title: Evidence for Intramolecular Antiparallel Beta-Sheet Structure in Alpha-Synuclein Fibrils from a Combination of Two-Dimensional Infrared Spectroscopy and Atomic Force Microscopy.
abstract: The aggregation of the intrinsically disordered protein alpha-synuclein (αS) into amyloid fibrils is thought to play a central role in the pathology of Parkinson's disease. Using a combination of techniques (AFM, UV-CD, XRD, and amide-I 1D- and 2D-IR spectroscopy) we show that the structure of αS fibrils varies as a function of ionic strength: fibrils aggregated in low ionic-strength buffers ([NaCl] ≤ 25 mM) have a significantly different structure than fibrils grown in higher ionic-strength buffers. The observations for fibrils aggregated in low-salt buffers are consistent with an extended conformation of αS molecules, forming hydrogen-bonded intermolecular β-sheets that are loosely packed in a parallel fashion. For fibrils aggregated in high-salt buffers (including those prepared in buffers with a physiological salt concentration) the measurements are consistent with αS molecules in a more tightly-packed, antiparallel intramolecular conformation, and suggest a structure characterized by two twisting stacks of approximately five hydrogen-bonded intermolecular β-sheets each. We find evidence that the high-frequency peak in the amide-I spectrum of αS fibrils involves a normal mode that differs fundamentally from the canonical high-frequency antiparallel β-sheet mode. The high sensitivity of the fibril structure to the ionic strength might form the basis of differences in αS-related pathologies.
authors.affiliation: Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Roeters
authors.affiliation: Nanoscale Biophysics Group, FOM Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands.
authors.forename: Aditya
authors.initials: A
authors.lastname: Iyer
authors.affiliation: Nanoscale Biophysics Group, FOM Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands.
authors.forename: Galja
authors.initials: G
authors.lastname: Pletikapić
authors.affiliation: Dannalab BV, Wethouder Beversstraat 185, 7543 BK Enschede, The Netherlands.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Kogan
authors.affiliation: Nanoscale Biophysics Group, FOM Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands.|Vrije Universiteit Amsterdam, De Boelelaan 1105, 1081 HV Amsterdam, The Netherlands.
authors.forename: Vinod
authors.initials: V
authors.lastname: Subramaniam
authors.affiliation: Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
authors.forename: Sander
authors.initials: S
authors.lastname: Woutersen
mesh_terms: D000682:Amyloid / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure; D006801:Humans; D006860:Hydrogen Bonding; D018625:Microscopy, Atomic Force; D009994:Osmolar Concentration; D010300:Parkinson Disease / Q000235:genetics* / Q000473:pathology; D066263:Protein Aggregation, Pathological / Q000235:genetics* / Q000473:pathology; D000072757:Protein Conformation, beta-Strand; D013055:Spectrophotometry, Infrared; D051844:alpha-Synuclein / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure
chemical_list: D000682:Amyloid; D051844:alpha-Synuclein