Experimental structures of antibody/MHC-I complexes reveal details of epitopes overlooked by computational prediction

Monoclonal antibodies (mAb) to major histocompatibility complex class I (MHC-I) molecules have proved to be crucial reagents for tissue typing and fundamental studies of immune recognition. To augment our understanding of epitopic sites seen by a set of anti-MHC-I mAb, we determined X-ray crystal structures of four complexes of anti-MHC-I antigen-binding fragments (Fab) bound to peptide/MHC-I/{beta}2m (pMHC-I). An anti-H2-Dd mAb, two anti-MHC-I 3 domain mAb, and an anti-{beta}2-microglobulin ({beta}2m) mAb bind pMHC-I at sites consistent with earlier mutational and functional experiments, and the structures explain allelomorph specificity. Comparison of the experimentally determined structures with computationally derived models using AlphaFold Multimer (AF-M) showed that although predictions of the individual pMHC-I heterodimers were quite acceptable, the computational models failed to properly identify the docking sites of the mAb on pMHC-I. The experimental and predicted structures provide insight into strengths and weaknesses of purely computational approaches and suggest areas that merit additional attention. ONE SENTENCE SUMMARYX-ray structures of anti-MHC-I/MHC-I complexes define epitopes overlooked by computational prediction.