Deep mutational scan of tapasin-TM, a variant of the MHC class 1 chaperone tapasin
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ABSTRACT:
ORGANISM(S): Homo sapiens
PROVIDER: GSE311856 | GEO | 2026/01/26
REPOSITORIES: GEO
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Project description:Tapasin acts as the principal MHC-I-specific chaperone for facilitating folding and antigenic peptide loading of nascent MHC class I substrates in the cell. In cells where tapasin has been knocked out, the processing and surface trafficking of the human MHC-I allele HLA-A2 is substantially reduced. Over-expression of tapasin rescues HLA-A2 surface expression. Using this assay as the basis for a fluorescence-based selection, tapasin was deep mutationally scanned at 108 positions in the core, at the interface with MHC-I, and on the ‘backside’ distal from where MHC-I binds. Critical residues of tapasin for rescue of HLA-A2 processing map to sites that contact the underside of the MHC-I alpha-2 domain, to the surface contacting the MHC-1 beta2m and alpha-3 domains, and to the base of a protruding loop that rests above the peptide-binding groove (but not to the tip of the loop itself).
2020-10-09 | GSE159247 | 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 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:Methylobacterium sp. TM 27 strain:TM 27 Genome sequencing
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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: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
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:Investigation of the repertoire of peptide ligands of highly similar Major Histocompatibility complex (MHC) class I allomorphs differing in tapasin dependence; HLA-B*44:02 (tapasin dependent), HLA-B*44:05 (tapasin independent) and HLA-B*44:05 W147A mutant (tapasin dependent).
2025-06-02 | PXD054743 | Pride
Project description:HLA class I (HLA-I) molecules play a central role for both NK and T-cell responses that prevent serious human cytomegalovirus (HCMV) disease. To create opportunities for viral spread, multifaceted HCMV-encoded immunoevasins target HLA-I. Among these, the glycoprotein US10 is so far insufficiently studied. While US10 has been shown to interfere with HLA-G expression, its ability to block classical HLA-I antigen presentation remains unknown. In this study, we demonstrate that US10 recognizes and binds to all HLA-I (HLA-A,-B,-C,-E,-G) heavy chains. Additionally, impaired recruitment of HLA-I to the peptide loading complex was observed. Notably, the associated effects varied significantly dependent on HLA-I genotype and allotype: i) HLA-A molecules evaded down-regulation by US10, ii) tapasin-dependent HLA-B molecules showed impaired maturation and cell surface expression, iii) β2m-assembled HLA-C, in particular HLA-C*05:01 and -C*12:03, and HLA-G were strongly retained in complex with US10 in the endoplasmic reticulum. These genotype-specific effects on HLA-I were confirmed through unbiased HLA-I ligandome analysis. Thus, the US10-mediated impact on HLA-I results in geno- and allotypic differences in a so far unparalleled and multimodal manner.
2024-07-03 | PXD051190 | Pride