Flow-induced alignment of amyloid protofilaments revealed by linear dichroism

Abstract

Amyloid fibrils underlying various serious amyloidoses including Alzheimer and prion diseases form characteristic deposits in which linear fibrils with an unbranched and rigid morphology associate laterally or radially, e.g. radial senile amyloid plaques of amyloid β. To clarify the formation of these high order amyloid deposits, studying the rheology is important. A 22-residue K3 peptide fragment of β2-microglobulin, a protein responsible for dialysis-related amyloidosis, forms long and homogeneous protofilament-like fibrils in 20% (v/v) 2,2,2-trifluoroethanol and 10 mM HCl (pH ∼2). Here, using circular dichroism and linear dichroism, we observed the flow-induced alignment of fibrils. Analysis of far- and near-UV linear dichroism spectra suggested that both the net π-π* transition moment of the backbone carbonyl group and Lb transition moment of the Tyr26 side chain are oriented in parallel to the fibril axis, revealing the structural details of amyloid protofilaments. Moreover, the intensities of flow-induced circular dichroism or linear dichroism signals depended critically on the length and type of fibrils, suggesting that they are useful for detecting and characterizing amyloid fibrils. © 2007 by The American Society for Biochemistry and Molecular Biology, Inc.