title: Multimodal Spectroscopic Study of Amyloid Fibril Polymorphism.
abstract: Amyloid fibrils are a large class of self-assembled protein aggregates that are formed from unstructured peptides and unfolded proteins. The fibrils are characterized by a universal β-sheet core stabilized by hydrogen bonds, but the molecular structure of the peptide subunits exposed on the fibril surface is variable. Here we show that multimodal spectroscopy using a range of bulk- and surface-sensitive techniques provides a powerful way to dissect variations in the molecular structure of polymorphic amyloid fibrils. As a model system, we use fibrils formed by the milk protein β-lactoglobulin, whose morphology can be tuned by varying the protein concentration during formation. We investigate the differences in the molecular structure and composition between long, straight fibrils versus short, wormlike fibrils. We show using mass spectrometry that the peptide composition of the two fibril types is similar. The overall molecular structure of the fibrils probed with various bulk-sensitive spectroscopic techniques shows a dominant contribution of the β-sheet core but no difference in structure between straight and wormlike fibrils. However, when probing specifically the surface of the fibrils with nanometer resolution using tip-enhanced Raman spectroscopy (TERS), we find that both fibril types exhibit a heterogeneous surface structure with mainly unordered or α-helical structures and that the surface of long, straight fibrils contains markedly more β-sheet structure than the surface of short, wormlike fibrils. This finding is consistent with previous surface-specific vibrational sum-frequency generation (VSFG) spectroscopic results ( VandenAkker et al. J. Am. Chem. Soc. , 2011 , 133 , 18030 - 18033 , DOI: 10.1021/ja206513r ). In conclusion, only advanced vibrational spectroscopic techniques sensitive to surface structure such as TERS and VSFG are able to reveal the difference in structure that underlies the distinct morphology and rigidity of different amyloid fibril polymorphs that have been observed for a large range of food and disease-related proteins.
authors.affiliation: FOM Institute AMOLF , Science Park 104, 1098 XG Amsterdam, The Netherlands.
authors.forename: Corianne C
authors.initials: CC
authors.lastname: VandenAkker
authors.affiliation: Department of Molecular Spectroscopy, Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Schleeger
authors.affiliation: FOM Institute AMOLF , Science Park 104, 1098 XG Amsterdam, The Netherlands.
authors.forename: Anne L
authors.initials: AL
authors.lastname: Bruinen
authors.affiliation: Leibniz Institute of Photonic Technology , Albert-Einstein-Straße 9, 07745 Jena, Germany.
authors.forename: Tanja
authors.initials: T
authors.lastname: Deckert-Gaudig
authors.affiliation: Soft Condensed Matter, Debye Institute for Nanomaterials Science, Department of Physics and Astronomy, Utrecht University , Princetonplein 5, 3584 CC Utrecht, The Netherlands.|Unilever R&D Vlaardingen , Olivier van Noortlaan 120, 3130 AC Vlaardingen, The Netherlands.
authors.forename: Krassimir P
authors.initials: KP
authors.lastname: Velikov
authors.affiliation: FOM Institute AMOLF , Science Park 104, 1098 XG Amsterdam, The Netherlands.
authors.forename: Ron M A
authors.initials: RM
authors.lastname: Heeren
authors.affiliation: Leibniz Institute of Photonic Technology , Albert-Einstein-Straße 9, 07745 Jena, Germany.|Institute for Physical Chemistry and Abbe Center of Photonics, University of Jena , Helmholtzweg 4, 07743 Jena, Germany.
authors.forename: Volker
authors.initials: V
authors.lastname: Deckert
authors.affiliation: Department of Molecular Spectroscopy, Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Mischa
authors.initials: M
authors.lastname: Bonn
authors.affiliation: FOM Institute AMOLF , Science Park 104, 1098 XG Amsterdam, The Netherlands.
authors.forename: Gijsje H
authors.initials: GH
authors.lastname: Koenderink
mesh_terms: D000682:Amyloid / Q000138:chemical synthesis / Q000737:chemistry*; D002942:Circular Dichroism; D007782:Lactoglobulins / Q000737:chemistry*; D013058:Mass Spectrometry; D018625:Microscopy, Atomic Force; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman; D013499:Surface Properties
chemical_list: D000682:Amyloid; D007782:Lactoglobulins