Structural Features of Amyloid Fibrils Formed from the Full-Length and Truncated Forms of Beta-2-Microglobulin Probed by Fluorescent Dye Thioflavin T.

ABSTRACT

The persistence of high concentrations of beta-2-microglobulin (ß2M) in the blood of patients with acute renal failure leads to the development of the dialysis-related amyloidosis. This disease manifests in the deposition of amyloid fibrils formed from the various forms of ß2M in the tissues and biological fluids of patients. In this paper, the amyloid fibrils formed from the full-length ß2M (ß2m) and its variants that lack the 6 and 10 N-terminal amino acids of the protein polypeptide chain (ΔN6ß2m and ΔN10ß2m, respectively) were probed by using the fluorescent dye thioflavin T (ThT). For this aim, the tested solutions were prepared via the equilibrium microdialysis approach. Spectroscopic analysis of the obtained samples allowed us to detect one binding mode (type) of ThT interaction with all the studied variants of ß2M amyloid fibrils with affinity ~104 M-1. This interaction can be explained by the dye molecules incorporation into the grooves that were formed by the amino acids side chains of amyloid protofibrils along the long axis of the fibrils. The decrease in the affinity and stoichiometry of the dye interaction with ß2M fibrils, as well as in the fluorescence quantum yield and lifetime of the bound dye upon the shortening of the protein amino acid sequence were shown. The observed differences in the ThT-ß2M fibrils binding parameters and characteristics of the bound dye allowed to prove not only the difference of the ΔN10ß2m fibrils from other ß2M fibrils (that can be detected visually, for example, by transmission electron microscopy (TEM), but also the differences between ß2m and ΔN6ß2m fibrils (that can not be unequivocally confirmed by other approaches). These results prove an essential role of N-terminal amino acids of the protein in the formation of the ß2M amyloid fibrils. Information about amyloidogenic protein sequences can be claimed in the development of ways to inhibit ß2M fibrillogenesis for the treatment of dialysis-related amyloidosis.