Insights into the supramolecular architecture of alfa-synuclein amyloid oligomers

J. IGNACIO GALLEA Y M. SOLEDAD CELEJ

San Miguel de Tucuman

Congreso; XLI Reunion anual de la Sociedad Argentina de Biofísica; 2012

Sociedad Argentina de Biofísica

α-synuclein (AS) amyloid oligomers are considered to be the most toxic species underlying neurodegeneration in Parkinson?s disease. It is already recognized that these prefibrillar intermediates contain β-sheet structural elements that differ from the canonical cross β-sheet conformation of amyloid fibrils1. Indeed, we have shown that AS oligomers adopt an antiparallel β-sheet structure, as opposed to the parallel arrangement present in fibrils2. Compared to the monomer, the N-terminus and the hydrophobic region of the protein to at least position 90 are more solvent protected in the oligomeric form3, and therefore, they are likely involved in early β-sheet interactions. We employed engineered single-cysteine containing AS variants labeled with pyrene-maleimide in order to define the regions involved in cooperatively folded structures as well as to identify intermolecular contacts. The experimental approach is based on the solvatochromic response of the pyrene molecule and on its ability to form excimers depending on the distance between two fluorophores. According to GdmCl denaturation profiles, positions 9 and 18 are shielded from the solvent but they would not be entailed in structured regions. Positions 27 and 90 are also protected from the solvent and have similar denaturation curves. Position 76 shows the most distinctive unfolding transition and an excimer band suggesting that this region is involved in early β-sheet interactions. As expected, the C-terminus is solvent-exposed and unstructured. We expect to obtain a detailed residue-specific picture of the supramolecular arrangement of AS oligomers which may contribute to the understanding of both amyloid aggregation mechanism and oligomer-induced toxicity.