biostudies-literatureBrunnberg JDeutsche Forschungsgemeinschaft (DFG)Deutsche ForschungsgemeinschaftEuropean Research Councile2321600121https://www.ebi.ac.uk/biostudies/studies/S-EPMC11145271biostudies-literatureUnknown121(22)Antigen presentation via major histocompatibility complex class I (MHC-I) molecules is essential for surveillance by the adaptive immune system. Central to this process is the peptide-loading complex (PLC), which translocates peptides from the cytosol to the endoplasmic reticulum and catalyzes peptide loading and proofreading of peptide-MHC-I (pMHC-I) complexes. Despite its importance, the impact of individual PLC components on the presented pMHC-I complexes is still insufficiently understood. Here, we used stoichiometrically defined antibody-nanobody complexes and engineered soluble T cell receptors (sTCRs) to quantify different MHC-I allomorphs and defined pMHC-I complexes, respectively. Thereby, we uncovered distinct effects of individual PLC components on the pMHC-I surface pool. KnockProceedings of the National Academy of Sciences of the United States of AmericaDual role of the peptide-loading complex as proofreader and limiter of MHC-I presentation.PMC11145271CRC 1507TA 157/12-1798121Tampe RWinter Cde Wet BBattin CBrunnberg JFruhschulz SCole DKSteinberger PBarends MfalseDual role of the peptide-loading complex as proofreader and limiter of MHC-I presentation.Antigen presentation via major histocompatibility complex class I (MHC-I) molecules is essential for surveillance by the adaptive immune system. Central to this process is the peptide-loading complex (PLC), which translocates peptides from the cytosol to the endoplasmic reticulum and catalyzes peptide loading and proofreading of peptide-MHC-I (pMHC-I) complexes. Despite its importance, the impact of individual PLC components on the presented pMHC-I complexes is still insufficiently understood. Here, we used stoichiometrically defined antibody-nanobody complexes and engineered soluble T cell receptors (sTCRs) to quantify different MHC-I allomorphs and defined pMHC-I complexes, respectively. Thereby, we uncovered distinct effects of individual PLC components on the pMHC-I surface pool. Knock2024-01-01T00:00:00Z2024 May2026-04-08T19:52:07.463Z2026-04-08T14:33:48.608ZS-EPMC111452713877188110.1073/pnas.2321600121