Interaction between Alpha-Synuclein and Psychosine: Implications for Lewy Body Formation

TITLE: INTERACTION BETWEEN ALPHA SYNUCLEIN AND PSYCHOSINE: IMPLICATIONS FOR LEWY BODY FORMATION. Alpha-synuclein is a protein implicated in an increasing number of diseases. Protein aggregates containing alpha-synuclein known as Lewy bodies, are typically found in Parkinson’s disease and other synucleionopathies. We have found that psychosine accelerates the fibrillization of alpha-synuclein in vitro in a dose-dependent manner. Psychosine is a cationic sphingolipid implicated in Krabbe disease, a lysosomal storage disorder, in which excess of psychosine (D-Galactosylsphingosine) causes severe CNS damages. Also, we found similarities between Krabbe disease and Parkinson’s that are consistent with synucleionopathy hallmarks. Using NMR and ITC measurements, we show that psychosine is a direct ligand of alpha-synuclein and thus of therapeutic interest. This work characterizes the binding sites, affinity and stoichiometry of this interaction. It also reveals individual residue contributions assigned at both N and C-terminals of alpha-synuclein. We find that psychosine may act as alpha-synuclein cross-linker and a C-terminal neutralizing agent. These observations suggest that binding of psychosine triggers aggregation and fibril expansion due to thermodynamically unfavorable and kinetically favorable interactions that remove the energy barriers to alpha-synuclein fibrillization-aggregation formation. Investigating how ligand binding accelerates alpha-synuclein fibrillization is crucial to understanding how alpha-synuclein goes from the soluble to the Lewy body amyloidogenic state. This work contributes to the growing field of protein deposition disorders.