Fast peptide exchange on major histocompatibility complex class I molecules by acidic stabilization of a peptide-empty intermediate.

The cell biology and biochemistry of peptide exchange on major histocompatibility complex class I (MHC-I) proteins are of great interest in the study of immunodominance, which requires iterative optimization of peptide affinity, and cross-presentation of pathogen and tumor antigens, in which endogenous peptides are exchanged for exogenous ones. Even though several methods exist to catalyze peptide exchange on recombinant MHC-I proteins, the cellular conditions and mechanisms allowing for peptide exchange in vivo remain unclear. Here, we demonstrate that low pH, as present in endosomes, indeed triggers peptide exchange, and we dissect the individual steps of the exchange reaction. We find that low pH stabilizes the peptide-empty forms of MHC-I that occur as intermediates of the exchange reaction, and that is synergizes with dipeptides and with disulfide-mediated stabilization of MHC-I.

Rapid peptide exchange on MHC class I by small molecules elucidates dynamics of bound peptide.

Complexes of peptides with recombinant major histocompatibility complex class I molecules (rpMHCs) are an important tool for T cell detection, isolation, and activation in cancer immunotherapy. The rapid preparation of rpMHCs is aided by peptide exchange, for which several technologies exist. Here, we show peptide exchange with small-molecule alcohols and demonstrate that they accelerate the dissociation of pre-bound peptides, creating a novel method for rapid production of rpMHCs and increasing the understanding of the conformational flexibility of the MHC-bound peptides.