Interaction of human alpha-synuclein and Parkinson's disease variants withphospholipids - Structural analysis using site-directed mutagenesis

alpha -Synuclein has been centrally implicated in neurodegenerative disease , and a normal function in developmental synaptic plasticity has been sugge sted by studies in songbirds. A variety of observations suggest the protein partitions between membrane and cytosol, a behavior apparently conferred b y a conserved structural similarity to the exchangeable apolipoproteins. He re we show that the capacity to bind lipids is broadly distributed across e xons 3, 4, and 5 (encoding residues 1-102), Binding to phosphatidylserine-c ontaining vesicles requires the presence of all three exons, while binding to phosphatidic acid can be mediated by any one of the three. Consistent wi th a "class A2" helical binding mechanism, lipid association is disrupted b y introduction of charged residues along the hydrophobic face of the predic ted cu-helix and also by biotinylation of conserved lysines (which line the interfacial region). Circular dichroism spectroscopy reveals a general cor relation between the amount of lipid-induced alpha -helix content and the d egree of binding to PS-containing vesicles. Two point mutations associated with Parkinson's disease have little (A30P) or no (A53T) effect on lipid bi nding or a-helicity. These results are consistent with the hypothesis that alpha -synuclein's normal functions depend on an ability to undergo a large conformational change in the presence of specific phospholipids.