The Addition of an Osmolyte, Trimethylamine N-Oxide Promotes Secondary Structure Heterogeneity Among Amyloid Fibrils

Abstract

We demonstrated that secondary structure heterogeneity was observed among mature amyloid fibrils synthesized by the addition of an osmolyte, called trimethylamine N-oxide (TMAO) by promoting the formation of anti-parallel β-sheet structure along with parallel β-sheet structure. In regards to amyloid fibrils formed in the absence of TMAO, only parallel β-sheet secondary structure was observed. This structural effect was observed regardless of pH. The amyloid fibrils were investigated via Fourier-transform infrared spectroscopy and near-field microscopy, and the characterized by circular dichroism and UV-Vis spectroscopy. Using FTIR spectroscopy, the peak observed at 1630 cm−1 indicates the presence of parallel and/or anti-parallel β-sheet structure and a peak at 1692 cm−1 denotes the presence of anti-parallel β-sheet structure. This latter peak, which appears only in the TMAO-containing fibril solutions, indicates that TMAO promotes anti-parallel β-sheet fibrils in solution.