title: Calcium(II) selectively induces alpha-synuclein annular oligomers via interaction with the C-terminal domain.
abstract: Alpha-synuclein filaments are the major component of intracytoplasmic inclusion bodies characteristic of Parkinson's disease and related disorders. The process of alpha-synuclein filament formation proceeds via intermediate or protofibrillar species, each of which may be cytotoxic. Because high levels of calcium(II) and other metal ions may play a role in disease pathogenesis, we investigated the influence of calcium and other metals on alpha-synuclein speciation. Here we report that calcium(II) and cobalt(II) selectively induce the rapid formation of discrete annular alpha-synuclein oligomeric species. We used atomic force microscopy to monitor the aggregation state of alpha-synuclein after 1 d at 4 degrees C in the presence of a range of metal ions compared with the filament formation pathway in the absence of metal ions. Three classes of effect were observed with different groups of metal ions: (1) Copper(II), iron(III), and nickel(II) yielded 0.8-4 nm spherical particles, similar to alpha-synuclein incubated without metal ions; (2) magnesium(II), cadmium(II), and zinc(II) gave larger, 5-8 nm spherical oligomers; and, (3) cobalt(II) and calcium(II) gave frequent annular oligomers, 70-90 nm in diameter with calcium(II) and 22-30 nm in diameter with cobalt(II). In the absence of metal ions, annular oligomers ranging 45-90 nm in diameter were observed after 10 d incubation, short branched structures appeared after a further 3 wk and extended filaments after 2-3 mo. Previous studies have shown that alpha-synuclein calcium binding is mediated by the acidic C terminus. We found that truncated alpha-synuclein (1-125), lacking the C-terminal 15 amino acids, did not form annular oligomers upon calcium addition, indicating the involvement of the calcium-binding domain.
authors.affiliation: School of Chemistry, Physics and Earth Sciences, Flinders University, Bedford Park, SA 5042, Australia.
authors.forename: Rachel
authors.initials: R
authors.lastname: Lowe
authors.forename: Dean L
authors.initials: DL
authors.lastname: Pountney
authors.forename: Poul Henning
authors.initials: PH
authors.lastname: Jensen
authors.forename: Wei Ping
authors.initials: WP
authors.lastname: Gai
authors.forename: Nicolas H
authors.initials: NH
authors.lastname: Voelcker
mesh_terms: D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D003035:Cobalt / Q000494:pharmacology; D006801:Humans; D008274:Magnesium / Q000494:pharmacology; D018625:Microscopy, Atomic Force; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*; D010446:Peptide Fragments / Q000737:chemistry; D017434:Protein Structure, Tertiary; D051843:Synucleins; D013997:Time Factors; D015032:Zinc / Q000494:pharmacology; D051844:alpha-Synuclein
chemical_list: D009419:Nerve Tissue Proteins; D010446:Peptide Fragments; C497604:SNCA protein, human; D051843:Synucleins; D051844:alpha-Synuclein; D002104:Cadmium; D003035:Cobalt; D008274:Magnesium; D015032:Zinc; D002118:Calcium