{"id":{"repo_id":"cambridge","oai_identifier":"oai:www.repository.cam.ac.uk:1810/304579"},"canonical_url":"https://search.dev.ndltd.org/etd/cambridge/oai:www.repository.cam.ac.uk:1810/304579","repository":{"repo_id":"cambridge","name":"Cambridge University","base_url":"https://api.repository.cam.ac.uk/server/oai/request"},"display":{"title":"Molecular basis of TAPBPR-mediated peptide editing on MHC class I molecules","abstract":"Major histocompatibility complex (MHC) class I molecules present fragments of the cellular proteome, in the form of short peptides, to the cell surface for the inspection by cytotoxic T cells. This process is a crucial immunosurveillance mechanism used to induce appropriate immune responses against intracellular pathogens and cancer. In order to generate optimal T cell-mediated immune responses, prior to their export to the cell surface, MHC class I molecules undergo a process known as peptide selection. Optimal peptide selection is facilitated by two intracellular peptide editors, tapasin and TAPBPR. TAPBPR was shown to shape the peptide repertoire presented on MHC class I at the cell surface, either by directly catalysing peptide exchange on MHC class I molecules or by associating with the quality control enzyme UDP-glycoprotein glucosyltransferase 1 (UGT1), which selects optimally-loaded MHC class I molecules for export to the cell surface. Given that unlike tapasin, TAPBPR could catalyse peptide editing on MHC class I on its own in solution, I sought to test whether TAPBPR could also function as a peptide exchange catalyst on MHC class I molecules present on the surface of cells. By examining the artefactual expression of TAPBPR at the cell surface upon over-expression, I developed two novel cellular assays which allowed me to explore the function of TAPBPR as a peptide exchange catalyst on plasma membrane-expressed MHC class I molecules. I showed that, when given access the cell surface, TAPBPR can promote efficient peptide exchange on surface expressed MHC class I molecules. These assays allowed me to demonstrate that the 22-35 loop of TAPBPR was essential for its peptide exchange function. Moreover, I revealed that residue L30 within the loop was both necessary and sufficient for the efficient ability of TAPBPR to dissociate peptides from MHC class I molecules that typically accommodate hydrophobic anchor residues in their F pocket. This enabled me to propose a new mechanistic model for TAPBPR-mediated peptide editing. I further addressed the molecular basis governing the compatibility between TAPBPR and MHC class I molecules, by screening a wide panel of human leukocyte antigen (HLA) class I allotypes for their relative propensities to undergo peptide editing by TAPBPR. TAPBPR displayed a clear functional preference for HLA-A molecules, particularly for members of the A2 and A24 supertypes, over HLA-B and -C molecules. This preference appears to be driven by specific molecular features of the MHC class I F pocket, in particular residues H114 and Y116. Finally, I explored the potential translational applications of using TAPBPR as a peptide exchange catalyst on surface-expressed MHC class I molecules. I demonstrated that recombinant TAPBPR can be utilised to load immunogenic peptides of choice directly onto plasma-membrane expression MHC class I, thus overriding the internal antigen presentation pathway. Subsequently, I revealed that, TAPBPR can be used to induce T cell-mediated killing of tumour cells. These findings highlight a potential therapeutic application of TAPBPR in increasing the immune recognition of tumours.","abstract_html":"Major histocompatibility complex (MHC) class I molecules present fragments of the cellular proteome, in the form of short peptides, to the cell surface for the inspection by cytotoxic T cells. This process is a crucial immunosurveillance mechanism used to induce appropriate immune responses against intracellular pathogens and cancer. In order to generate optimal T cell-mediated immune responses, prior to their export to the cell surface, MHC class I molecules undergo a process known as peptide selection. Optimal peptide selection is facilitated by two intracellular peptide editors, tapasin and TAPBPR. TAPBPR was shown to shape the peptide repertoire presented on MHC class I at the cell surface, either by directly catalysing peptide exchange on MHC class I molecules or by associating with the quality control enzyme UDP-glycoprotein glucosyltransferase 1 (UGT1), which selects optimally-loaded MHC class I molecules for export to the cell surface. Given that unlike tapasin, TAPBPR could catalyse peptide editing on MHC class I on its own in solution, I sought to test whether TAPBPR could also function as a peptide exchange catalyst on MHC class I molecules present on the surface of cells. By examining the artefactual expression of TAPBPR at the cell surface upon over-expression, I developed two novel cellular assays which allowed me to explore the function of TAPBPR as a peptide exchange catalyst on plasma membrane-expressed MHC class I molecules. I showed that, when given access the cell surface, TAPBPR can promote efficient peptide exchange on surface expressed MHC class I molecules. These assays allowed me to demonstrate that the 22-35 loop of TAPBPR was essential for its peptide exchange function. Moreover, I revealed that residue L30 within the loop was both necessary and sufficient for the efficient ability of TAPBPR to dissociate peptides from MHC class I molecules that typically accommodate hydrophobic anchor residues in their F pocket. This enabled me to propose a new mechanistic model for TAPBPR-mediated peptide editing. I further addressed the molecular basis governing the compatibility between TAPBPR and MHC class I molecules, by screening a wide panel of human leukocyte antigen (HLA) class I allotypes for their relative propensities to undergo peptide editing by TAPBPR. TAPBPR displayed a clear functional preference for HLA-A molecules, particularly for members of the A2 and A24 supertypes, over HLA-B and -C molecules. This preference appears to be driven by specific molecular features of the MHC class I F pocket, in particular residues H114 and Y116. Finally, I explored the potential translational applications of using TAPBPR as a peptide exchange catalyst on surface-expressed MHC class I molecules. I demonstrated that recombinant TAPBPR can be utilised to load immunogenic peptides of choice directly onto plasma-membrane expression MHC class I, thus overriding the internal antigen presentation pathway. Subsequently, I revealed that, TAPBPR can be used to induce T cell-mediated killing of tumour cells. These findings highlight a potential therapeutic application of TAPBPR in increasing the immune recognition of tumours.","abstract_has_math":false,"creators":["Ilca, Florin Tudor"],"institution":"University of Cambridge","degree_name":"Doctor of Philosophy (PhD)","degree_level":"Doctoral","degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Boyle, Louise"],"committee_chairs":[],"committee_members":[],"year":2020,"date_issued":"2020-05-16","date_published":"2020-05-16","updated_at":"2026-07-22T22:24:00Z","subjects":["molecular immunology","MHC class I","immunosurveillance","tumour immunotherapies","T cell responses","TAPBPR","peptide editing","immunomodulation"],"languages":["en"],"rights":[],"rights_urls":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/25c3ee1b-2e7f-4a19-a0b4-351e97c738e4/download","https://www.rioxx.net/licenses/all-rights-reserved/"],"identifier_entries":[]},"links":{"outbound_url":"https://doi.org/10.17863/CAM.51662","outbound_label":"DOI","outbound_source":"dc:identifier.doi"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Boyle, Louise"]},{"key":"dc:contributor.sponsor","label":"Sponsor","values":["My PhD studentship was integrally funded by Wellcome."]},{"key":"dc:creator","label":"Author","values":["Ilca, Florin Tudor"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.issued","label":"Date","values":["2020-05-16"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["University of Cambridge"]},{"key":"dc:relation.isreferencedby.uri","label":"Dc Relation Isreferencedby URI","values":["https://www.repository.cam.ac.uk/handle/1810/304579"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Doctoral"]},{"key":"dc:type.qualificationname","label":"Dc Type Qualificationname","values":["Doctor of Philosophy (PhD)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["molecular immunology","MHC class I","immunosurveillance","tumour immunotherapies","T cell responses","TAPBPR","peptide editing","immunomodulation"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/25c3ee1b-2e7f-4a19-a0b4-351e97c738e4/download","https://www.rioxx.net/licenses/all-rights-reserved/"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.doi","label":"DOI","values":["10.17863/CAM.51662"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/78be5d26-b2de-43af-8378-66561f26fc1b/download"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Major histocompatibility complex (MHC) class I molecules present fragments of the cellular proteome, in the form of short peptides, to the cell surface for the inspection by cytotoxic T cells. 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Given that unlike tapasin, TAPBPR could catalyse peptide editing on MHC class I on its own in solution, I sought to test whether TAPBPR could also function as a peptide exchange catalyst on MHC class I molecules present on the surface of cells. By examining the artefactual expression of TAPBPR at the cell surface upon over-expression, I developed two novel cellular assays which allowed me to explore the function of TAPBPR as a peptide exchange catalyst on plasma membrane-expressed MHC class I molecules. I showed that, when given access the cell surface, TAPBPR can promote efficient peptide exchange on surface expressed MHC class I molecules. These assays allowed me to demonstrate that the 22-35 loop of TAPBPR was essential for its peptide exchange function. Moreover, I revealed that residue L30 within the loop was both necessary and sufficient for the efficient ability of TAPBPR to dissociate peptides from MHC class I molecules that typically accommodate hydrophobic anchor residues in their F pocket. This enabled me to propose a new mechanistic model for TAPBPR-mediated peptide editing. I further addressed the molecular basis governing the compatibility between TAPBPR and MHC class I molecules, by screening a wide panel of human leukocyte antigen (HLA) class I allotypes for their relative propensities to undergo peptide editing by TAPBPR. TAPBPR displayed a clear functional preference for HLA-A molecules, particularly for members of the A2 and A24 supertypes, over HLA-B and -C molecules. This preference appears to be driven by specific molecular features of the MHC class I F pocket, in particular residues H114 and Y116. Finally, I explored the potential translational applications of using TAPBPR as a peptide exchange catalyst on surface-expressed MHC class I molecules. I demonstrated that recombinant TAPBPR can be utilised to load immunogenic peptides of choice directly onto plasma-membrane expression MHC class I, thus overriding the internal antigen presentation pathway. Subsequently, I revealed that, TAPBPR can be used to induce T cell-mediated killing of tumour cells. 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In order to generate optimal T cell-mediated immune responses, prior to their export to the cell surface, MHC class I molecules undergo a process known as peptide selection. Optimal peptide selection is facilitated by two intracellular peptide editors, tapasin and TAPBPR. TAPBPR was shown to shape the peptide repertoire presented on MHC class I at the cell surface, either by directly catalysing peptide exchange on MHC class I molecules or by associating with the quality control enzyme UDP-glycoprotein glucosyltransferase 1 (UGT1), which selects optimally-loaded MHC class I molecules for export to the cell surface. Given that unlike tapasin, TAPBPR could catalyse peptide editing on MHC class I on its own in solution, I sought to test whether TAPBPR could also function as a peptide exchange catalyst on MHC class I molecules present on the surface of cells. By examining the artefactual expression of TAPBPR at the cell surface upon over-expression, I developed two novel cellular assays which allowed me to explore the function of TAPBPR as a peptide exchange catalyst on plasma membrane-expressed MHC class I molecules. I showed that, when given access the cell surface, TAPBPR can promote efficient peptide exchange on surface expressed MHC class I molecules. These assays allowed me to demonstrate that the 22-35 loop of TAPBPR was essential for its peptide exchange function. Moreover, I revealed that residue L30 within the loop was both necessary and sufficient for the efficient ability of TAPBPR to dissociate peptides from MHC class I molecules that typically accommodate hydrophobic anchor residues in their F pocket. This enabled me to propose a new mechanistic model for TAPBPR-mediated peptide editing. I further addressed the molecular basis governing the compatibility between TAPBPR and MHC class I molecules, by screening a wide panel of human leukocyte antigen (HLA) class I allotypes for their relative propensities to undergo peptide editing by TAPBPR. TAPBPR displayed a clear functional preference for HLA-A molecules, particularly for members of the A2 and A24 supertypes, over HLA-B and -C molecules. This preference appears to be driven by specific molecular features of the MHC class I F pocket, in particular residues H114 and Y116. Finally, I explored the potential translational applications of using TAPBPR as a peptide exchange catalyst on surface-expressed MHC class I molecules. I demonstrated that recombinant TAPBPR can be utilised to load immunogenic peptides of choice directly onto plasma-membrane expression MHC class I, thus overriding the internal antigen presentation pathway. Subsequently, I revealed that, TAPBPR can be used to induce T cell-mediated killing of tumour cells. 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