Dimers of D76N-β2-microglobulin display potent anti-amyloid aggregation activity

Self-association of wild-type β2-microglobulin (WT-β2m) into amyloid fibrils is associated with the disorder Dialysis Related Amyloidosis (DRA). In the familial variant D76N-β2m, the single amino acid substitution enhances the aggregation propensity of the protein dramatically and gives rise to a disorder that is independent of renal dysfunction. Numerous biophysical and structural studies on WT- and D76N-β2m have been performed in order to better understand the structure and dynamics of the native proteins and their different potentials to aggregate into amyloid. However, the structural properties of transient D76N-β2m oligomers and their role(s) in assembly remained uncharted. Here we have utilized NMR methods, combined with photo-induced cross-linking, to detect, trap, and structurally characterize transient dimers of D76N-β2m. We show that the cross-linked D76N-β2m dimers have different structures from those previously characterized for the on-pathway dimers of ΔN6-β2m and are unable to assemble into amyloid. Instead, the cross-linked D76N-β2m dimers are potent inhibitors of amyloid formation, preventing primary nucleation and elongation/secondary nucleation when added in sub-stoichiometric amounts with D76N-β2m monomers. The results highlight the specificity of early protein-protein interactions in amyloid formation and show how mapping these interfaces can inform new strategies to inhibit amyloid assembly.