Background: ␣B-crystallin is an ATP-independent chaperone that prevents irreversible protein aggregation. Results: Cu(II) binds to the core domain of ␣B-crystallin, induces increased dynamics at the dimer interface, and thus modulates the anti-aggregation properties of the chaperone. Conclusion:The small heat-shock protein ␣B-crystallin is a metal-regulated chaperone. Significance:The results open new perspectives in the field of protein homeostasis and oxidative stress resistance.

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Presentation of antigenic peptides by major histocompatibility complex class II (MHC-II) proteins determines T helper cell reactivity. The MHC-II genetic locus displays a large degree of allelic polymorphism influencing the peptide repertoire presented by the resulting MHC-II protein allotypes. During antigen processing, the human leukocyte antigen (HLA) molecule HLA-DM (DM) encounters these distinct allotypes and catalyzes exchange of the placeholder peptide CLIP by exploiting dynamic features of MHC-II. Here, we investigate 12 highly abundant CLIP-bound HLA-DRB1 allotypes and correlate dynamics to catalysis by DM. Despite large differences in thermodynamic stability, peptide exchange rates fall into a target range that maintains DM responsiveness. A DM-susceptible conformation is conserved in MHC-II molecules, and allosteric coupling between polymorphic sites affects dynamic states that influence DM catalysis. As exemplified for rheumatoid arthritis, we postulate that intrinsic dynamic features of peptide–MHC-II complexes contribute to the association of individual MHC-II allotypes with autoimmune disease.