Interactions of α-synuclein with membranes

SHVADCHAK VV; FALOMIR LOCKHART LJ; PIEVO R; YUSHCHENKO DA; BENNATI M; JOVIN TM

Göttingen

Conferencia; Neurizons 2011; 2011

MMPIbpc-MPIem-Georg August University

Parkinson´s disease is characterized cytopathologically by the deposition in the midbrain of aggregates composed primarily of the presynaptic neuronal protein α-synuclein (AS). Neurotoxicity is currently attributed to oligomeric microaggregates subjected to oxidative modification and promoting mitochondrial and proteasomal dysfunction. Unphysiological binding to membranes of these and other organelles is presumably involved. We performed a systematic in vitro study of effects of membrane charge, phase, curvature, defects and lipid unsaturation on AS binding using model vesicles and AS labeles with a new sensitive solvatochromic fluorescent probe. The interaction of AS with vesicular membranes is fast and reversible. The protein dissociates from neutral membranes upon thermal transition to the Ld phase and transfers to vesicles with higher affinity. The binding of AS to neutral and negatively charged membranes occurs by apparently different mechanisms. Interaction with neutral bilayers requires the presence of membrane defects; binding increases with membrane curvature and rigidity and decreases in the presence of cholesterol. The association to negatively charged membranes is much stronger and much less sensitive to membrane curvature, phase and cholesterol content. The presence of unsaturated lipids increases binding in all cases. The selectivity of membrane binding likely determines localization of AS inside cells. We found that AS binds outer mitochondrial membrane with at least 10-fold stronger affinity than cellular membrane. Orientation of AS in membrane and immersion level were estimated by comparing three AS mutants containing labels at different positions. It appears that AS is oriented parallel to bilayer surface both in model and natural membranes These findings provide insight into the relation between membrane physical properties and AS binding affinity and dynamics that presumably define protein localization in vivo and, thereby, the role of AS in the physiopathology of Parkinson’s disease.