Structural insights from lipid-bilayer nanodiscs link α-Synuclein membrane-binding modes to amyloid fibril formation

Abstract

The protein α-Synuclein (αS) is linked to Parkinson’s disease through its abnormal aggregation, which is thought to involve cytosolic and membrane-bound forms of αS. Following previous studies using micelles and vesicles, we present a comprehensive study of αS interaction with phospholipid bilayer nanodiscs. Using a combination of NMR-spectroscopic, biophysical, and computational methods, we structurally and kinetically characterize αS interaction with different membrane discs in a quantitative and site-resolved way. We obtain global and residue-specific αS membrane affinities, and determine modulations of αS membrane binding due to αS acetylation, membrane plasticity, lipid charge density, and accessible membrane surface area, as well as the consequences of the different binding modes for αS amyloid fibril formation. Our results establish a structural and kinetic link between the observed dissimilar binding modes and either aggregation-inhibiting properties, largely unperturbed aggregation, or accelerated aggregation due to membrane-assisted fibril nucleation.

Cholesterol is a strong promotor of an α-Synuclein membrane binding mode that accelerates oligomerization

“…This suggests that a tighter and more ordered packing of lipids has a negative impact on the α -Syn bilayer interaction, although the presence of net negative charge is a stronger determinant in the current setup. Our findings are consistent with recent studies reporting that cholesterol has negative effect on α -Syn binding 25 , and with reports finding that bilayer fluidity is an important driver for binding alongside charge 4,42 .…”

“…Likewise, pronounced membrane curvature and smaller lipid head group size seem to promote the interaction of α -Syn 4,6,7 . With this is in mind, there is a notable lack of knowledge regarding α -Syn interaction with cholesterol, the most abundant mammalian component of the plasma membrane (PM).…”

“…The known mutants of α -Syn involved in hereditary early onset of PD are clustered towards the end of the membrane binding N-terminal segment of the protein 4,51 . Of these sequence positions, only A30 and A53 could be directly observed in our results.…”

“…Unfortunately, the role of the interaction between α -Syn and lipid bilayers is unclear as a consistent pattern of behaviour has not been observed (review 3 ). Research, including a recent comprehensive work by Viennet et al 4 , indicate that two important membrane general characteristics are affecting the interaction between α -Syn and lipid membrane; its net charge and physical state. A higher abundance of anionic lipids, like phosphatidylserine (PS) or phosphatidylglycerol (PG), leads to a higher affinity of α -Syn and a slower aggregation 4,5 .…”

Computer simulations of protein–membrane systems

“…aSyn-membrane interactions are well documented by a study carried out from Viennet et al 352 , who combined several experimental and computational technique to characterize various properties of the membrane and of aSyn (Fig. 15).…”