Low Energy Optical Excitations as an Indicator of Structural Changes Initiated at the Termini of Amyloid Proteins

We combine absorption and fluorscence spectroscopy experiments and theoretical modeling to specifically examine the role of termini interactions on the optical properties. Optical absorption and fluorescence is measured for a six-chain amino acid 2Y3J (AIIGLM) which forms a segment of the full amyloid beta 1-40. In order to explore the sensitivity of the optical properties to the termini interactions, the experiments were repeated by acetylating the N-terminus.Although atomic force microscopy experiments indicate the formation of some form of fibrilar or crystal aggregates in both systems, the optical properties are strikingly different - acetylation significantly reduces optical activity between 280-350 nm.