Single-Molecule FRET Reveals Structural Heterogeneity of SDS-Bound α-Synuclein

Upon interaction with SIDS, alpha Syn folds into a structure with two antiparallel alpha-helices. We show from single-molecule FRET that alpha Synn adopts this conformation in an all-or-none fashion below the SIDS critical micelle concentration. Population of the folded species is directly coupled to an increase in alpha-helix content; this suggests that the entire N terminus is involved in the transaction.