C-terminal unfolding of an amyloidogenic β2-microglobulin fragment: ΔN6β2-microglobulin

Selection of DNA Aptamer That Blocks the Fibrillogenesis of a Proteolytic Amyloidogenic Fragment of β2 m

Dialysis-related amyloidosis (DRA) is a severe complication of hemodialysis that results in progressive destruction of bones and joints. Elevated concentrations of the β₂ -microglobulin (β₂ m) level in the serum of subjects on hemodialysis promote the formation of amyloid fibrils in osteoarticular tissues. β₂ m lacking the N-terminal six residues of the mature protein (ΔN6β₂ m) constitutes 25-30% of β₂ m in ex vivo DRA amyloid. Unlike full-length wild-type β₂ m, ΔN6β₂ m forms amyloid fibrils at neutral pH in vitro. However, the role of ΔN6β₂ m in DRA is, at present, poorly understood. In the present study, we screened novel phosphorothioate-modified aptamers directed against ΔN6β₂ m using combinatorial chemistry in vitro. We identified 11 ΔN6β₂ m aptamers; among the identified aptamers, clone #2, #8, and #10 aptamers had higher binding affinity to ΔN6β₂ m than the others. Biolayer interferometry analysis revealed that K_D values of clone #2, #8, and #10 aptamers were 56, 23, and 44 nM, respectively. Furthermore, the clone #8 aptamer inhibited fibril formation in a dose-dependent manner, as assessed by Thioflavin T fluorescence assay. Fibrils formed from ΔN6β₂ m bind to Congo red, displaying changes in the absorbance spectrum of the dye characteristic of binding to amyloid fibrils, which was completely blocked by treatment with clone #8 aptamer. These results suggest the potential of ΔN6β₂ m aptamers as tools for elucidating co-assembly mechanisms in amyloid formation.