Investigation of the interactions between aptamer and misfolded proteins: From monomer and oligomer to fibril by single-molecule force spectroscopy

Increasing knowledge on the understanding interactions of aptamer with misfolded proteins (including monomer, oligomer, and amyloid fibril) is crucial for development of aggregation inhibitors and diagnosis of amyloid diseases. Herein, the interactions of lysozyme monomer-, oligomer-, and amyloid fibril-aptamer were investigated using single-molecule force spectroscopy. The results revealed that the aptamer screened against lysozyme monomer could also bind to oligomer and amyloid fibril, in spite of the recognition at a lower binding probability. It may be attributed to the inherent structural differences of misfolded proteins and the flexible conformationdissociation of aptamer. In addition, dynamic force spectra showed that there were similar dissociation paths in the process of lysozyme monomer-, oligomer-, and amyloid fibril-aptamer complexes. It showed that the dissociation only passed 1 energy barrier from the binding state to the detachment. However, the dynamic parameters suggested that the oligomer- and amyloid fibril-aptamer were more stable than lysozyme monomer-aptamer. The phenomena may result from the exposure of aptamer-recognized sequences on the surface and the electrostatic interactions. This work demonstrated that single-molecule force spectroscopy could be a powerful tool to study the binding behavior of the aptamer with misfolded proteins at single-molecule level, providing abundant information for researches and comprehensive applications of aptamer probes in diagnosis of amyloid diseases.