title: A structural model for apolipoprotein C-II amyloid fibrils: experimental characterization and molecular dynamics simulations.
abstract: The self-assembly of specific proteins to form insoluble amyloid fibrils is a characteristic feature of a number of age-related and debilitating diseases. Lipid-free human apolipoprotein C-II (apoC-II) forms characteristic amyloid fibrils and is one of several apolipoproteins that accumulate in amyloid deposits located within atherosclerotic plaques. X-ray diffraction analysis of aligned apoC-II fibrils indicated a simple cross-β-structure composed of two parallel β-sheets. Examination of apoC-II fibrils using transmission electron microscopy, scanning transmission electron microscopy, and atomic force microscopy indicated that the fibrils are flat ribbons composed of one apoC-II molecule per 4.7-Å rise of the cross-β-structure. Cross-linking results using single-cysteine substitution mutants are consistent with a parallel in-register structural model for apoC-II fibrils. Fluorescence resonance energy transfer analysis of apoC-II fibrils labeled with specific fluorophores provided distance constraints for selected donor-acceptor pairs located within the fibrils. These findings were used to develop a simple 'letter-G-like' β-strand-loop-β-strand model for apoC-II fibrils. Fully solvated all-atom molecular dynamics (MD) simulations showed that the model contained a stable cross-β-core with a flexible connecting loop devoid of persistent secondary structure. The time course of the MD simulations revealed that charge clusters in the fibril rearrange to minimize the effects of same-charge interactions inherent in parallel in-register models. Our structural model for apoC-II fibrils suggests that apoC-II monomers fold and self-assemble to form a stable cross-β-scaffold containing relatively unstructured connecting loops.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Victoria 3010, Australia.
authors.forename: Chai Lean
authors.initials: CL
authors.lastname: Teoh
authors.forename: Chi L L
authors.initials: CL
authors.lastname: Pham
authors.forename: Nevena
authors.initials: N
authors.lastname: Todorova
authors.forename: Andrew
authors.initials: A
authors.lastname: Hung
authors.forename: Craig N
authors.initials: CN
authors.lastname: Lincoln
authors.forename: Emma
authors.initials: E
authors.lastname: Lees
authors.forename: Yuen Han
authors.initials: YH
authors.lastname: Lam
authors.forename: Katrina J
authors.initials: KJ
authors.lastname: Binger
authors.forename: Neil H
authors.initials: NH
authors.lastname: Thomson
authors.forename: Sheena E
authors.initials: SE
authors.lastname: Radford
authors.forename: Trevor A
authors.initials: TA
authors.lastname: Smith
authors.forename: Shirley A
authors.initials: SA
authors.lastname: Müller
authors.forename: Andreas
authors.initials: A
authors.lastname: Engel
authors.forename: Michael D W
authors.initials: MD
authors.lastname: Griffin
authors.forename: Irene
authors.initials: I
authors.lastname: Yarovsky
authors.forename: Paul R
authors.initials: PR
authors.lastname: Gooley
authors.forename: Geoffrey J
authors.initials: GJ
authors.lastname: Howlett
mesh_terms: D000595:Amino Acid Sequence; D000682:Amyloid / Q000737:chemistry* / Q000648:ultrastructure; D053304:Apolipoprotein C-II / Q000737:chemistry*; D006801:Humans; D018625:Microscopy, Atomic Force; D008956:Models, Chemical; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D020539:Sequence Analysis, Protein; D014961:X-Ray Diffraction
chemical_list: D000682:Amyloid; D053304:Apolipoprotein C-II