Human apolipoprotein C-II forms twisted amyloid ribbons and closed loops

D M Hatters, C E MacPhee, L J Lawrence, W H Sawyer, G J Howlett, Cait MacPhee

Research output: Contribution to journalArticlepeer-review

Abstract

Human apolipoprotein C-II (apoC-II) self-associates in solution to form aggregates with the characteristics of amyloid including red-green birefringence in the presence of Congo Red under cross-polarized light, increased fluorescence in the presence of thioflavin T, and a fibrous structure when examined by electron microscopy. ApoC-II was expressed and purified from Escherichia coli and rapidly exchanged from 5 M guanidine hydrochloride into 100 mM sodium phosphate, pH 7.4, to a final concentration of 0.3 mg/mL. This apoC-II was initially soluble, eluting as low molecular weight species in gel filtration experiments using Sephadex G-50. Circular dichroism (CD) spectroscopy indicated predominantly unordered structure. Upon incubation for 24 h, apoC-II self-associated into high molecular weight aggregates as indicated by elution in the void volume of a Sephadex G-50 column, by rapid sedimentation in an analytical ultracentrifuge, and by increased light scattering. CD spectroscopy indicated an increase in beta-sheet content, while fluorescence emission spectroscopy of the single tryptophan revealed a blue shift and an increase in maximum intensity, suggesting repositioning of the tryptophan into a less polar environment. Electron microscopy of apoC-II aggregates revealed a novel looped-ribbon morphology (width 12 nm) and several isolated closed loops. Like ail of the conserved plasma apolipoproteins, apoC-II contains amphipathic helical regions that account for the increase in ct-helix content on lipid binding. The increase in beta-structure accompanying apoC-II fibril formation paints to an alternative folding pathway and an in vitro system to explore the general tendency of apolipoproteins to form amyloid in vivo.

Original languageEnglish
Pages (from-to)8276-8283
Number of pages8
JournalBiochemistry
Volume39
Issue number28
DOIs
Publication statusPublished - 18 Jul 2000

Keywords

  • LOW-DENSITY LIPOPROTEINS
  • X-RAY-DIFFRACTION
  • ALZHEIMERS-DISEASE
  • HUMAN-PLASMA
  • A-II
  • PROTEIN
  • PEPTIDES
  • FIBRILS
  • LIPASE
  • AGGREGATION

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