Single Molecule FRET On Alpha Synuclein Membrane-bound Conformational States

Abstract

Alpha-Synuclein (αS) is the primary component of the Lewy body plaques that are characteristic of Parkinson's disease (PD). Large insoluble αS aggregates compose Lewy bodies, but smaller soluble αS oligomers are implicated as the cytotoxic species in PD. Though αS is natively unstructured in solution, it forms a N-terminal alpha helix upon binding to lipid membranes. Extensive evidence also shows that αS gains structure upon forming oligomeric species. In order to learn more about the transition of monomeric αS to toxic oligomeric species and to identify critical conformational states along this pathway, we use single molecule Forster resonance energy transfer (smFRET) and fluorescence correlation spectroscopy (FCS) to characterize the monomeric conformational states of αS. Our evidence shows that αS populates at least two distinct, monomeric conformational states, as a function of curvature, on lipid membranes or lipid mimetics. This could mean αS forms distinct conformations based on whether it binds synaptic vesicles or other cellular membranes. Perhaps one of these conformations is more susceptible to conversion to toxic species, and so this finding may enhance our understanding of how toxic oligomers are formed in PD.