Principal component analysis of data from NMR titration experiment of uniformly ¹⁵N labeled amyloid beta (1–42) peptide with osmolytes and phenolic compounds

A simple NMR method to analyze the data obtained by NMR titration experiment of amyloid formation inhibitors against uniformly ¹⁵N-labeled amyloid-β 1–42 peptide (Aβ(1–42)) was described. By using solution nuclear magnetic resonance (NMR) measurement, the simplest method for monitoring the effects of Aβ fibrilization inhibitors is the NMR chemical shift perturbation (CSP) experiment using ¹⁵N-labeled Aβ(1–42). However, the flexible and dynamic nature of Aβ(1–42) monomer may hamper the interpretation of CSP data. Here we introduced principal component analysis (PCA) for visualizing and analyzing NMR data of Aβ(1–42) in the presence of amyloid inhibitors including high concentration osmolytes. We measured ¹H–¹⁵N 2D spectra of Aβ(1–42) at various temperatures as well as of Aβ(1–42) with several inhibitors, and subjected all the data to PCA (PCA-HSQC). The PCA diagram succeeded in differentiating the various amyloid inhibitors, including epigallocatechin gallate (EGCg), rosmarinic acid (RA) and curcumin (CUR) from high concentration osmolytes. We hypothesized that the CSPs reflected the conformational equilibrium of intrinsically disordered Aβ(1–42) induced by weak inhibitor binding rather than the specific molecular interactions.