Molecular determinants of chaperone interactions on MHC-I for folding and antigen repertoire selection.
Andrew C McShanChristine A DevlinSarah A OverallJihye ParkJugmohit S ToorDanai MoschidiDavid Flores-SolisHannah ChoiSarvind M TripathiErik ProckoNikolaos G SgourakisPublished in: Proceedings of the National Academy of Sciences of the United States of America (2019)
The interplay between a highly polymorphic set of MHC-I alleles and molecular chaperones shapes the repertoire of peptide antigens displayed on the cell surface for T cell surveillance. Here, we demonstrate that the molecular chaperone TAP-binding protein related (TAPBPR) associates with a broad range of partially folded MHC-I species inside the cell. Bimolecular fluorescence complementation and deep mutational scanning reveal that TAPBPR recognition is polarized toward the α2 domain of the peptide-binding groove, and depends on the formation of a conserved MHC-I disulfide epitope in the α2 domain. Conversely, thermodynamic measurements of TAPBPR binding for a representative set of properly conformed, peptide-loaded molecules suggest a narrower MHC-I specificity range. Using solution NMR, we find that the extent of dynamics at "hotspot" surfaces confers TAPBPR recognition of a sparsely populated MHC-I state attained through a global conformational change. Consistently, restriction of MHC-I groove plasticity through the introduction of a disulfide bond between the α1/α2 helices abrogates TAPBPR binding, both in solution and on a cellular membrane, while intracellular binding is tolerant of many destabilizing MHC-I substitutions. Our data support parallel TAPBPR functions of 1) chaperoning unstable MHC-I molecules with broad allele-specificity at early stages of their folding process, and 2) editing the peptide cargo of properly conformed MHC-I molecules en route to the surface, which demonstrates a narrower specificity. Our results suggest that TAPBPR exploits localized structural adaptations, both near and distant to the peptide-binding groove, to selectively recognize discrete conformational states sampled by MHC-I alleles, toward editing the repertoire of displayed antigens.
Keyphrases
- single molecule
- binding protein
- molecular dynamics simulations
- magnetic resonance
- cell surface
- stem cells
- immune response
- cystic fibrosis
- mass spectrometry
- molecular dynamics
- bone marrow
- staphylococcus aureus
- dna methylation
- transcription factor
- high resolution
- deep learning
- cross sectional
- genetic diversity
- artificial intelligence