Protein-Lipid Association and Aggregation in Parkinson's disease – Niels Bohr Institute - University of Copenhagen

Niels Bohr Institute > Calendar > Activities 2013 > Protein-Lipid Associat...

Protein-Lipid Association and Aggregation in Parkinson's disease

Adsorption of a-synuclein to supported lipid bilayers – positioning and role of electrostatics

Erik Hellstrand, Marie Grey, Marie-Louise Ainalem, John Ankner, Trevor Forsyth, Giovanna Fragneto, Michael Haertlein, Marie-Therese Dauvergne, Hanna Nilsson, Patrik Brundin, Sara Linse, Tommy Nylander, Emma Sparr


Abstract: An amyloid form of the protein α-synuclein is the major component of the intraneuronal inclusions called Lewy bodies, which are the neuropathological hallmark of Parkinson’s disease (PD). α-Synuclein is known to associate with anionic lipid membranes, and interactions between aggregating α-synuclein and cellular membranes are thought to be important for PD pathology. Here we studied the molecular determinants for adsorption of monomeric α-synuclein to planar model lipid membranes composed of zwitterionic phosphatidylcholine alone or in mixture with anionic phosphatidylserine relevant for plasma membranes, or anionic cardiolipin relevant for mitochondrial membranes. We studied the adsorption of the protein to supported bilayers, the position of the protein within and outside the bilayer, and structural changes in the model membranes using the complementary techniques quartz crystal microbalance with dissipation monitoring (QCM-D) and neutron reflectometry (NR). We found that the interaction and adsorbed conformation depends on membrane charge, protein charge and electrostatic screening. The results imply that α-synuclein adsorbs in the headgroup region of anionic lipid bilayers with extensions into the bulk, but does not penetrate deeply into or across the hydrophobic acyl chain region. The adsorption to anionic bilayers leads to a small perturbation of the acyl-chain packing independent of anionic headgroup identity. We also explored the effect of changing the area per headgroup in the lipid bilayer by comparing model systems with different degrees of acyl chain saturation. An increase in area per lipid headgroup leads to an increase in α-synuclein adsorption with reduced water content in the acyl chain layer. In conclusion, the association of α-synuclein to membranes and its adsorbed conformation are of strong electrostatic origin, combined with van der Waals interactions, but with very low correlation to the molecular structure of the anionic lipid headgroup. The perturbation of the acyl chain packing upon monomeric protein adsorption is compatible with the increased permeability seen in other studies and favors association with unsaturated phospholipids preferentially found in neuronal membrane.

Andra studien: Selective lipid co-aggregation with a-synuclein fibrils

Erik Hellstrand*, Agnieszka Nowacka*, Daniel Topgaard, Sara Linse, Emma Sparr,

*These authors contributed equally

ABSTRACT: Amyloid deposits from several human diseases have been found to contain membrane lipids. Co-aggregation of lipids and amyloid proteins in amyloid aggregates, and the related extraction of lipids from cellular membranes, can influence structure and function in both the membrane and the formed amyloid deposit. Co-aggregation can therefore have important implications for the pathological consequences of amyloid formation. Still, very little is known about the mechanism behind co-aggregation and molecular structure in the formed aggregates. To address this, we study in vitro co-aggregation by incubating phospholipid model membranes with the Parkinson’s disease-associated protein, a-synuclein, in monomeric form. After aggregation, we find selective spontaneous uptake of phospholipids into the amyloid fibrils. Phospholipid quantification, polarization transfer solid-state NMR and cryo-TEM together reveal selective co-aggregation of phospholipids and α-synuclein in a saturable manner with a strong dependence on lipid composition. At low lipid concentration, there is a close association of phospholipids to the fibril structure, which is apparent from reduced phospholipid mobility and morphological changes in fibril bundling. At higher lipid to protein ratios, additional vesicles adsorb along the fibrils. While interactions between lipids and amyloid-protein are generally discussed within the perspective of different protein species adsorbing to and perturbing the lipid membrane, the current work reveals amyloid formation in the presence of lipids as a co-aggregation process. The interaction leads to the formation of lipid-protein co-aggregates with distinct structure, dynamics and morphology compared to assemblies formed by either lipid or protein alone.

Seminar by: Erik Hellstrand