National Center for
3QXD: F54c Hla-dr1 Bound With Clip Peptide
Conformational lability in the class II MHC 310 helix and adjacent extended strand dictate HLA-DM susceptibility and peptide exchange
Proc. Natl. Acad. Sci. U. S. A. (2011) 108 p.19329-19334
HLA-DM is required for efficient peptide exchange on class II MHC molecules, but its mechanism of action is controversial. We trapped an intermediate state of class II MHC HLA-DR1 by substitution of alphaF54, resulting in a protein with increased HLA-DM binding affinity, weakened MHC-peptide hydrogen bonding as measured by hydrogen-deuterium exchange mass spectrometry, and increased susceptibility to DM-mediated peptide exchange. Structural analysis revealed a set of concerted conformational alterations at the N-terminal end of the peptide-binding site. These results suggest that interaction with HLA-DM is driven by a conformational change of the MHC II protein in the region of the alpha-subunit 3(10) helix and adjacent extended strand region, and provide a model for the mechanism of DM-mediated peptide exchange.