Core and Heterogeneity of β2-Microglobulin Amyloid Fibrils as Revealed by H/D Exchange

Dialysis-related amyloidosis, which occurs in the patients receiving a long-term hemodialysis with high frequency, accompanies the deposition of amyloid fibrils composed of β2-microglobulin (β2-m). In vitro, β2-m forms two kinds of fibrous structures at acidic pH. One is a rigid “mature fibril”, and the other is a flexible thin filament often called an “immature fibril”. In addition, a 22-residue peptide (K3 peptide) corresponding to Ser20 to Lys41 of intact β2-m forms rigid amyloid-like fibrils similar to mature fibrils. We compared the core of these three fibrils at single-residue resolution using a recently developed hydrogen/deuterium (H/D) exchange method with the dissolution of fibrils by dimethylsulfoxide (DMSO). The exchange time-course of these fibrils showed large deviations from a single exponential curve showing that, because of the supramolecular structures, the same residue exists in different environments from molecule to molecule, even in a single fibril. The exchange profiles revealed that the core of the immature fibril is restricted to a narrow region compared to that of the mature fibril. In contrast, all residues were protected from exchange in the K3 fibril, indicating that a whole region of the peptide is engaged in the β-sheet network. These results suggest the mechanism of amyloid fibril formation, in which the core β-sheet formed by a minimal sequence propagates to form a rigid and extensive β-sheet network.