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

EZEQUIEL ARDANAZ; J. IGNACIO GALEA; DIEGO SEBASTIAN VAZQUEZ; CARLOS W. BERTONCINI; JAVIER SANTOS; M. SOLEDAD CELEJ

CABA

Congreso; Reunión Conjunta de Sociedades de Biociencias; 2017

Sociedades de Biociencias

The accumulation of intraneuronal amyloid fibrils mainly formed by the 140-aa presynaptic protein α-synuclein (AS) is a hallmark of Parkinson's disease. Neurotoxicity is largely attributed to prefibrillar oligomeric species rather than to the amyloid fibrils. Structural details of the supramolecular organization of AS oligomers (oAS) are needed for understanding the structure-toxicity relationship underlying their pathogenicity. We previously showed that oligomers formed by the wild-type protein (oWT) adopt a distinct antiparallel β-sheet structure and identified a number of intermolecular contacts, many of those involving the N-terminal region. Bioinformatic analysis led us to hypothesize that the N-terminal region adopts a coiled-coil conformation in the oligomer. Therefore, we designed AS mutants that would increase (X3) or decrease (X2) the coiled-coil propensity. To get structural information at the atomic level, all-atom molecular dynamic simulations using the implicit solvent model were carried out for monomeric WT, X2 and X3 variants. Our results indicate that the first 25 residues acquire -helix structure, in agreement with the helical propensity of this region. In line with our hypothesis, additional simulations of the N-terminal 25-mer peptides of WT and X3 variants demonstrate the tendency of coiled-coil interactions. Infrared experiments indicate that oWT and oX3 have similar secondary structural features whereas oX2 have a reduced content of β-sheet structure demonstrating the importance of N-terminal interactions in oligomerization. We are carrying out complementary fluorescence experiments using pyrene-labeled variants to sense changes in intermolecular proximities within the oligomers in response to the introduced mutations. Our results will provide valuable information on the role of helix-helix interactions on amyloid intermediates formation as well as for the development of molecular models of oAS.