Core Structure of Amyloid Fibril Proposed from IR-Microscope Linear Dichroism

A new approach for studying a peptide conformation of amyloid fibril has been developed. It is based on infrared linear dichroism analysis using an IR-microscope for aligned amyloid fibril. The polarization directions of amide I and II bands were perpendicular similarly for beta2-microglobulin and its #21-31 peptide. Furthermore, this approach has shown that the #21-31 peptide consists of two C=O bonds in the beta-sheet that makes 0 degrees with the fibril axis, three C=O bonds in the beta-sheet inclined by 27 degrees with respect to the fibril axis, four residues in the random coil by 47 degrees , and two residues in possible beta-bulge structure by 32 degrees . Plausible structures of the amyloid core in the fibril are proposed by taking account of these results.