title: Surface characterization of insulin protofilaments and fibril polymorphs using tip-enhanced Raman spectroscopy (TERS).
abstract: Amyloid fibrils are β-sheet-rich protein aggregates that are strongly associated with a variety of neurodegenerative maladies, such as Alzheimer's and Parkinson's diseases. Even if the secondary structure of such fibrils is well characterized, a thorough understanding of their surface organization still remains elusive. Tip-enhanced Raman spectroscopy (TERS) is one of a few techniques that allow the direct characterization of the amino acid composition and the protein secondary structure of the amyloid fibril surface. Herein, we investigated the surfaces of two insulin fibril polymorphs with flat (flat) and left-twisted (twisted) morphology. It was found that the two differ substantially in both amino acid composition and protein secondary structure. For example, the amounts of Tyr, Pro, and His differ, as does the number of carboxyl groups on the respective surfaces, whereas the amounts of Phe and of positively charged amino and imino groups remain similar. In addition, the surface of protofilaments, the precursors of the mature flat and twisted fibrils, was investigated using TERS. The results show substantial differences with respect to the mature fibrils. A correlation of amino acid frequencies and protein secondary structures on the surface of protofilaments and on flat and twisted fibrils allowed us to propose a hypothetical mechanism for the propagation to specific fibril polymorphs. This knowledge can shed a light on the toxicity of amyloids and define the key factors responsible for fibril polymorphism. Finally, this work demonstrates the potential of TERS for the surface characterization of amyloid fibril polymorphs.
authors.affiliation: Department of Chemistry, University at Albany, SUNY, Albany, New York; Department of Chemistry, Northwestern University, Evanston, Illinois.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Kurouski
authors.affiliation: Institute of Photonic Technology, Jena, Germany.
authors.forename: Tanja
authors.initials: T
authors.lastname: Deckert-Gaudig
authors.affiliation: Institute of Photonic Technology, Jena, Germany; Institute for Physical Chemistry and Abbe Center of Photonics, University of Jena, Jena, Germany.
authors.forename: Volker
authors.initials: V
authors.lastname: Deckert
authors.affiliation: Department of Chemistry, University at Albany, SUNY, Albany, New York. Electronic address: ilednev@albany.edu.
authors.forename: Igor K
authors.initials: IK
authors.lastname: Lednev
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D002417:Cattle; D007328:Insulin / Q000737:chemistry*; D058105:Polymerization; D017433:Protein Structure, Secondary; D013059:Spectrum Analysis, Raman
chemical_list: D000596:Amino Acids; D007328:Insulin