Membrane-Bound Structures of Alpha-Synuclein Revealed by Infrared Spectroscopy of Cyanylated Cysteine

Abstract

The neural protein α-synuclein (αS) is known to be involved in the development of Parkinson's disease, but specifics about its structure and function remain to be determined. αS is intrinsically disordered in solution; however, upon interacting with lipid membranes, the N-terminus forms an amphipathic helical structure along the membrane interface while the C-terminus remains unstructured in solution. A thiocyanate probe group has been covalently attached to a number of single-cysteine variants of αS, and IR signals were obtained to investigate the environment and local dynamics of the N-terminal segment of αS. The frequency of the aliphatic CN absorption band of the probe group in the IR spectrum is sensitive to the degree of hydration of the probe, indicating its orientation with respect to the bilayer, while the bandwidth of the CN stretching absorption is sensitive to the ps solvent dynamics surrounding the probe and can report on local rigidification of the structure. Spectra of αS in a number of different lipid systems have provided new information regarding the dynamics and structure of the lipid-bound conformation, including direct evidence for a partially-bound structure in which only the beginning of the N-terminus is associated with the lipid membrane.