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Deep mutagenesis of HLA-A*02:01 reveals elements of folded structure necessary for MHC-I-specific chaperone interactions and plasma membrane trafficking

ABSTRACT: The loading of high affinity peptides onto nascent class I MHC (MHC-I) molecules is facilitated by chaperones, including the class I-specific chaperone TAP-binding protein-related (TAPBPR). NMR experiments reveal that conformational dynamics of specific MHC-I allotypes, especially around regions known to be in physical proximity to the TAPBPR interface, are correlated with TAPBPR binding affinity. HLA-A*02:01 residues in the alpha1 and alpha2 domains were deep mutationally scanned to determine the effects of nearly all single amino acid substitutions on HLA-A2 surface expression and TAPBPR interactions. Surface trafficking, which demands HLA-A2 be properly folded with bound peptide, imposes strict sequence constraints on the HLA-A2 core, surfaces contacting the beta2-microglobulin and alpha3 domains, and on the A, B and F pockets that ‘grip’ peptide anchor residues. However, TAPBPR binding is permissive to many mutations of HLA-A2, both in the core and on the surface, with the exceptions of two conserved clusters of hydrophobic residues that pack the alpha2-1 and alpha2-2 helices against the beta-sheet. TAPBPR binding is therefore dependent on a local conformation of the alpha2 domain, most likely with a widened peptide binding groove based on published crystal structures. Overall, the data are consistent with a conformational selection model for MHC-I/TAPBPR interactions, in which high MHC-I dynamics increases representation in the structural ensemble of appropriate conformers for TAPBPR recognition.

ORGANISM(S): Homo sapiens

PROVIDER: GSE128957 | GEO | 2019/10/30

REPOSITORIES: GEO

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