Dysregulation of the biosynthesis of
cholesterol and other
lipids has been implicated in many neurological diseases, including
Parkinson's disease. Misfolding of α-
synuclein (α-Syn), the main actor in
Parkinson's disease, is associated with changes in a
lipid environment. However, the exact molecular mechanisms underlying
cholesterol effect on α-Syn binding to
lipids as well as α-Syn oligomerization and fibrillation remain elusive, as does the relative importance of
cholesterol compared to other factors. We probed the interactions and fibrillation behaviour of α-Syn using
styrene-
maleic acid nanodiscs, containing zwitterionic and anionic
lipid model systems with and without
cholesterol. Surface plasmon resonance and
thioflavin T fluorescence assays were employed to monitor α-Syn binding, as well as fibrillation in the absence and presence of membrane models. 1 H-15 N-correlated NMR was used to monitor the fold of α-Syn in response to nanodisc binding, determining individual residue apparent affinities for the nanodisc-contained bilayers. The addition of
cholesterol inhibited α-Syn interaction with
lipid bilayers and, however, significantly promoted α-Syn fibrillation, with a more than a 20-fold reduction of lag times before fibrillation onset. When α-Syn bilayer interactions were analysed at an individual residue level by
solution-state NMR, we observed two different effects of
cholesterol. In nanodiscs made of
DOPC, the addition of
cholesterol modulated the NAC part of α-Syn, leading to stronger interaction of this region with the
lipid bilayer. In contrast, in the nanodiscs comprising
DOPC, DOPE and
DOPG, the NAC part was mostly unaffected by the presence of
cholesterol, while the binding of the N and the C termini was both inhibited.