Browsing by Author "Masters, CL"

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    Anionic phospholipid interactions of the prion protein N terminus are minimally perturbing and not driven solely by the octapeptide repeat domain
    (American Society for Biochemistry and Molecular Biology, 2010-10-15) Boland, MP; Hatty, CR; Separovic, F; Hill, AF; Tew, DJ; Barnham, KJ; Haigh, CL; James, M; Masters, CL; Collins, SJ
    Although the N terminus of the prion protein (PrPC) has been shown to directly associate with lipid membranes, the precise determinants, biophysical basis, and functional implications of such binding, particularly in relation to endogenously occurring fragments, are unresolved. To better understand these issues, we studied a range of synthetic peptides: specifically those equating to the N1 (residues 23–110) and N2 (23–89) fragments derived from constitutive processing of PrPC and including those representing arbitrarily defined component domains of the N terminus of mouse prion protein. Utilizing more physiologically relevant large unilamellar vesicles, fluorescence studies at synaptosomal pH (7.4) showed absent binding of all peptides to lipids containing the zwitterionic headgroup phosphatidylcholine and mixtures containing the anionic headgroups phosphatidylglycerol or phosphatidylserine. At pH 5, typical of early endosomes, quartz crystal microbalance with dissipation showed the highest affinity binding occurred with N1 and N2, selective for anionic lipid species. Of particular note, the absence of binding by individual peptides representing component domains underscored the importance of the combination of the octapeptide repeat and the N-terminal polybasic regions for effective membrane interaction. In addition, using quartz crystal microbalance with dissipation and solid-state NMR, we characterized for the first time that both N1 and N2 deeply insert into the lipid bilayer with minimal disruption. Potential functional implications related to cellular stress responses are discussed. © 2010, American Society for Biochemistry and Molecular Biology
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    Guanidine hydrochloride denaturation of dopamine-induced α-synuclein oligomers: a small-angle x-ray scattering study
    (Wiley Online Library, 2013-06-4) Pham, CLL; Kirby, N; Wood, K; Ryan, T; Roberts, B; Sokolova, AV; Barnham, KJ; Masters, CL; Knott, RB; Cappai, R; Curtain, CC; Rekas, A
    Alpha-synuclein (α-syn) forms the amyloid-containing Lewy bodies found in the brain in Parkinson's disease. The neurotransmitter dopamine (DA) reacts with α-syn to form SDS-resistant soluble, non-amyloid, and melanin-containing oligomers. Their toxicity is debated, as is the nature of their structure and their relation to amyloid-forming conformers of α-syn. The small-angle X-ray scattering technique in combination with modeling by the ensemble optimization method showed that the un-reacted native protein populated three broad classes of conformer, while reaction with DA gave a restricted ensemble range suggesting that the rigid melanin molecule played an important part in their structure. We found that 6 M guanidine hydrochloride did not dissociate α-syn DA-reacted dimers and trimers, suggesting covalent linkages. The pathological significance of covalent association is that if they are non-toxic, the oligomers would act as a sink for toxic excess DA and α-syn; if toxic, their stability could enhance their toxicity. We argue it is essential, therefore, to resolve the question of whether they are toxic or not. © 2013,Wiley Periodicals, Inc.
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    Structure of dopamine induced α-synuclein oligomers
    (Springer, 2010-3-23) Rekas, A; Knott, RB; Sokolova, AV; Barnham, KJ; Perez, KA; Masters, CL; Drew, SC; Cappai, R; Curtain, CC; Pham, CLL
    Inclusions of aggregated α-synuclein (α-syn) in dopaminergic neurons are a characteristic histological marker of Parkinson’s disease (PD). In vitro, α-syn in the presence of dopamine (DA) at physiological pH forms SDS-resistant non-amyloidogenic oligomers. We used a combination of biophysical techniques, including sedimentation velocity analysis, small angle X-ray scattering (SAXS) and circular dichroism spectroscopy to study the characteristics of α-syn oligomers formed in the presence of DA. Our SAXS data show that the trimers formed by the action of DA on α-syn consist of overlapping worm-like monomers, with no end-to-end associations. This lack of structure contrasts with the well-established, extensive β-sheet structure of the amyloid fibril form of the protein and its pre-fibrillar oligomers. We propose on the basis of these and earlier data that oxidation of the four methionine residues at the C- and N-terminal ends of α-syn molecules prevents their end-to-end association and stabilises oligomers formed by cross linking with DA-quinone/DA-melanin, which are formed as a result of the redox process, thus inhibiting formation of the β-sheet structure found in other pre-fibrillar forms of α-syn. © 2010, Springer.