC-I molecules with enhanced ligand exchange kinetics spanning five HLA-A, all HLA-B supertypes, and oligomorphic HLA-Ib allotypes. We present direct evidence of positive allosteric cooperativity between peptide binding and β 2 m association with the heavy chain by solution NMR and HDX-MS spectroscopy. We demonstrate that covalently linked β 2 m serves as a conformational chaperone to stabilize empty MHC-I molecules in a peptide-receptive state, by inducing an open conformation and preventing intrinsically unstable heterodimers from irreversible aggregation. Our study provides structural and biophysical insights into the conformational properties of MHC-I ternary complexes, which can be further applied to improve the design of ultra-stable, universal ligand exchange systems in a pan-HLA allelic setting.
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8
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Sun Y, Papadaki GF, Devlin CA, Danon JN, Young MC, Winters TJ, Burslem GM, Procko E, Sgourakis NG. Xeno interactions between MHC-I proteins and molecular chaperones enable ligand exchange on a broad repertoire of HLA allotypes. SCIENCE ADVANCES 2023; 9:eade7151. [PMID: 36827371 PMCID: PMC9956121 DOI: 10.1126/sciadv.ade7151] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2022] [Accepted: 01/19/2023] [Indexed: 06/01/2023]
Abstract
Immunological chaperones tapasin and TAP binding protein, related (TAPBPR) play key roles in antigenic peptide optimization and quality control of nascent class I major histocompatibility complex (MHC-I) molecules. The polymorphic nature of MHC-I proteins leads to a range of allelic dependencies on chaperones for assembly and cell-surface expression, limiting chaperone-mediated peptide exchange to a restricted set of human leukocyte antigen (HLA) allotypes. Here, we demonstrate and characterize xeno interactions between a chicken TAPBPR ortholog and a complementary repertoire of HLA allotypes, relative to its human counterpart. We find that TAPBPR orthologs recognize empty MHC-I with broader allele specificity and facilitate peptide exchange by maintaining a reservoir of receptive molecules. Deep mutational scanning of human TAPBPR further identifies gain-of-function mutants, resembling the chicken sequence, which can enhance HLA-A*01:01 expression in situ and promote peptide exchange in vitro. These results highlight that polymorphic sites on MHC-I and chaperone surfaces can be engineered to manipulate their interactions, enabling chaperone-mediated peptide exchange on disease-relevant HLA alleles.
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Affiliation(s)
- Yi Sun
- Department of Pathology and Laboratory Medicine, Children’s Hospital of Philadelphia, Philadelphia, PA 19104, USA
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, 3501 Civic Center Blvd., Philadelphia, PA 19104, USA
| | - Georgia F. Papadaki
- Department of Pathology and Laboratory Medicine, Children’s Hospital of Philadelphia, Philadelphia, PA 19104, USA
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, 3501 Civic Center Blvd., Philadelphia, PA 19104, USA
| | - Christine A. Devlin
- Department of Biochemistry and Cancer Center at Illinois, University of Illinois, Urbana, IL 61820, USA
| | - Julia N. Danon
- Department of Pathology and Laboratory Medicine, Children’s Hospital of Philadelphia, Philadelphia, PA 19104, USA
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, 3501 Civic Center Blvd., Philadelphia, PA 19104, USA
| | - Michael C. Young
- Department of Pathology and Laboratory Medicine, Children’s Hospital of Philadelphia, Philadelphia, PA 19104, USA
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, 3501 Civic Center Blvd., Philadelphia, PA 19104, USA
| | - Trenton J. Winters
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, 3501 Civic Center Blvd., Philadelphia, PA 19104, USA
| | - George M. Burslem
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, 3501 Civic Center Blvd., Philadelphia, PA 19104, USA
- Department of Cancer Biology and Epigenetics Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Erik Procko
- Department of Biochemistry and Cancer Center at Illinois, University of Illinois, Urbana, IL 61820, USA
| | - Nikolaos G. Sgourakis
- Department of Pathology and Laboratory Medicine, Children’s Hospital of Philadelphia, Philadelphia, PA 19104, USA
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, 3501 Civic Center Blvd., Philadelphia, PA 19104, USA
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9
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Li L, Peng X, Batliwala M, Bouvier M. Unusual crystal structures of MHC class I complexes reveal the elusive intermediate conformations explored during peptide editing in antigen presentation. RESEARCH SQUARE 2023:rs.3.rs-2500847. [PMID: 36747752 PMCID: PMC9901037 DOI: 10.21203/rs.3.rs-2500847/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Studies have suggested that MHC class I (MHC I) molecules fluctuate rapidly between conformational states as they sample peptides for potential ligands. To date, MHC I intermediates are largely uncharacterized experimentally and remain elusive. We present x-ray crystal structures of HLA-B8 loaded with 20mer peptides that show significant conformational heterogeneity at the N-terminus of the groove. Long stretches of N-terminal residues were missing in the electron density maps creating an unstructured and widely open-ended groove. Our structures also revealed highly unusual features in MHC I and peptide conformations, and in MHC I-peptide interaction at the N-terminus of the groove. Molecular dynamics simulations showed that the complexes have varying degrees of flexibility in a manner consistent with the structures. We suggest that our structures represent transient substates explored by MHC I molecules during peptide editing. The visualization of peptide-dependent conformational flexibility in MHC I groove is a major step forward in our conceptual understanding of peptide repertoire development in antigen presentation. Our study also raises questions about the role of the N-terminus of the groove in peptide editing.
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Affiliation(s)
- Lenong Li
- Department of Microbiology and Immunology, University of Illinois, Chicago, IL, 60612, USA
| | - Xubiao Peng
- Center for Quantum Technology Research and Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurements (MOE), School of Physics, Beijing Institute of Technology, Beijing 100081, China
| | - Mansoor Batliwala
- Department of Microbiology and Immunology, University of Illinois, Chicago, IL, 60612, USA
| | - Marlene Bouvier
- Department of Microbiology and Immunology, University of Illinois, Chicago, IL, 60612, USA
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10
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Müller IK, Winter C, Thomas C, Spaapen RM, Trowitzsch S, Tampé R. Structure of an MHC I–tapasin–ERp57 editing complex defines chaperone promiscuity. Nat Commun 2022; 13:5383. [PMID: 36104323 PMCID: PMC9474470 DOI: 10.1038/s41467-022-32841-9] [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: 02/09/2022] [Accepted: 08/19/2022] [Indexed: 11/24/2022] Open
Abstract
Adaptive immunity depends on cell surface presentation of antigenic peptides by major histocompatibility complex class I (MHC I) molecules and on stringent ER quality control in the secretory pathway. The chaperone tapasin in conjunction with the oxidoreductase ERp57 is crucial for MHC I assembly and for shaping the epitope repertoire for high immunogenicity. However, how the tapasin–ERp57 complex engages MHC I clients has not yet been determined at atomic detail. Here, we present the 2.7-Å crystal structure of a tapasin–ERp57 heterodimer in complex with peptide-receptive MHC I. Our study unveils molecular details of client recognition by the multichaperone complex and highlights elements indispensable for peptide proofreading. The structure of this transient ER quality control complex provides the mechanistic basis for the selector function of tapasin and showcases how the numerous MHC I allomorphs are chaperoned during peptide loading and editing. Adaptive immunity depends on cellular chaperone and quality control systems that are decisive for an effective presentation of foreign antigens via MHC I molecules. Here, the authors present the structure of a key chaperone-MHC I complex.
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11
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McShan AC, Devlin CA, Papadaki GF, Sun Y, Green AI, Morozov GI, Burslem GM, Procko E, Sgourakis NG. TAPBPR employs a ligand-independent docking mechanism to chaperone MR1 molecules. Nat Chem Biol 2022; 18:859-868. [PMID: 35725941 PMCID: PMC9703140 DOI: 10.1038/s41589-022-01049-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2021] [Accepted: 04/28/2022] [Indexed: 11/08/2022]
Abstract
Chaperones tapasin and transporter associated with antigen processing (TAP)-binding protein related (TAPBPR) associate with the major histocompatibility complex (MHC)-related protein 1 (MR1) to promote trafficking and cell surface expression. However, the binding mechanism and ligand dependency of MR1/chaperone interactions remain incompletely characterized. Here in vitro, biochemical and computational studies reveal that, unlike MHC-I, TAPBPR recognizes MR1 in a ligand-independent manner owing to the absence of major structural changes in the MR1 α2-1 helix between empty and ligand-loaded molecules. Structural characterization using paramagnetic nuclear magnetic resonance experiments combined with restrained molecular dynamics simulations reveals that TAPBPR engages conserved surfaces on MR1 to induce similar adaptations to those seen in MHC-I/TAPBPR co-crystal structures. Finally, nuclear magnetic resonance relaxation dispersion experiments using 19F-labeled diclofenac show that TAPBPR can affect the exchange kinetics of noncovalent metabolites with the MR1 groove, serving as a catalyst. Our results support a role of chaperones in stabilizing nascent MR1 molecules to enable loading of endogenous or exogenous cargo.
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Affiliation(s)
- Andrew C McShan
- Center for Computational and Genomic Medicine, Department of Pathology and Laboratory Medicine, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Christine A Devlin
- Department of Biochemistry and Cancer Center at Illinois, University of Illinois, Urbana, IL, USA
| | - Georgia F Papadaki
- Center for Computational and Genomic Medicine, Department of Pathology and Laboratory Medicine, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Yi Sun
- Center for Computational and Genomic Medicine, Department of Pathology and Laboratory Medicine, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Adam I Green
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Giora I Morozov
- Center for Computational and Genomic Medicine, Department of Pathology and Laboratory Medicine, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - George M Burslem
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
- Department of Cancer Biology and Epigenetics Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Erik Procko
- Department of Biochemistry and Cancer Center at Illinois, University of Illinois, Urbana, IL, USA
| | - Nikolaos G Sgourakis
- Center for Computational and Genomic Medicine, Department of Pathology and Laboratory Medicine, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
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12
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Xu H, Song K, Da LT. Dynamics of peptide loading into major histocompatibility complex class I molecules chaperoned by TAPBPR. Phys Chem Chem Phys 2022; 24:12397-12409. [PMID: 35575131 DOI: 10.1039/d2cp00423b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Major histocompatibility complex class I (MHC-I) molecules display antigenic peptides on the cell surface for T cell receptor scanning, thereby activating the immune response. Peptide loading into MHC-I molecules is thus a critical step during the antigen presentation process. Chaperone TAP-binding protein related (TAPBPR) plays a critical role in promoting high-affinity peptide loading into MHC-I, by discriminating against the low-affinity ones. However, the complete peptide loading dynamics into TAPBPR-bound MHC-I is still elusive. Here, we constructed kinetic network models based on hundreds of short-time MD simulations with an aggregated simulation time of ∼21.7 μs, and revealed, at atomic level, four key intermediate states of one antigenic peptide derived from melanoma-associated MART-1/Melan-A protein during its loading process into TAPBPR-bound MHC-I. We find that the TAPBPR binding at the MHC-I pocket-F can substantially reshape the distant pocket-B via allosteric regulations, which in turn promotes the following peptide N-terminal loading. Intriguingly, the partially loaded peptide could profoundly weaken the TAPBPR-MHC stability, promoting the dissociation of the TAPBPR scoop-loop (SL) region from the pocket-F to a more solvent-exposed conformation. Structural inspections further indicate that the peptide loading could remotely affect the SL binding site through both allosteric perturbations and direct contacts. In addition, another structural motif of TAPBPR, the jack hairpin region, was also found to participate in mediating the peptide editing. Our study sheds light on the detailed molecular mechanisms underlying the peptide loading process into TAPBPR-bound MHC-I and pinpoints the key structural factors responsible for dictating the peptide-loading dynamics.
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Affiliation(s)
- Honglin Xu
- Key Laboratory of Systems Biomedicine (Ministry of Education), Shanghai Center for Systems Biomedicine, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China.
| | - Kaiyuan Song
- Key Laboratory of Systems Biomedicine (Ministry of Education), Shanghai Center for Systems Biomedicine, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China.
| | - Lin-Tai Da
- Key Laboratory of Systems Biomedicine (Ministry of Education), Shanghai Center for Systems Biomedicine, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China.
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13
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Ilca FT, Boyle LH. The glycosylation status of MHC class I molecules impacts their interactions with TAPBPR. Mol Immunol 2021; 139:168-176. [PMID: 34543843 PMCID: PMC8524320 DOI: 10.1016/j.molimm.2021.09.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Revised: 05/16/2021] [Accepted: 09/11/2021] [Indexed: 11/20/2022]
Abstract
Glycosylation plays a crucial role in the folding, structure, quality control and trafficking of glycoproteins. Here, we explored whether the glycosylation status of MHC class I (MHC-I) molecules impacts their affinity for the peptide editor, TAPBPR. We demonstrate that the interaction between TAPBPR and MHC-I is stronger when MHC-I lacks a glycan. Subsequently, TAPBPR can dissociate peptides, even those of high affinity, more easily from non-glycosylated MHC-I compared to their glycosylated counterparts. In addition, TAPBPR is more resistant to peptide-mediated allosteric release from non-glycosylated MHC-I compared to species with a glycan attached. Consequently, we find the glycosylation status of HLA-A*68:02, -A*02:01 and -B*27:05 influences their ability to undergo TAPBPR-mediated peptide exchange. The discovery that the glycan attached to MHC-I significantly influences the affinity of their interactions with TAPBPR has important implications, on both an experimental level and in a biological context.
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Affiliation(s)
- F Tudor Ilca
- Department of Pathology, University of Cambridge, Cambridge, CB2 1QP, UK
| | - Louise H Boyle
- Department of Pathology, University of Cambridge, Cambridge, CB2 1QP, UK.
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14
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Lan H, Abualrous ET, Sticht J, Fernandez LMA, Werk T, Weise C, Ballaschk M, Schmieder P, Loll B, Freund C. Exchange catalysis by tapasin exploits conserved and allele-specific features of MHC-I molecules. Nat Commun 2021; 12:4236. [PMID: 34244493 PMCID: PMC8271027 DOI: 10.1038/s41467-021-24401-4] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Accepted: 06/18/2021] [Indexed: 11/29/2022] Open
Abstract
The repertoire of peptides presented by major histocompatibility complex class I (MHC-I) molecules on the cell surface is tailored by the ER-resident peptide loading complex (PLC), which contains the exchange catalyst tapasin. Tapasin stabilizes MHC-I molecules and promotes the formation of stable peptide-MHC-I (pMHC-I) complexes that serve as T cell antigens. Exchange of suboptimal by high-affinity ligands is catalyzed by tapasin, but the underlying mechanism is still elusive. Here we analyze the tapasin-induced changes in MHC-I dynamics, and find the catalyst to exploit two essential features of MHC-I. First, tapasin recognizes a conserved allosteric site underneath the α2-1-helix of MHC-I, ‘loosening’ the MHC-I F-pocket region that accomodates the C-terminus of the peptide. Second, the scoop loop11–20 of tapasin relies on residue L18 to target the MHC-I F-pocket, enabling peptide exchange. Meanwhile, tapasin residue K16 plays an accessory role in catalysis of MHC-I allotypes bearing an acidic F-pocket. Thus, our results provide an explanation for the observed allele-specificity of catalyzed peptide exchange. Tapasin is part of the peptide loading complex necessary for presenting antigenic peptides on MHC-I for the induction of adaptive immunity. Here the authors show that tapasin interacts with MHC-I in both conserved and allele-specific regions to promote antigen presentation, with tapasin L18 and K16 residues both implicated in this molecular interaction.
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Affiliation(s)
- Huan Lan
- Laboratory of Protein Biochemistry, Institute for Chemistry & Biochemistry, Freie Universität Berlin, Berlin, Germany
| | - Esam T Abualrous
- Laboratory of Protein Biochemistry, Institute for Chemistry & Biochemistry, Freie Universität Berlin, Berlin, Germany.,Artificial Intelligence for the Sciences, Department of Mathematics and Computer Science, Freie Universität Berlin, Berlin, Germany
| | - Jana Sticht
- Laboratory of Protein Biochemistry, Institute for Chemistry & Biochemistry, Freie Universität Berlin, Berlin, Germany.,Core Facility BioSupraMol, Institute for Chemistry & Biochemistry, Freie Universität Berlin, Berlin, Germany
| | - Laura Maria Arroyo Fernandez
- Laboratory of Protein Biochemistry, Institute for Chemistry & Biochemistry, Freie Universität Berlin, Berlin, Germany
| | - Tamina Werk
- Laboratory of Protein Biochemistry, Institute for Chemistry & Biochemistry, Freie Universität Berlin, Berlin, Germany
| | - Christoph Weise
- Laboratory of Protein Biochemistry, Institute for Chemistry & Biochemistry, Freie Universität Berlin, Berlin, Germany.,Core Facility BioSupraMol, Institute for Chemistry & Biochemistry, Freie Universität Berlin, Berlin, Germany
| | - Martin Ballaschk
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Berlin, Germany
| | - Peter Schmieder
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Berlin, Germany
| | - Bernhard Loll
- Laboratory of Structural Biology, Institute for Chemistry & Biochemistry, Freie Universität Berlin, Berlin, Germany
| | - Christian Freund
- Laboratory of Protein Biochemistry, Institute for Chemistry & Biochemistry, Freie Universität Berlin, Berlin, Germany.
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15
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Hafstrand I, Aflalo A, Boyle LH. Why TAPBPR? Implications of an additional player in MHC class I peptide presentation. Curr Opin Immunol 2021; 70:90-94. [PMID: 34052734 DOI: 10.1016/j.coi.2021.04.011] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Revised: 04/15/2021] [Accepted: 04/30/2021] [Indexed: 10/21/2022]
Abstract
The peptide editor TAPBPR is the newest member of the major histocompatibility complex class I (MHC-I) antigen processing and presentation pathway. Since 2013, studies have explored the functions and mechanisms of action of this tapasin homolog. Here, we review the key insights gained from structural studies of the TAPBPR:MHC-I complex and the involvement of the TAPBPR loop in peptide exchange. However, despite recent advances, the question still remains: why do we need TAPBPR? The recent appreciation that different MHC-I allotypes vary in their ability to interact with TAPBPR, together with a role for TAPBPR in alternative presentation pathways highlights that much remains unknown concerning the biological need for TAPBPR.
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Affiliation(s)
- Ida Hafstrand
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, United Kingdom; Cancer Research UK Cambridge Institute, University of Cambridge, Cambridge, United Kingdom
| | - Aure Aflalo
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, United Kingdom
| | - Louise H Boyle
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, United Kingdom.
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16
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McWilliam HEG, Mak JYW, Awad W, Zorkau M, Cruz-Gomez S, Lim HJ, Yan Y, Wormald S, Dagley LF, Eckle SBG, Corbett AJ, Liu H, Li S, Reddiex SJJ, Mintern JD, Liu L, McCluskey J, Rossjohn J, Fairlie DP, Villadangos JA. Endoplasmic reticulum chaperones stabilize ligand-receptive MR1 molecules for efficient presentation of metabolite antigens. Proc Natl Acad Sci U S A 2020; 117:24974-24985. [PMID: 32958637 PMCID: PMC7547156 DOI: 10.1073/pnas.2011260117] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The antigen-presenting molecule MR1 (MHC class I-related protein 1) presents metabolite antigens derived from microbial vitamin B2 synthesis to activate mucosal-associated invariant T (MAIT) cells. Key aspects of this evolutionarily conserved pathway remain uncharacterized, including where MR1 acquires ligands and what accessory proteins assist ligand binding. We answer these questions by using a fluorophore-labeled stable MR1 antigen analog, a conformation-specific MR1 mAb, proteomic analysis, and a genome-wide CRISPR/Cas9 library screen. We show that the endoplasmic reticulum (ER) contains a pool of two unliganded MR1 conformers stabilized via interactions with chaperones tapasin and tapasin-related protein. This pool is the primary source of MR1 molecules for the presentation of exogenous metabolite antigens to MAIT cells. Deletion of these chaperones reduces the ER-resident MR1 pool and hampers antigen presentation and MAIT cell activation. The MR1 antigen-presentation pathway thus co-opts ER chaperones to fulfill its unique ability to present exogenous metabolite antigens captured within the ER.
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Affiliation(s)
- Hamish E G McWilliam
- Department of Microbiology and Immunology, The University of Melbourne, The Peter Doherty Institute for Infection and Immunity, Melbourne, VIC 3000, Australia;
- Department of Biochemistry and Molecular Biology, The University of Melbourne, Bio21 Molecular Science and Biotechnology Institute, Parkville, VIC 3010, Australia
| | - Jeffrey Y W Mak
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD 4072, Australia
- Australian Research Council Centre of Excellence in Advanced Molecular Imaging, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Wael Awad
- Infection and Immunity Program, Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Clayton, VIC 3800, Australia
- Australian Research Council Centre of Excellence in Advanced Molecular Imaging, Monash University, Clayton, VIC 3800, Australia
| | - Matthew Zorkau
- Department of Microbiology and Immunology, The University of Melbourne, The Peter Doherty Institute for Infection and Immunity, Melbourne, VIC 3000, Australia
| | - Sebastian Cruz-Gomez
- Department of Microbiology and Immunology, The University of Melbourne, The Peter Doherty Institute for Infection and Immunity, Melbourne, VIC 3000, Australia
| | - Hui Jing Lim
- Department of Microbiology and Immunology, The University of Melbourne, The Peter Doherty Institute for Infection and Immunity, Melbourne, VIC 3000, Australia
| | - Yuting Yan
- Department of Microbiology and Immunology, The University of Melbourne, The Peter Doherty Institute for Infection and Immunity, Melbourne, VIC 3000, Australia
| | - Sam Wormald
- Division of Systems Biology and Personalised Medicine, The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC 3052, Australia
- Department of Medical Biology, University of Melbourne, Parkville, VIC 3010, Australia
| | - Laura F Dagley
- Division of Systems Biology and Personalised Medicine, The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC 3052, Australia
- Department of Medical Biology, University of Melbourne, Parkville, VIC 3010, Australia
| | - Sidonia B G Eckle
- Department of Microbiology and Immunology, The University of Melbourne, The Peter Doherty Institute for Infection and Immunity, Melbourne, VIC 3000, Australia
| | - Alexandra J Corbett
- Department of Microbiology and Immunology, The University of Melbourne, The Peter Doherty Institute for Infection and Immunity, Melbourne, VIC 3000, Australia
| | - Haiyin Liu
- Department of Biochemistry and Molecular Biology, The University of Melbourne, Bio21 Molecular Science and Biotechnology Institute, Parkville, VIC 3010, Australia
| | - Shihan Li
- Department of Microbiology and Immunology, The University of Melbourne, The Peter Doherty Institute for Infection and Immunity, Melbourne, VIC 3000, Australia
- Australian Research Council Centre of Excellence in Advanced Molecular Imaging, University of Melbourne, Parkville, VIC 3010, Australia
| | - Scott J J Reddiex
- Department of Microbiology and Immunology, The University of Melbourne, The Peter Doherty Institute for Infection and Immunity, Melbourne, VIC 3000, Australia
- Australian Research Council Centre of Excellence in Advanced Molecular Imaging, University of Melbourne, Parkville, VIC 3010, Australia
- Murdoch Children's Research Institute, Royal Children's Hospital, Parkville, VIC 3052, Australia
| | - Justine D Mintern
- Department of Biochemistry and Molecular Biology, The University of Melbourne, Bio21 Molecular Science and Biotechnology Institute, Parkville, VIC 3010, Australia
| | - Ligong Liu
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD 4072, Australia
- Australian Research Council Centre of Excellence in Advanced Molecular Imaging, The University of Queensland, Brisbane, QLD 4072, Australia
| | - James McCluskey
- Department of Microbiology and Immunology, The University of Melbourne, The Peter Doherty Institute for Infection and Immunity, Melbourne, VIC 3000, Australia
| | - Jamie Rossjohn
- Infection and Immunity Program, Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Clayton, VIC 3800, Australia
- Australian Research Council Centre of Excellence in Advanced Molecular Imaging, Monash University, Clayton, VIC 3800, Australia
- Institute of Infection and Immunity, Cardiff University School of Medicine, Heath Park, CF14 4XN Cardiff, United Kingdom
| | - David P Fairlie
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD 4072, Australia;
- Australian Research Council Centre of Excellence in Advanced Molecular Imaging, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Jose A Villadangos
- Department of Microbiology and Immunology, The University of Melbourne, The Peter Doherty Institute for Infection and Immunity, Melbourne, VIC 3000, Australia;
- Department of Biochemistry and Molecular Biology, The University of Melbourne, Bio21 Molecular Science and Biotechnology Institute, Parkville, VIC 3010, Australia
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17
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Ilca FT, Drexhage LZ, Brewin G, Peacock S, Boyle LH. Distinct Polymorphisms in HLA Class I Molecules Govern Their Susceptibility to Peptide Editing by TAPBPR. Cell Rep 2020; 29:1621-1632.e3. [PMID: 31693900 PMCID: PMC7057265 DOI: 10.1016/j.celrep.2019.09.074] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Revised: 07/28/2019] [Accepted: 09/25/2019] [Indexed: 12/20/2022] Open
Abstract
Understanding how peptide selection is controlled on different major histocompatibility complex class I (MHC I) molecules is pivotal for determining how variations in these proteins influence our predisposition to infectious diseases, cancer, and autoinflammatory conditions. Although the intracellular chaperone TAPBPR edits MHC I peptides, it is unclear which allotypes are subjected to TAPBPR-mediated peptide editing. Here, we examine the ability of 97 different human leukocyte antigen (HLA) class I allotypes to interact with TAPBPR. We reveal a striking preference of TAPBPR for HLA-A, particularly for supertypes A2 and A24, over HLA-B and -C molecules. We demonstrate that the increased propensity of these HLA-A molecules to undergo TAPBPR-mediated peptide editing is determined by molecular features of the HLA-A F pocket, specifically residues H114 and Y116. This work reveals that specific polymorphisms in MHC I strongly influence their susceptibility to chaperone-mediated peptide editing, which may play a significant role in disease predisposition.
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Affiliation(s)
- F Tudor Ilca
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK
| | - Linnea Z Drexhage
- Faculty of Biology, University of Freiburg, Schaenzlestrasse 1, 79104 Freiburg, Germany
| | - Gemma Brewin
- Tissue Typing Laboratory, Box 209, Level 6 ATC, Cambridge University Hospitals, NHS Foundation Trust, Cambridge Biomedical Campus, Hills Road, Cambridge CB2 0QQ, UK
| | - Sarah Peacock
- Tissue Typing Laboratory, Box 209, Level 6 ATC, Cambridge University Hospitals, NHS Foundation Trust, Cambridge Biomedical Campus, Hills Road, Cambridge CB2 0QQ, UK
| | - Louise H Boyle
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK.
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18
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Ilca T, Boyle LH. The Ins and Outs of TAPBPR. Curr Opin Immunol 2020; 64:146-151. [PMID: 32814254 DOI: 10.1016/j.coi.2020.06.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2019] [Accepted: 06/25/2020] [Indexed: 11/26/2022]
Abstract
Peptide presentation on MHC class I molecules (MHC-I) is central to mounting effective antiviral and antitumoral immune responses. The tapasin-related protein TAPBPR is an MHC-I peptide editor which shapes the final peptide repertoire displayed on the cell surface. Here, we review recent findings which further elucidate the mechanisms by which TAPBPR performs peptide editing on a molecular level, and how glycosylation on MHC-I influences the interaction with TAPBPR and the peptide loading complex. We also explore how the function of TAPBPR can be utilized to promote exogenous peptide loading directly onto plasma-membrane expressed MHC-I. This has led to the development of new assays to investigate TAPBPR-mediated peptide editing and uncovered translational opportunities of utilizing TAPBPR to treat human disease.
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Affiliation(s)
- Tudor Ilca
- Department of Pathology, University of Cambridge, UK
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19
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Margulies DH, Jiang J, Natarajan K. Structural and dynamic studies of TAPBPR and Tapasin reveal the mechanism of peptide loading of MHC-I molecules. Curr Opin Immunol 2020; 64:71-79. [DOI: 10.1016/j.coi.2020.04.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Revised: 03/24/2020] [Accepted: 04/03/2020] [Indexed: 12/17/2022]
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20
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Sagert L, Hennig F, Thomas C, Tampé R. A loop structure allows TAPBPR to exert its dual function as MHC I chaperone and peptide editor. eLife 2020; 9:55326. [PMID: 32167472 PMCID: PMC7117912 DOI: 10.7554/elife.55326] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2020] [Accepted: 03/12/2020] [Indexed: 01/18/2023] Open
Abstract
Adaptive immunity vitally depends on major histocompatibility complex class I (MHC I) molecules loaded with peptides. Selective loading of peptides onto MHC I, referred to as peptide editing, is catalyzed by tapasin and the tapasin-related TAPBPR. An important catalytic role has been ascribed to a structural feature in TAPBPR called the scoop loop, but the exact function of the scoop loop remains elusive. Here, using a reconstituted system of defined peptide-exchange components including human TAPBPR variants, we uncover a substantial contribution of the scoop loop to the stability of the MHC I-chaperone complex and to peptide editing. We reveal that the scoop loop of TAPBPR functions as an internal peptide surrogate in peptide-depleted environments stabilizing empty MHC I and impeding peptide rebinding. The scoop loop thereby acts as an additional selectivity filter in shaping the repertoire of presented peptide epitopes and the formation of a hierarchical immune response.
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Affiliation(s)
- Lina Sagert
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Frankfurt, Germany
| | - Felix Hennig
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Frankfurt, Germany
| | - Christoph Thomas
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Frankfurt, Germany
| | - Robert Tampé
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Frankfurt, Germany
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21
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Trowitzsch S, Tampé R. Multifunctional Chaperone and Quality Control Complexes in Adaptive Immunity. Annu Rev Biophys 2020; 49:135-161. [PMID: 32004089 DOI: 10.1146/annurev-biophys-121219-081643] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The fundamental process of adaptive immunity relies on the differentiation of self from nonself. Nucleated cells are continuously monitored by effector cells of the immune system, which police the peptide status presented via cell surface molecules. Recent integrative structural approaches have provided insights toward our understanding of how sophisticated cellular machineries shape such hierarchical immune surveillance. Biophysical and structural achievements were invaluable for defining the interconnection of many key factors during antigen processing and presentation, and helped to solve several conundrums that persisted for many years. In this review, we illuminate the numerous quality control machineries involved in different steps during the maturation of major histocompatibility complex class I (MHC I) proteins, from their synthesis in the endoplasmic reticulum to folding and trafficking via the secretory pathway, optimization of antigenic cargo, final release to the cell surface, and engagement with their cognate receptors on cytotoxic T lymphocytes.
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Affiliation(s)
- Simon Trowitzsch
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, 60438 Frankfurt am Main, Germany; ,
| | - Robert Tampé
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, 60438 Frankfurt am Main, Germany; ,
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22
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Praest P, Liaci AM, Förster F, Wiertz EJ. New insights into the structure of the MHC class I peptide-loading complex and mechanisms of TAP inhibition by viral immune evasion proteins. Mol Immunol 2019; 113:103-114. [DOI: 10.1016/j.molimm.2018.03.020] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2017] [Revised: 03/16/2018] [Accepted: 03/22/2018] [Indexed: 01/08/2023]
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23
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Natarajan K, Jiang J, Margulies DH. Structural aspects of chaperone-mediated peptide loading in the MHC-I antigen presentation pathway. Crit Rev Biochem Mol Biol 2019; 54:164-173. [PMID: 31084439 DOI: 10.1080/10409238.2019.1610352] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Recognition of foreign and dysregulated antigens by the cellular innate and adaptive immune systems is in large part dependent on the cell surface display of peptide/MHC (pMHC) complexes. The formation of such complexes requires the generation of antigenic peptides, proper folding of MHC molecules, loading of peptides onto MHC molecules, glycosylation, and transport to the plasma membrane. This complex series of biosynthetic, biochemical, and cell biological reactions is known as "antigen processing and presentation". Here, we summarize recent work, focused on the structural and functional characterization of the key MHC-I-dedicated chaperones, tapasin, and TAPBPR. The mechanisms reflect the ability of conformationally flexible molecules to adapt to their ligands, and are comparable to similar processes that are exploited in peptide antigen loading in the MHC-II pathway.
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Affiliation(s)
- Kannan Natarajan
- a Molecular Biology Section, Laboratory of Immune System Biology , National Institute of Allergy and Infectious Diseases, National Institutes of Health , Bethesda , MD , USA
| | - Jiansheng Jiang
- a Molecular Biology Section, Laboratory of Immune System Biology , National Institute of Allergy and Infectious Diseases, National Institutes of Health , Bethesda , MD , USA
| | - David H Margulies
- a Molecular Biology Section, Laboratory of Immune System Biology , National Institute of Allergy and Infectious Diseases, National Institutes of Health , Bethesda , MD , USA
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24
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Jiang J, Natarajan K, Margulies DH. MHC Molecules, T cell Receptors, Natural Killer Cell Receptors, and Viral Immunoevasins-Key Elements of Adaptive and Innate Immunity. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1172:21-62. [PMID: 31628650 DOI: 10.1007/978-981-13-9367-9_2] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Molecules encoded by the Major Histocompatibility Complex (MHC) bind self or foreign peptides and display these at the cell surface for recognition by receptors on T lymphocytes (designated T cell receptors-TCR) or on natural killer (NK) cells. These ligand/receptor interactions govern T cell and NK cell development as well as activation of T memory and effector cells. Such cells participate in immunological processes that regulate immunity to various pathogens, resistance and susceptibility to cancer, and autoimmunity. The past few decades have witnessed the accumulation of a huge knowledge base of the molecular structures of MHC molecules bound to numerous peptides, of TCRs with specificity for many different peptide/MHC (pMHC) complexes, of NK cell receptors (NKR), of MHC-like viral immunoevasins, and of pMHC/TCR and pMHC/NKR complexes. This chapter reviews the structural principles that govern peptide/MHC (pMHC), pMHC/TCR, and pMHC/NKR interactions, for both MHC class I (MHC-I) and MHC class II (MHC-II) molecules. In addition, we discuss the structures of several representative MHC-like molecules. These include host molecules that have distinct biological functions, as well as virus-encoded molecules that contribute to the evasion of the immune response.
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Affiliation(s)
- Jiansheng Jiang
- Molecular Biology Section, Laboratory of Immune System Biology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bldg. 10, Room 11D07, 10 Center Drive, Bethesda, MD, 20892-1892, USA.
| | - Kannan Natarajan
- Molecular Biology Section, Laboratory of Immune System Biology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bldg. 10, Room 11D07, 10 Center Drive, Bethesda, MD, 20892-1892, USA
| | - David H Margulies
- Molecular Biology Section, Laboratory of Immune System Biology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bldg. 10, Room 11D12, 10 Center Drive, Bethesda, MD, 20892-1892, USA
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25
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Abstract
Major histocompatibility class I (MHC-I) molecules bind peptides derived from cellular synthesis and display them at the cell surface for recognition by receptors on T lymphocytes (TCR) or natural killer (NK) cells. Such recognition provides a crucial step in autoimmunity, identification of bacterial and viral pathogens, and anti-tumor responses. Understanding the mechanism by which such antigenic peptides in the ER are loaded and exchanged for higher affinity peptides onto MHC molecules has recently been clarified by cryo-EM and X-ray studies of the multimolecular peptide loading complex (PLC) and a unimolecular tapasin-like chaperone designated TAPBPR. Insights from these structural studies and complementary solution NMR experiments provide a basis for understanding mechanisms related to immune antigen presentation.
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26
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Ilca FT, Neerincx A, Hermann C, Marcu A, Stevanović S, Deane JE, Boyle LH. TAPBPR mediates peptide dissociation from MHC class I using a leucine lever. eLife 2018; 7:40126. [PMID: 30484775 PMCID: PMC6307860 DOI: 10.7554/elife.40126] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2018] [Accepted: 11/28/2018] [Indexed: 11/29/2022] Open
Abstract
Tapasin and TAPBPR are known to perform peptide editing on major histocompatibility complex class I (MHC I) molecules; however, the precise molecular mechanism(s) involved in this process remain largely enigmatic. Here, using immunopeptidomics in combination with novel cell-based assays that assess TAPBPR-mediated peptide exchange, we reveal a critical role for the K22-D35 loop of TAPBPR in mediating peptide exchange on MHC I. We identify a specific leucine within this loop that enables TAPBPR to facilitate peptide dissociation from MHC I. Moreover, we delineate the molecular features of the MHC I F pocket required for TAPBPR to promote peptide dissociation in a loop-dependent manner. These data reveal that chaperone-mediated peptide editing on MHC I can occur by different mechanisms dependent on the C-terminal residue that the MHC I accommodates in its F pocket and provide novel insights that may inform the therapeutic potential of TAPBPR manipulation to increase tumour immunogenicity.
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Affiliation(s)
- F Tudor Ilca
- Department of Pathology, University of Cambridge, Cambridge, United Kingdom
| | - Andreas Neerincx
- Department of Pathology, University of Cambridge, Cambridge, United Kingdom
| | - Clemens Hermann
- Department of Integrative Biomedical Sciences, Division of Chemical and Systems Biology, Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town, South Africa
| | - Ana Marcu
- Department of Immunology, Interfaculty Institute for Cell Biology, University of Tübingen, Tübingen, Germany
| | - Stefan Stevanović
- Department of Immunology, Interfaculty Institute for Cell Biology, University of Tübingen, Tübingen, Germany.,DKFZ Partner Site Tübingen, German Cancer Consortium, Tübingen, Germany
| | - Janet E Deane
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge, United Kingdom
| | - Louise H Boyle
- Department of Pathology, University of Cambridge, Cambridge, United Kingdom
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27
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Ilca FT, Neerincx A, Wills MR, de la Roche M, Boyle LH. Utilizing TAPBPR to promote exogenous peptide loading onto cell surface MHC I molecules. Proc Natl Acad Sci U S A 2018; 115:E9353-E9361. [PMID: 30213851 PMCID: PMC6176578 DOI: 10.1073/pnas.1809465115] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The repertoire of peptides displayed at the cell surface by MHC I molecules is shaped by two intracellular peptide editors, tapasin and TAPBPR. While cell-free assays have proven extremely useful in identifying the function of both of these proteins, here we explored whether a more physiological system could be developed to assess TAPBPR-mediated peptide editing on MHC I. We reveal that membrane-associated TAPBPR targeted to the plasma membrane retains its ability to function as a peptide editor and efficiently catalyzes peptide exchange on surface-expressed MHC I molecules. Additionally, we show that soluble TAPBPR, consisting of the luminal domain alone, added to intact cells, also functions as an effective peptide editor on surface MHC I molecules. Thus, we have established two systems in which TAPBPR-mediated peptide exchange on MHC class I can be interrogated. Furthermore, we could use both plasma membrane-targeted and exogenous soluble TAPBPR to display immunogenic peptides on surface MHC I molecules and consequently induce T cell receptor engagement, IFN-γ secretion, and T cell-mediated killing of target cells. Thus, we have developed an efficient way to by-pass the natural antigen presentation pathway of cells and load immunogenic peptides of choice onto cells. Our findings highlight a potential therapeutic use for TAPBPR in increasing the immunogenicity of tumors in the future.
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Affiliation(s)
- F Tudor Ilca
- Department of Pathology, University of Cambridge, CB2 1QP Cambridge, United Kingdom
| | - Andreas Neerincx
- Department of Pathology, University of Cambridge, CB2 1QP Cambridge, United Kingdom
| | - Mark R Wills
- Department of Medicine, University of Cambridge, Addenbrookes Hospital, CB2 0QQ Cambridge, United Kingdom
| | - Maike de la Roche
- Cancer Research UK Cambridge Institute, University of Cambridge, Li Ka Shing Centre, CB2 0RE Cambridge, United Kingdom
| | - Louise H Boyle
- Department of Pathology, University of Cambridge, CB2 1QP Cambridge, United Kingdom;
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28
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Trowitzsch S, Tampé R. ABC Transporters in Dynamic Macromolecular Assemblies. J Mol Biol 2018; 430:4481-4495. [DOI: 10.1016/j.jmb.2018.07.028] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2018] [Revised: 07/24/2018] [Accepted: 07/30/2018] [Indexed: 12/28/2022]
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29
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Vigneron N, Ferrari V, Van den Eynde BJ, Cresswell P, Leonhardt RM. Cytosolic Processing Governs TAP-Independent Presentation of a Critical Melanoma Antigen. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2018; 201:1875-1888. [PMID: 30135181 PMCID: PMC6457910 DOI: 10.4049/jimmunol.1701479] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2017] [Accepted: 07/26/2018] [Indexed: 12/30/2022]
Abstract
Cancer immunotherapy has been flourishing in recent years with remarkable clinical success. But as more patients are treated, a shadow is emerging that has haunted other cancer therapies: tumors develop resistance. Resistance is often caused by defects in the MHC class I Ag presentation pathway critical for CD8 T cell-mediated tumor clearance. TAP and tapasin, both key players in the pathway, are frequently downregulated in human cancers, correlating with poor patient survival. Reduced dependence on these factors may promote vaccine efficiency by limiting immune evasion. In this study, we demonstrate that PMEL209-217, a promising phase 3 trial-tested antimelanoma vaccine candidate, is robustly presented by various TAP- and/or tapasin-deficient cell lines. This striking characteristic may underlie its potency as a vaccine. Surprisingly, cytosolic proteasomes generate the peptide even for TAP-independent presentation, whereas tripeptidyl peptidase 2 (TPP2) efficiently degrades the epitope. Consequently, inhibiting TPP2 substantially boosts PMEL209-217 presentation, suggesting a possible strategy to improve the therapeutic efficacy of the vaccine.
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Affiliation(s)
- Nathalie Vigneron
- Ludwig Institute for Cancer Research, Brussels B-1200, Belgium
- de Duve Institute, University of Louvain, Brussels B-1200, Belgium
- Walloon Excellence in Life Sciences and Biotechnology, Brussels B-1200, Belgium
| | - Violette Ferrari
- Ludwig Institute for Cancer Research, Brussels B-1200, Belgium
- de Duve Institute, University of Louvain, Brussels B-1200, Belgium
- Walloon Excellence in Life Sciences and Biotechnology, Brussels B-1200, Belgium
| | - Benoît J Van den Eynde
- Ludwig Institute for Cancer Research, Brussels B-1200, Belgium;
- de Duve Institute, University of Louvain, Brussels B-1200, Belgium
- Walloon Excellence in Life Sciences and Biotechnology, Brussels B-1200, Belgium
| | - Peter Cresswell
- Department of Immunobiology, Yale University, New Haven, CT 06519; and
- Department of Cell Biology, Yale University, New Haven, CT 06519
| | - Ralf M Leonhardt
- Department of Immunobiology, Yale University, New Haven, CT 06519; and
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30
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Neerincx A, Boyle LH. Preferential interaction of MHC class I with TAPBPR in the absence of glycosylation. Mol Immunol 2018; 113:58-66. [PMID: 30077416 PMCID: PMC6859791 DOI: 10.1016/j.molimm.2018.06.269] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2017] [Revised: 04/23/2018] [Accepted: 06/14/2018] [Indexed: 11/17/2022]
Abstract
We recently discovered that TAPBPR promotes reglucosylation of the N-linked glycan on MHC class I molecules, a modification that restores their recognition by calreticulin and reincorporation into the peptide-loading complex. We wondered whether TAPBPR displayed some degree of glycan specificity, as is known to be the case for tapasin via its interaction with calreticulin & ERp57, or whether its interaction with MHC class I was glycan independent. Here, we explored this by comparing the ability of TAPBPR to bind to MHC class I containing either an intact or disrupted NxS/T glycosylation consensus sequence. In contrast to tapasin, TAPBPR bound strongly to MHC class I molecules that lacked N-linked glycosylation, suggesting that the TAPBPR:MHC class I interaction is glycan independent. Furthermore, we found that glycosylated HLA-A2 preferentially interacts with tapasin rather than TAPBPR, possibly explaining, in part, why MHC class I molecules bind efficiently to tapasin in the face of an alternative chaperone. The distinction in glycan specificity between the two peptide editors suggests that TAPBPR may bind to MHC class I molecules that are associated with a broader diversity of oligosaccharides attached compared with tapasin. This may explain, to some extent, the ability of TAPBPR to interact with MHC class I molecules outside of the ER.
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Affiliation(s)
- Andreas Neerincx
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, UK
| | - Louise H Boyle
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, UK.
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31
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McShan AC, Natarajan K, Kumirov VK, Flores-Solis D, Jiang J, Badstübner M, Toor JS, Bagshaw CR, Kovrigin EL, Margulies DH, Sgourakis NG. Peptide exchange on MHC-I by TAPBPR is driven by a negative allostery release cycle. Nat Chem Biol 2018; 14:811-820. [PMID: 29988068 PMCID: PMC6202177 DOI: 10.1038/s41589-018-0096-2] [Citation(s) in RCA: 65] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2017] [Revised: 05/02/2018] [Accepted: 05/21/2018] [Indexed: 01/09/2023]
Abstract
Chaperones TAPBPR and tapasin associate with class-I major histocompatibility complexes (MHC-I) to promote optimization (editing) of peptide cargo. Here, we use solution NMR to investigate the mechanism of peptide exchange. We identify TAPBPR-induced conformational changes on conserved MHC-I molecular surfaces, consistent with our independently determined X-ray structure of the complex. Dynamics present in the empty MHC-I are stabilized by TAPBPR, and become progressively dampened with increasing peptide occupancy. Incoming peptides are recognized according to the global stability of the final pMHC-I product, and anneal in a native-like conformation to be edited by TAPBPR. Our results demonstrate an inverse relationship between MHC-I peptide occupancy and TAPBPR binding affinity, where the lifetime and structural features of transiently bound peptides controls the regulation of a conformational switch, located near the TAPBPR binding site, which triggers TAPBPR release. These results suggest a similar mechanism for the function of tapasin in the peptide-loading complex.
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Affiliation(s)
- Andrew C McShan
- Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, CA, USA
| | - Kannan Natarajan
- Molecular Biology Section, Laboratory of Immune System Biology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MA, USA
| | - Vlad K Kumirov
- Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, CA, USA
| | - David Flores-Solis
- Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, CA, USA
| | - Jiansheng Jiang
- Molecular Biology Section, Laboratory of Immune System Biology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MA, USA
| | - Mareike Badstübner
- Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, CA, USA
| | - Jugmohit S Toor
- Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, CA, USA
| | - Clive R Bagshaw
- Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, CA, USA
| | | | - David H Margulies
- Molecular Biology Section, Laboratory of Immune System Biology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MA, USA
| | - Nikolaos G Sgourakis
- Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, CA, USA.
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32
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Jiang J, Natarajan K, Boyd LF, Morozov GI, Mage MG, Margulies DH. Crystal structure of a TAPBPR-MHC I complex reveals the mechanism of peptide editing in antigen presentation. Science 2017; 358:1064-1068. [PMID: 29025991 PMCID: PMC6320693 DOI: 10.1126/science.aao5154] [Citation(s) in RCA: 86] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2017] [Accepted: 10/04/2017] [Indexed: 12/15/2022]
Abstract
Central to CD8+ T cell-mediated immunity is the recognition of peptide-major histocompatibility complex class I (p-MHC I) proteins displayed by antigen-presenting cells. Chaperone-mediated loading of high-affinity peptides onto MHC I is a key step in the MHC I antigen presentation pathway. However, the structure of MHC I with a chaperone that facilitates peptide loading has not been determined. We report the crystal structure of MHC I in complex with the peptide editor TAPBPR (TAP-binding protein-related), a tapasin homolog. TAPBPR remodels the peptide-binding groove of MHC I, resulting in the release of low-affinity peptide. Changes include groove relaxation, modifications of key binding pockets, and domain adjustments. This structure captures a peptide-receptive state of MHC I and provides insights into the mechanism of peptide editing by TAPBPR and, by analogy, tapasin.
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Affiliation(s)
- Jiansheng Jiang
- Molecular Biology Section, Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA
| | - Kannan Natarajan
- Molecular Biology Section, Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA
| | - Lisa F Boyd
- Molecular Biology Section, Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA
| | - Giora I Morozov
- Molecular Biology Section, Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA
- Hebrew University of Jerusalem, Robert H. Smith Faculty of Agriculture, Food and Environment, Rehovot 76100, Israel
| | - Michael G Mage
- Molecular Biology Section, Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA
| | - David H Margulies
- Molecular Biology Section, Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
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33
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Thomas C, Tampé R. Structure of the TAPBPR–MHC I complex defines the mechanism of peptide loading and editing. Science 2017; 358:1060-1064. [DOI: 10.1126/science.aao6001] [Citation(s) in RCA: 93] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Accepted: 09/20/2017] [Indexed: 12/22/2022]
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34
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Grotzke JE, Sengupta D, Lu Q, Cresswell P. The ongoing saga of the mechanism(s) of MHC class I-restricted cross-presentation. Curr Opin Immunol 2017; 46:89-96. [PMID: 28528219 PMCID: PMC5554740 DOI: 10.1016/j.coi.2017.03.015] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2017] [Accepted: 03/23/2017] [Indexed: 11/21/2022]
Abstract
Cross-presentation is an MHC-I antigen processing pathway that results in the presentation of peptides from exogenous viral, bacterial, parasitic, and tumor antigens and ultimately leads to priming of naïve CD8+ T cells. This process involves several cellular compartments and multiple components. Successful generation of MHC-I-peptide complexes requires that these components act together in a coordinated fashion. We discuss recent findings on the source of MHC-I, the role of the TAP transporter, the importance of intracellular trafficking events, mechanisms of antigen access the cytosol, and how innate immune signals can affect presentation, with an emphasis on how these pathways compare to conventional antigen presentation and how they correlate with existing data.
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Affiliation(s)
- Jeff E Grotzke
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT 06520-8011, United States
| | - Debrup Sengupta
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT 06520-8011, United States
| | - Qiao Lu
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT 06520-8011, United States
| | - Peter Cresswell
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT 06520-8011, United States; Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520-8011, United States.
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35
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Neerincx A, Boyle LH. Properties of the tapasin homologue TAPBPR. Curr Opin Immunol 2017; 46:97-102. [PMID: 28528220 DOI: 10.1016/j.coi.2017.04.008] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2016] [Revised: 04/01/2017] [Accepted: 04/17/2017] [Indexed: 11/17/2022]
Abstract
The presentation of antigenic peptides by MHC class I molecules plays a vital role in generating T cell responses against infection and cancer. Over the last two decades the central role of tapasin as a peptide editor that influences the loading and optimisation of peptides onto MHC class I molecules has been extensively characterised. Recently, it has become evident that the tapasin-related protein, TAPBPR, functions as a second peptide editor which influences the peptides displayed by MHC class I molecules. Here, we review the discovery of TAPBPR and current understanding of this novel protein in relation to its closest homologue tapasin.
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Affiliation(s)
- Andreas Neerincx
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK
| | - Louise H Boyle
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK.
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36
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Neerincx A, Hermann C, Antrobus R, van Hateren A, Cao H, Trautwein N, Stevanović S, Elliott T, Deane JE, Boyle LH. TAPBPR bridges UDP-glucose:glycoprotein glucosyltransferase 1 onto MHC class I to provide quality control in the antigen presentation pathway. eLife 2017; 6:e23049. [PMID: 28425917 PMCID: PMC5441866 DOI: 10.7554/elife.23049] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Accepted: 04/14/2017] [Indexed: 11/24/2022] Open
Abstract
Recently, we revealed that TAPBPR is a peptide exchange catalyst that is important for optimal peptide selection by MHC class I molecules. Here, we asked whether any other co-factors associate with TAPBPR, which would explain its effect on peptide selection. We identify an interaction between TAPBPR and UDP-glucose:glycoprotein glucosyltransferase 1 (UGT1), a folding sensor in the calnexin/calreticulin quality control cycle that is known to regenerate the Glc1Man9GlcNAc2 moiety on glycoproteins. Our results suggest the formation of a multimeric complex, dependent on a conserved cysteine at position 94 in TAPBPR, in which TAPBPR promotes the association of UGT1 with peptide-receptive MHC class I molecules. We reveal that the interaction between TAPBPR and UGT1 facilities the reglucosylation of the glycan on MHC class I molecules, promoting their recognition by calreticulin. Our results suggest that in addition to being a peptide editor, TAPBPR improves peptide optimisation by promoting peptide-receptive MHC class I molecules to associate with the peptide-loading complex.
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Affiliation(s)
- Andreas Neerincx
- Department of Pathology, University of Cambridge, Cambridge, United Kingdom
| | - Clemens Hermann
- Department of Pathology, University of Cambridge, Cambridge, United Kingdom
| | - Robin Antrobus
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge, United Kingdom
| | - Andy van Hateren
- Faculty of Medicine, University of Southampton, Southampton, United Kingdom
- Institute for Life Science, University of Southampton, Southampton, United Kingdom
| | - Huan Cao
- Division of Applied Medicine, Institute of Medical Sciences, University of Aberdeen, Aberdeen, United Kingdom
| | - Nico Trautwein
- Department of Immunology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Stefan Stevanović
- Department of Immunology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Tim Elliott
- Faculty of Medicine, University of Southampton, Southampton, United Kingdom
- Institute for Life Science, University of Southampton, Southampton, United Kingdom
| | - Janet E Deane
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge, United Kingdom
| | - Louise H Boyle
- Department of Pathology, University of Cambridge, Cambridge, United Kingdom
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37
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van Hateren A, Bailey A, Elliott T. Recent advances in Major Histocompatibility Complex (MHC) class I antigen presentation: Plastic MHC molecules and TAPBPR-mediated quality control. F1000Res 2017; 6:158. [PMID: 28299193 PMCID: PMC5321123 DOI: 10.12688/f1000research.10474.1] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 02/13/2017] [Indexed: 01/25/2023] Open
Abstract
We have known since the late 1980s that the function of classical major histocompatibility complex (MHC) class I molecules is to bind peptides and display them at the cell surface to cytotoxic T cells. Recognition by these sentinels of the immune system can lead to the destruction of the presenting cell, thus protecting the host from pathogens and cancer. Classical MHC class I molecules (MHC I hereafter) are co-dominantly expressed, polygenic, and exceptionally polymorphic and have significant sequence diversity. Thus, in most species, there are many different MHC I allotypes expressed, each with different peptide-binding specificity, which can have a dramatic effect on disease outcome. Although MHC allotypes vary in their primary sequence, they share common tertiary and quaternary structures. Here, we review the evidence that, despite this commonality, polymorphic amino acid differences between allotypes alter the ability of MHC I molecules to change shape (that is, their conformational plasticity). We discuss how the peptide loading co-factor tapasin might modify this plasticity to augment peptide loading. Lastly, we consider recent findings concerning the functions of the non-classical MHC I molecule HLA-E as well as the tapasin-related protein TAPBPR (transporter associated with antigen presentation binding protein-related), which has been shown to act as a second quality-control stage in MHC I antigen presentation.
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Affiliation(s)
- Andy van Hateren
- Institute for Life Sciences and Cancer Sciences Unit, University of Southampton, Southampton, UK
| | - Alistair Bailey
- Institute for Life Sciences and Cancer Sciences Unit, University of Southampton, Southampton, UK
| | - Tim Elliott
- Institute for Life Sciences and Cancer Sciences Unit, University of Southampton, Southampton, UK
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38
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Thomas C, Tampé R. Proofreading of Peptide-MHC Complexes through Dynamic Multivalent Interactions. Front Immunol 2017; 8:65. [PMID: 28228754 PMCID: PMC5296336 DOI: 10.3389/fimmu.2017.00065] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2016] [Accepted: 01/16/2017] [Indexed: 11/18/2022] Open
Abstract
The adaptive immune system is able to detect and destroy cells that are malignantly transformed or infected by intracellular pathogens. Specific immune responses against these cells are elicited by antigenic peptides that are presented on major histocompatibility complex class I (MHC I) molecules and recognized by cytotoxic T lymphocytes at the cell surface. Since these MHC I-presented peptides are generated in the cytosol by proteasomal protein degradation, they can be metaphorically described as a window providing immune cells with insights into the state of the cellular proteome. A crucial element of MHC I antigen presentation is the peptide-loading complex (PLC), a multisubunit machinery, which contains as key constituents the transporter associated with antigen processing (TAP) and the MHC I-specific chaperone tapasin (Tsn). While TAP recognizes and shuttles the cytosolic antigenic peptides into the endoplasmic reticulum (ER), Tsn samples peptides in the ER for their ability to form stable complexes with MHC I, a process called peptide proofreading or peptide editing. Through its selection of peptides that improve MHC I stability, Tsn contributes to the hierarchy of immunodominant peptide epitopes. Despite the fact that it concerns a key event in adaptive immunity, insights into the catalytic mechanism of peptide proofreading carried out by Tsn have only lately been gained via biochemical, biophysical, and structural studies. Furthermore, a Tsn homolog called TAP-binding protein-related (TAPBPR) has only recently been demonstrated to function as a second MHC I-specific chaperone and peptide proofreader. Although TAPBPR is PLC-independent and has a distinct allomorph specificity, it is likely to share a common catalytic mechanism with Tsn. This review focuses on the current knowledge of the multivalent protein–protein interactions and the concomitant dynamic molecular processes underlying peptide-proofreading catalysis. We do not only derive a model that highlights the common mechanistic principles shared by the MHC I editors Tsn and TAPBPR, and the MHC II editor HLA-DM, but also illustrate the distinct quality control strategies employed by these chaperones to sample epitopes. Unraveling the mechanistic underpinnings of catalyzed peptide proofreading will be crucial for a thorough understanding of many aspects of immune recognition, from infection control and tumor immunity to autoimmune diseases and transplant rejection.
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Affiliation(s)
- Christoph Thomas
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt , Frankfurt am Main , Germany
| | - Robert Tampé
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt , Frankfurt am Main , Germany
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39
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Interaction of TAPBPR, a tapasin homolog, with MHC-I molecules promotes peptide editing. Proc Natl Acad Sci U S A 2016; 113:E1006-15. [PMID: 26869717 DOI: 10.1073/pnas.1519894113] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Peptide loading of major histocompatibility complex class I (MHC-I) molecules is central to antigen presentation, self-tolerance, and CD8(+) T-cell activation. TAP binding protein, related (TAPBPR), a widely expressed tapasin homolog, is not part of the classical MHC-I peptide-loading complex (PLC). Using recombinant MHC-I molecules, we show that TAPBPR binds HLA-A*02:01 and several other MHC-I molecules that are either peptide-free or loaded with low-affinity peptides. Fluorescence polarization experiments establish that TAPBPR augments peptide binding by MHC-I. The TAPBPR/MHC-I interaction is reversed by specific peptides, related to their affinity. Mutational and small-angle X-ray scattering (SAXS) studies confirm the structural similarities of TAPBPR with tapasin. These results support a role of TAPBPR in stabilizing peptide-receptive conformation(s) of MHC-I, permitting peptide editing.
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40
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Hermann C, Trowsdale J, Boyle LH. TAPBPR: a new player in the MHC class I presentation pathway. ACTA ACUST UNITED AC 2015; 85:155-66. [PMID: 25720504 DOI: 10.1111/tan.12538] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
In order to provide specificity for T cell responses against pathogens and tumours, major histocompatibility complex (MHC) class I molecules present high-affinity peptides at the cell surface to T cells. A key player for peptide loading is the MHC class I-dedicated chaperone tapasin. Recently we discovered a second MHC class I-dedicated chaperone, the tapasin-related protein TAPBPR. Here, we review the major steps in the MHC class I pathway and the TAPBPR data. We discuss the potential function of TAPBPR in the MHC class I pathway and the involvement of this previously uncharacterised protein in human health and disease.
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Affiliation(s)
- C Hermann
- Department of Pathology, University of Cambridge, Cambridge CB2 1QP, UK
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Hermann C, van Hateren A, Trautwein N, Neerincx A, Duriez PJ, Stevanović S, Trowsdale J, Deane JE, Elliott T, Boyle LH. TAPBPR alters MHC class I peptide presentation by functioning as a peptide exchange catalyst. eLife 2015; 4:e09617. [PMID: 26439010 PMCID: PMC4718805 DOI: 10.7554/elife.09617] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2015] [Accepted: 10/05/2015] [Indexed: 12/29/2022] Open
Abstract
Our understanding of the antigen presentation pathway has recently been enhanced with the identification that the tapasin-related protein TAPBPR is a second major histocompatibility complex (MHC) class I-specific chaperone. We sought to determine whether, like tapasin, TAPBPR can also influence MHC class I peptide selection by functioning as a peptide exchange catalyst. We show that TAPBPR can catalyse the dissociation of peptides from peptide-MHC I complexes, enhance the loading of peptide-receptive MHC I molecules, and discriminate between peptides based on affinity in vitro. In cells, the depletion of TAPBPR increased the diversity of peptides presented on MHC I molecules, suggesting that TAPBPR is involved in restricting peptide presentation. Our results suggest TAPBPR binds to MHC I in a peptide-receptive state and, like tapasin, works to enhance peptide optimisation. It is now clear there are two MHC class I specific peptide editors, tapasin and TAPBPR, intimately involved in controlling peptide presentation to the immune system.
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Affiliation(s)
- Clemens Hermann
- Department of Pathology, University of Cambridge, Cambridge, United Kingdom
| | - Andy van Hateren
- Faculty of Medicine and Institute for Life Science, University of Southampton, Southampton, United Kingdom
| | - Nico Trautwein
- Department of Immunology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Andreas Neerincx
- Department of Pathology, University of Cambridge, Cambridge, United Kingdom
| | - Patrick J Duriez
- Cancer Research UK Protein Core Facility, Faculty of Medicine, University of Southampton, Southampton, United Kingdom
| | - Stefan Stevanović
- Department of Immunology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - John Trowsdale
- Department of Pathology, University of Cambridge, Cambridge, United Kingdom
| | - Janet E Deane
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge, United Kingdom
| | - Tim Elliott
- Faculty of Medicine and Institute for Life Science, University of Southampton, Southampton, United Kingdom
| | - Louise H Boyle
- Department of Pathology, University of Cambridge, Cambridge, United Kingdom
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Oliveira CC, van Hall T. Alternative Antigen Processing for MHC Class I: Multiple Roads Lead to Rome. Front Immunol 2015; 6:298. [PMID: 26097483 PMCID: PMC4457021 DOI: 10.3389/fimmu.2015.00298] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Accepted: 05/22/2015] [Indexed: 12/31/2022] Open
Abstract
The well described conventional antigen-processing pathway is accountable for most peptides that end up in MHC class I molecules at the cell surface. These peptides experienced liberation by the proteasome and transport by the peptide transporter TAP. However, there are multiple roads that lead to Rome, illustrated by the increasing number of alternative processing pathways that have been reported during last years. Interestingly, TAP-deficient individuals do not succumb to viral infections, suggesting that CD8 T cell immunity is sufficiently supported by alternative TAP-independent processing pathways. To date, a diversity of viral and endogenous TAP-independent peptides have been identified in the grooves of different MHC class I alleles. Some of these peptides are not displayed by normal TAP-positive cells and we therefore called them TEIPP, for “T-cell epitopes associated with impaired peptide processing.” TEIPPs are hidden self-antigens, are derived from normal housekeeping proteins, and are processed via unconventional processing pathways. Per definition, TEIPPs are presented via TAP-independent pathways, but recent data suggest that part of this repertoire still depend on proteasome and metalloprotease activity. An exception is the C-terminal peptide of the endoplasmic reticulum (ER)-membrane-spanning ceramide synthase Trh4 that is surprisingly liberated by the signal peptide peptidase (SPP), the proteolytic enzyme involved in cleaving leader sequences. The intramembrane cleaving SPP is thereby an important contributor of TAP-independent peptides. Its family members, like the Alzheimer’s related presenilins, might contribute as well, according to our preliminary data. Finally, alternative peptide routing is an emerging field and includes processes like the unfolded protein response, the ER-associated degradation, and autophagy-associated vesicular pathways. These data convince us that there is a world to be discovered in the field of unconventional antigen processing.
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Affiliation(s)
- Cláudia C Oliveira
- Department of Clinical Oncology, Leiden University Medical Center , Leiden , Netherlands
| | - Thorbald van Hall
- Department of Clinical Oncology, Leiden University Medical Center , Leiden , Netherlands
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Porter KM, Hermann C, Traherne JA, Boyle LH. TAPBPR isoforms exhibit altered association with MHC class I. Immunology 2014; 142:289-99. [PMID: 24444341 PMCID: PMC4008236 DOI: 10.1111/imm.12253] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2013] [Revised: 01/14/2014] [Accepted: 01/14/2014] [Indexed: 01/14/2023] Open
Abstract
The tapasin-related protein TAPBPR is a novel component of the antigen processing and presentation pathway, which binds to MHC class I coupled with β2-microglobulin. We describe six alternatively spliced TAPBPR transcripts from the TAPBPL gene and investigate three of these at a protein level. TAPBPR transcripts lacking exon 5 result in loss of the membrane proximal IgC domain and loss of ability to bind to MHC class I. Alternative acceptor and donor splice sites in exon 4 of TAPBPR altered the reading frame in the IgV domain and produced a truncated TAPBPR product. An additional exon in the TAPBPL gene was identified that encodes extra residues in the cytoplasmic tail of TAPBPR. This longer TAPBPR protein interacted with MHC class I but was attenuated in its ability to down-regulate surface expression of MHC class I. The abundance of these alternative transcripts in peripheral blood mononuclear cells and dendritic cells suggests an important role of TAPBPR isoforms in vivo.
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Affiliation(s)
- Keith M Porter
- Department of Pathology, Cambridge Institute of Medical Research, University of Cambridge, Wellcome TrustCambridge, UK
| | - Clemens Hermann
- Department of Pathology, Cambridge Institute of Medical Research, University of Cambridge, Wellcome TrustCambridge, UK
| | - James A Traherne
- Department of Pathology, Cambridge Institute of Medical Research, University of Cambridge, Wellcome TrustCambridge, UK
| | - Louise H Boyle
- Department of Pathology, Cambridge Institute of Medical Research, University of Cambridge, Wellcome TrustCambridge, UK
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