Universal open MHC-I molecules for rapid peptide loading and enhanced complex stability across HLA allotypes

We outline a structure-guided approach for generating conformationally stable, open MHC-I with enhanced ligand exchange kinetics spanning five HLA-A supertypes, all HLA-B supertypes, and oligomorphic HLA-Ib allotypes. We present direct evidence of positive allosteric cooperativity between peptide binding and β₂m association with the heavy chain. We demonstrate that covalently linked β₂m serves as a conformational chaperone to stabilize empty MHC-I molecules in a peptide-receptive state, by promoting an open conformation and preventing intrinsically unstable heterodimers from irreversible aggregation. Our study provides structural and biophysical insights into the conformational properties of MHC-I ternary complexes, improving the design of ultrastable, universal ligand exchange systems and the tool for characterizing TCRs against pathogen-, tumor-, or autoimmune-associated peptide epitopes in a pan-HLA allelic setting.