title: Structural characteristics of alpha-synuclein oligomers stabilized by the flavonoid baicalein.
abstract: The flavonoid baicalein inhibits fibrillation of alpha-synuclein, which is a major component of Lewy bodies in Parkinson's disease. It has been known that baicalein induces the formation of alpha-synuclein oligomers and consequently prevents their fibrillation. In order to evaluate the structural properties of baicalein-stabilized oligomers, we purified oligomer species by HPLC and examined their stability and structure by CD, Fourier transform infrared spectroscopy, size exclusion chromatography HPLC, small-angle X-ray scattering, and atomic force microscopy. Baicalein-stabilized oligomers are beta-sheet-enriched according to CD and Fourier transform infrared spectroscopy analyses. They did not form fibrils even after very prolonged incubation. From small-angle X-ray scattering data and atomic force microscopy images, the oligomers were characterized as quite compact globular species. Oligomers were extremely stable, with a GdmCl C(m)=3.3 M. This high stability explains the previously observed inhibition properties of baicalein against alpha-synuclein fibrillation. These baicalein-stabilized oligomers, added to the solution of aggregating alpha-synuclein, were able to noticeably inhibit its fibrillation. After prolonged coincubation, short fibrils were formed, suggesting an effective interaction of oligomers with monomeric alpha-synuclein. Membrane permeability tests suggested that the baicalein-stabilized oligomers had a mild effect on the integrity of the membrane surface. This effect was rather similar to that of the monomeric protein, suggesting that targeted stabilization of certain alpha-synuclein oligomers might offer a potential strategy for the development of novel Parkinson's disease therapies.
authors.affiliation: Department of Chemistry and Biochemistry, University of California at Santa Cruz, Santa Cruz, CA 95064, USA.
authors.forename: Dong-Pyo
authors.initials: DP
authors.lastname: Hong
authors.forename: Anthony L
authors.initials: AL
authors.lastname: Fink
authors.forename: Vladimir N
authors.initials: VN
authors.lastname: Uversky
mesh_terms: D002942:Circular Dichroism; D004355:Drug Stability; D044950:Flavanones / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D008563:Membrane Lipids / Q000737:chemistry; D018625:Microscopy, Atomic Force; D046529:Microscopy, Electron, Transmission; D010300:Parkinson Disease / Q000188:drug therapy / Q000209:etiology / Q000378:metabolism; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000187:drug effects; D053838:Scattering, Small Angle; D017550:Spectroscopy, Fourier Transform Infrared; D013816:Thermodynamics; D014961:X-Ray Diffraction; D051844:alpha-Synuclein / Q000737:chemistry* / Q000187:drug effects
chemical_list: D044950:Flavanones; D008563:Membrane Lipids; D011994:Recombinant Proteins; D051844:alpha-Synuclein; C006680:baicalein
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