title: Architecture of polyglutamine-containing fibrils from time-resolved fluorescence decay.
abstract: The disease risk and age of onset of Huntington disease (HD) and nine other repeat disorders strongly depend on the expansion of CAG repeats encoding consecutive polyglutamines (polyQ) in the corresponding disease protein. PolyQ length-dependent misfolding and aggregation are the hallmarks of CAG pathologies. Despite intense effort, the overall structure of these aggregates remains poorly understood. Here, we used sensitive time-dependent fluorescent decay measurements to assess the architecture of mature fibrils of huntingtin (Htt) exon 1 implicated in HD pathology. Varying the position of the fluorescent labels in the Htt monomer with expanded 51Q (Htt51Q) and using structural models of putative fibril structures, we generated distance distributions between donors and acceptors covering all possible distances between the monomers or monomer dimensions within the polyQ amyloid fibril. Using Monte Carlo simulations, we systematically scanned all possible monomer conformations that fit the experimentally measured decay times. Monomers with four-stranded 51Q stretches organized into five-layered β-sheets with alternating N termini of the monomers perpendicular to the fibril axis gave the best fit to our data. Alternatively, the core structure of the polyQ fibrils might also be a zipper layer with antiparallel four-stranded stretches as this structure showed the next best fit. All other remaining arrangements are clearly excluded by the data. Furthermore, the assessed dimensions of the polyQ stretch of each monomer provide structural evidence for the observed polyQ length threshold in HD pathology. Our approach can be used to validate the effect of pharmacological substances that inhibit or alter amyloid growth and structure.
authors.affiliation: Institute of Biochemistry and Biologie and University of Potsdam, 14467 Potsdam. Electronic address: roethch@uni-potsdam.de.
authors.forename: Christoph
authors.initials: C
authors.lastname: Röthlein
authors.affiliation: Department of Theory of Biological Soft Matter Systems, Institute of Theoretical Physics, Free University Berlin, 14195 Berlin.
authors.forename: Markus S
authors.initials: MS
authors.lastname: Miettinen
authors.affiliation: Institute of Biochemistry and Biologie and University of Potsdam, 14467 Potsdam.
authors.forename: Tejas
authors.initials: T
authors.lastname: Borwankar
authors.affiliation: Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, and.
authors.forename: Jörg
authors.initials: J
authors.lastname: Bürger
authors.affiliation: Max Planck Institute for Molecular Genetics, 14195 Berlin, Germany.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Mielke
authors.affiliation: Institute of Chemistry, University of Potsdam, 14467 Potsdam.
authors.forename: Michael U
authors.initials: MU
authors.lastname: Kumke
authors.affiliation: Institute of Biochemistry and Biologie and University of Potsdam, 14467 Potsdam. Electronic address: ignatova@uni-potsdam.de.
authors.forename: Zoya
authors.initials: Z
authors.lastname: Ignatova
mesh_terms: D000682:Amyloid / Q000737:chemistry* / Q000378:metabolism; D005453:Fluorescence; D006801:Humans; D000071058:Huntingtin Protein; D006816:Huntington Disease; D008958:Models, Molecular; D009419:Nerve Tissue Proteins; D010455:Peptides / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017433:Protein Structure, Secondary
chemical_list: D000682:Amyloid; C086055:HTT protein, human; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D010455:Peptides; C097188:polyglutamine
keywords: Amyloid; Computer Modeling; Fluorescence; Fluorescence Resonance Energy Transfer (FRET); Polyglutamine
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