Structural organization of amyloid oligomers of the Parkinson?s disease related protein alfa-synuclein

BERTONCINI CW; CELEJ MS; ARDANAZ E; GALLEA JI

Congreso; AVH-Kolleg, Current Advances on Neurodegeneration: form Molecular Biology to Translational Medicine; 2017

The accumulation of intraneuronalamyloid fibrils mainly formed by the presynaptic protein α-synuclein (AS) is a hallmark of Parkinson's disease.However, nerotoxicity is largy atributed to prefibrillar oligomeric species rather than theinsoluble fibrilar aggregates. Structural details of the supramolecular organization of AS oligomers (oAS) areneeded for understanding the structuretoxicity relationship underlying theirpathogenicity.In previous works from our lab we showed that oAS adopta distinct antiparallel beta-sheetstructure(1) and that they possess a well-defined paƩernof intermolecular contacts(2). Many of these contacts involve regions that form the beta-sheetfibrilar core but, more surprising, we also identified intermolecular proximities within theN-terminal region. Bioinformatic analysis led us to hypothesize that the N-terminal region might adopt acoiled-coil conformation in the oligomeric conformation. In order to test this idea, we rationallydesigned AS mutants that modulate (increase/decrease) the coiled-coil propensity of theN-terminal portion of the protein. We used infrared spectroscopy to assess the changes in secondarystructure of oAS induced by these mutations. In addition, we employed a cystein AS variantspecifically labeled with pyrene-maleimide atposition 9 to get information about intermolecular contacts within theoligomer. The ability of pyrene to form distancedependent excimers allowed us to monitor the changes in intermolecular proximities in neighboring monomers within the aggregate.We anticipate that our results would provide valuableinformation on the role of helix-helixinteractions on prefibrilar amyloid intermediates formationas well as for the development of molecular models of oAS.