title: Molecular architecture of the MHC I peptide-loading complex: one tapasin molecule is essential and sufficient for antigen processing.
abstract: The loading of antigen-derived peptides onto MHC class I molecules for presentation to cytotoxic T cells is a key process in adaptive immune defense. Loading of MHC I is achieved by a sophisticated machinery, the peptide-loading complex (PLC), which is organized around the transporter associated with antigen processing (TAP) with the help of several auxiliary proteins. As an essential adapter protein recruiting MHC I molecules to TAP, tapasin catalyzes peptide loading of MHC I. However, the exact stoichiometry and basic molecular architecture of TAP and tapasin within the PLC remains elusive. Here, we demonstrate that two tapasin molecules are assembled in the PLC, with one tapasin bound to each TAP subunit. However, one tapasin molecule bound either to TAP1 or TAP2 is sufficient for efficient MHC I antigen presentation. By specifically blocking the interaction between tapasin-MHC I complexes and the translocation complex TAP, the MHC I surface expression is impaired to the same extent as with soluble tapasin. Thus, the proximity of the peptide supplier TAP to the acceptor MHC I is crucial for antigen processing. In summary, the human PLC consists maximally of 2× tapasin-ERp57/MHC I per TAP complex, but one tapasin-ERp57/MHC I in the PLC is essential and sufficient for antigen processing.
authors.affiliation: Institute of Biochemistry, Biocenter and Cluster of Excellence Frankfurt (CEF)-Macromolecular Complexes, Goethe-University Frankfurt, Max-von-Laue-Str. 9, 60438 Frankfurt a.M., Germany.
authors.forename: Sabine
authors.initials: S
authors.lastname: Hulpke
authors.forename: Christoph
authors.initials: C
authors.lastname: Baldauf
authors.forename: Robert
authors.initials: R
authors.lastname: Tampé
mesh_terms: D056704:Adaptive Immunity / Q000276:immunology; D000818:Animals; D017951:Antigen Presentation / Q000276:immunology*; D000941:Antigens / Q000276:immunology; D001665:Binding Sites / Q000276:immunology; D005434:Flow Cytometry; D057809:HEK293 Cells; D015234:HLA-A Antigens / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D015235:HLA-B Antigens / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D015236:HLA-C Antigens / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D006367:HeLa Cells; D015395:Histocompatibility Antigens Class I / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D018448:Models, Immunological; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D011485:Protein Binding / Q000276:immunology; D019704:Protein Disulfide-Isomerases / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000276:immunology; D061987:Sf9 Cells; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology
chemical_list: D000941:Antigens; D015234:HLA-A Antigens; D015235:HLA-B Antigens; D015236:HLA-C Antigens; D015395:Histocompatibility Antigens Class I; D026901:Membrane Transport Proteins; D010455:Peptides; C107762:tapasin; D019704:Protein Disulfide-Isomerases; C085868:PDIA3 protein, human