A deep mutational scan of the MHC class I-specific chaperone tapasin
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ABSTRACT:
ORGANISM(S): Homo sapiens
PROVIDER: GSE159247 | GEO | 2020/10/09
REPOSITORIES: GEO
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Project description:TAP-binding protein-related (TAPBPR) facilitates the processing of nascent class I MHC (MHC-I) by (1, chaperone function) acting as a chaperone for misfolded or partially folded MHC-I substrates in the cell and (2, editing function) by catalyzing exchange of low affinity for high affinity antigenic peptides in the MHC-I peptide-binding groove. In cells in which the principal MHC-I-specific chaperone and TAPBPR homologue tapasin has been knocked out, the processing and surface trafficking of the human MHC-I allele HLA-A2 is substantially reduced. Over-expression of TAPBPR can partially replace tapasin and rescue HLA-A2 surface expression. Using this assay as the basis for a fluorescence-based selection, TAPBPR was deep mutationally scanned at 92 positions in the core, at the interface with MHC-I, and on the ‘backside’ distal from where MHC-I binds. Critical regions of TAPBPR for rescue of HLA-A2 processing map to sites that contact the underside of the MHC-I alpha-2 domain and residues that contact the junction between beta-2 microglobulin and alpha-3 domains. Key sites on TAPBPR for chaperone activity therefore scaffold assembly of the MHC-I H chain with beta-2 microglobulin.
2020-03-18 | GSE147137 | GEO
Project description:The loading of high affinity peptides onto nascent class I MHC (MHC-I) molecules is facilitated by chaperones, including the class I-specific chaperone TAP-binding protein-related (TAPBPR). TAPBPR features a loop (amino acids 24-35) that projects towards the empty MHC-I peptide binding groove and rests above the F pocket. The 24-35 loop is much shorter in the closely related homologue tapasin, and therefore may be partly responsible for the unique antigen editing properties of TAPBPR. Previously we reported a deep mutational scan of human TAPBPR focused on the 24-35 loop, and determined the relative effects of single amino acid mutations on binding and peptide-mediated release of the murine H2-Dd MHC-I allomorph. Here, we extend our studies to determine the mutational landscape of the 24-35 loop when TAPBPR binds a human MHC-I allomorph, HLA-A*02:01. The data highlights how TAPBPR affinity can be increased or decreased for different MHC-I allomorphs by tuning the electrostatic complementarity of the 24-35 loop for surfaces on the rim of the peptide-binding groove. By changing the selection pressure from HLA-A2 binding to HLA-A2 loading and processing, we find that TAPBPR is reasonably tolerant of mutations in the 24-35 loop for efficient peptide-MHC-I processing and surface trafficking.
2019-09-01 | GSE126206 | GEO
Project description:TAP-binding protein-related (TAPBPR) is an endoplasmic reticulum-resident chaperone that facilitates class I MHC (MHC-I) processing and peptide loading. TAPBPR has (1) chaperone function to stabilize misfolded or partially folded nascent MHC-I substrates, and (2) editing function, in which it catalyzes the exchange of low affinity for high affinity antigenic peptides in the MHC-I peptide-binding groove. TAPBPR-TM is a chimera of the TAPBPR ectodomain and a canonical TM domain, which escapes the endoplasmic reticulum to reach the cell surface. We reasoned that at the cell surface, TAPBPR-TM is more likely to interact with folded MHC-I and thus surface interactions will be more representative of editing function. When tapasin, a homolog of TAPBPR and the main MHC-I-specific chaperone, is knocked out, surface trafficking of HLA-A2 (a human MHC-I allele) is severely diminished, but surface HLA-A2 levels are rescued by over-expression of TAPBPR-TM. Using this assay as the foundation for a fluorescence-based selection, we deep mutationally scanned 104 positions on TAPBPR-TM to identify sites critical for engaging folded MHC-I.
2023-03-09 | GSE218828 | GEO
Project description:Background Dysregulation of major histocompatibility complex (MHC) class I antigen processing and presentation machinery (APM) components in the tumor as one main molecular mechanism of immune escape leading to deactivation of T cell immune surveillance could be due to post-transcriptional regulation via immune-modulatory microRNAs (miRNA). It is now well established from a variety of studies that several miRNAs could effectively modulate the expression of some MHC class I APM components in tumors. Tapasin is an important APM molecule involved in the association of MHC class I with transporter associated with antigen processing (TAP) and peptide loading. Since so far no detailed investigation of the posttranscriptional regulation of tapasin exists, the aim of this study is to identify and functionally characterize miRNAs targeting tapasin in melanoma. Methods Using miRNA trapping by RNA in vitro affinity purification (miTRAP) and in silico as well as small RNA sequencing, miRNAs will be identified, which bind to the 3'untranslated region (3' UTR) of tapasin. Dual luciferase assays will be performed to determine binding of the miRNA. In silico analysis was performed to predict the effect of miRNAs on the survival of melanoma patients in correlation to tapasin. RT-qPCR, Western blot, flow cytometry and other functional assays were performed after transfecting miRNA mimics in three melanoma cell lines. Results Using the combination strategy of miTRAP and RNA seq we identified miR-155-5p to bind to the 3’UTR of tapasin, which was further confirmed by in silico analysis and dual luciferase reporter assay. Transfection of miR-155-5p mimics demonstrated that miR-155-5p upregulate tapasin protein level, which was accompanied by an upregulation of the MHC class I (HLA-ABC) surface expression. Simultaneously, in several different types of cancer, including melanoma, the expression of miR-155-5p is significantly positively correlated with the patient's survival and HLA-A protein. Conclusion Our data revealed for the first time a positive role of miR-155-5p in the posttranscriptional regulation of tapasin in melanoma and provide further insights into the miR-155-5p-mediated induction of HLA-ABC surface expression. This might lead to a better T cell response, avoidance tumor cell escape, improvement of patients' survival and thus might be a potential therapeutic target.
2024-09-15 | GSE240665 | GEO
Project description:The loading of high affinity peptides onto nascent class I MHC (MHC-I) molecules is facilitated by chaperones, including the class I-specific chaperone TAP-binding protein-related (TAPBPR). NMR experiments reveal that conformational dynamics of specific MHC-I allotypes, especially around regions known to be in physical proximity to the TAPBPR interface, are correlated with TAPBPR binding affinity. HLA-A*02:01 residues in the alpha1 and alpha2 domains were deep mutationally scanned to determine the effects of nearly all single amino acid substitutions on HLA-A2 surface expression and TAPBPR interactions. Surface trafficking, which demands HLA-A2 be properly folded with bound peptide, imposes strict sequence constraints on the HLA-A2 core, surfaces contacting the beta2-microglobulin and alpha3 domains, and on the A, B and F pockets that ‘grip’ peptide anchor residues. However, TAPBPR binding is permissive to many mutations of HLA-A2, both in the core and on the surface, with the exceptions of two conserved clusters of hydrophobic residues that pack the alpha2-1 and alpha2-2 helices against the beta-sheet. TAPBPR binding is therefore dependent on a local conformation of the alpha2 domain, most likely with a widened peptide binding groove based on published crystal structures. Overall, the data are consistent with a conformational selection model for MHC-I/TAPBPR interactions, in which high MHC-I dynamics increases representation in the structural ensemble of appropriate conformers for TAPBPR recognition.
2019-10-30 | GSE128957 | GEO
Project description:The loading of high affinity peptides onto nascent class I MHC (MHC-I) molecules is facilitated by chaperones, including the class I-specific chaperone TAP-binding protein-related (TAPBPR). TAPBPR features a ‘scoop’ loop that projects towards the empty MHC-I peptide binding groove and rests above the F pocket. The scoop loop is not found in the closely related homologue tapasin, and therefore may be partly responsible for the unique antigen editing properties of TAPBPR. A deep mutational scan of the TAPBPR scoop loop defines the relative effects of all single amino acid mutations on binding and peptide-mediated release of the murine H2-Dd MHC-I allomorph. Increased hydrophobic packing between the scoop loop and rim of the peptide binding groove tightens the TAPBPR-MHC-I interaction.
2019-10-31 | GSE118568 | GEO
Project description:The extreme polymorphisms of human leukocyte antigen (HLA) class I proteins result in structural variations in their peptide binding sites to achieve diversity in antigen presentation. External factors could independently constrict or alter HLA class I peptide repertoires. Such effects of the assembly factor tapasin were assessed for HLA-B*44:05 (Y116) and a close variant, HLA-B*44:02 (D116), which have low and high tapasin dependence, respectively, for their cell surface expression. Analyses of the HLA-B*44:05 peptidomes in the presence and absence of tapasin reveal that peptides with C-terminal tryptophans and higher predicted affinities are preferentially selected by tapasin, coincident with reduced frequencies of peptides with other C-terminal amino acids, including leucine. Comparisons of the HLA-B*44:05 and HLA-B*44:02 peptidomes indicate the expected structure-based alterations near the peptide C-termini, but also C-terminal amino acid frequency and predicted affinity changes among the unique and shared peptide groups for B*44:02 and B*44:05. Overall, these findings indicate that the presence of tapasin and the tapasin-dependence of assembly alter HLA class I peptide binding preferences at the peptide C-terminus. The particular C-terminal amino acid preferences that are altered by tapasin are expected to be determined by the intrinsic peptide binding specificities of HLA class I allotypes. Additionally, the findings suggest that tapasin deficiency and reduced tapasin dependence expand the permissive affinities of HLA class I bound peptides, consistent with prior findings that HLA class I allotypes with low tapasin dependence have increased breadth of CD8+ T cell epitope presentation and are more protective in HIV infections.
2024-07-15 | PXD046825 | Pride
Project description:Human CD8+ T cells are the final mediators of autoimmune β-cell destruction in type 1 diabetes. However, their target epitopes have not been demonstrated to be naturally processed and presented by β cells. We therefore performed an epitope discovery study combining HLA Class I peptidomics and transcriptomics strategies. Inflammatory cytokines increased β-cell peptide presentation in vitro, paralleling upregulation of HLA Class I expression. Peptide sources included known β-cell antigens and several insulin granule proteins. Preproinsulin yielded multiple previously described HLA-A2-restricted epitopes. Secretogranin V (SCG5/7B2), proconvertase-2, urocortin-3 and the insulin gene enhancer protein ISL-1 were identified as novel β-cell antigens, which were processed into HLA-A2-restricted epitopes recognized by circulating naïve CD8+ T cells in type 1 diabetic and healthy donors. HLA-A2-bound neo-epitopes were also represented and originated from an alternative mRNA splice isoform (SCG5-009) and from an islet amyloid polypeptide transpeptidation product. This first description of the β-cell HLA peptidome opens new avenues to understand the antigen processing pathways employed by β cells and provides a valuable tool for developing T-cell biomarkers and tolerogenic vaccination strategies.
2018-08-02 | GSE108413 | GEO
Project description:The transporter associated with antigen processing (TAP) translocates peptides from the cytosol into the endoplasmic reticulum (ER) where they are loaded onto major histocompatibility class I (MHC I) molecules. Stable peptide-MHC I complexes travel to the cell surface and present their antigenic cargo to cytotoxic T lymphocytes. As central part of the peptide-loading complex (PLC), TAP is targeted by several viral proteins, which inhibit peptide translocation and thereby impact MHC I-mediated immune responses. However, it is still poorly understood whether the MHC I allotypes are differently affected by TAP inhibition. Here, we show that conditional expression of herpes simplex virus (HSV) ICP47 suppresses surface presentation of the MHC I allotypes HLA-A and HLA-C, but not of HLA-B, while expression of cytomegalovirus (CMV) US6 reduces surface levels of all allotypes. This difference is directly reflected in a specific enrichment of HLA-B molecules at US6 arrested PLC. Since ICP47 and US6 inhibit TAP in different transport-incompetent conformations, our data imply that MHC I allomorphs are preferentially recruited or trapped at the PLC leading to selective downregulation of MHC I surface presentation. Our findings suggest that viral immune evasions not only inhibit peptide supply to the ER by TAP, but also modulate the assembly and chaperone activity of the PLC.
2022-02-17 | PXD027408 | Pride
Project description:Immune surveillance by cytotoxic T cells eliminates tumor cells and cells infected by intracellular pathogens. This process relies on the presentation of antigenic peptides on Major Histocompatibility Complex class I (MHC-I) at the cell surface. The loading of these peptides onto MHC-I depends on the peptide loading complex (PLC) at the endoplasmic reticulum (ER). Here, we uncovered that MHC-I antigen presentation is regulated by ER-associated degradation (ERAD), a protein quality control process essential to clear misfolded and unassembled proteins. An unbiased proteomics screen identified the PLC component Tapasin, essential for peptide loading onto MHC-I, as a substrate of the RNF185/Membralin ERAD complex. Loss of RNF185/MBRL resulted in elevated Tapasin steady state levels and increased MHC-I at the surface of professional antigen presenting cells. We further show that RNF185/MBRL ERAD complex recognizes unassembled Tapasin and limits its incorporation into PLC. These findings establish a novel mechanism controlling antigen presentation and suggest RNF185/Membralin as potential therapeutic targets to modulate immune surveillance.
2024-09-17 | PXD048728 | Pride