The Lipid-binding Domain of Wild Type and Mutant -Synuclein

-Synuclein ( S) is linked to Parkinson disease through its deposition in an amyloid fibril formwithin Lewy Body deposits, and by the existence of three S point mutations that lead to early onset autosomal dominant Parkinsonism. The normal function of S is thought to be linked to the ability of the protein to bind to the surface of synaptic vesicles. Upon binding to vesicles, S undergoes a structural reorganization from a dynamic and disordered ensemble to a conformation consisting of a long extended helix. In the presence of small spheroidal detergent micelles, however, this extended helix conformation can convert into a broken helix state, in which a region near the middle of the helix unwinds to form a linker between the two resulting separated helices.Membrane-bound conformations of S likely mediate the function of the protein, but may also play a role in the aggregation and toxicity of the protein. Here we have undertaken a study of the effects of the three known PD-linked mutations on the detergentandmembrane-bound conformations of S, as well as factors that govern the transition of the protein between the extended helix and broken helix states. Using pulsed dipolar ESRmeasurements of distances up to 8.7 nm, we show that all three PD-linked S mutants retain the ability to transition from the broken helix to the extended helix conformation. In addition, we find that the ratio of protein to detergent, rather than just the absolute detergent concentration, determines whether the protein adopts the broken or extended helix conformation.