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?-Synuclein-induced tubule formation in lipid bilayers.

ABSTRACT: ?-Synuclein is a presynaptic protein that binds to phospholipid membranes and is involved in the pathogenesis of Parkinson's disease (PD). In this paper, we describe the effects of adding wild-type ?-synuclein (WT) and three familial PD mutants (A53T, A30P, and E46K) to membranes containing 15-35 mol % anionic lipid. Tubules were observed to form in the membranes to an extent that depended on the ?-synuclein variant, the anionic lipid content, and the protein concentration. For all four variants, tubule formation decreased with increasing anionic lipid content. Tubules were more readily observed with A30P and E46K than with WT or A53T. The results are consistent with a model wherein the helical content of ?-synuclein increases with increasing anionic lipid content, and ?-synuclein conformers with low helical content have a high propensity to induce tubule formation. This work, combined with previous work from our laboratory (Pandey et al. Biophys. J. 2009, 96, 540), shows that WT adsorption of the protein has deleterious effects on the membrane when the anionic lipid concentration is less than 30 mol % (tubule formation) or greater than 40 mol % (reorganization of the bilayer, clustering of protein).

SUBMITTER: Pandey AP

PROVIDER: S-EPMC3098118 | biostudies-literature | 2011 May

REPOSITORIES: biostudies-literature

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α-Synuclein-induced tubule formation in lipid bilayers.

Pandey Anjan P AP Haque Farzin F Rochet Jean-Christophe JC Hovis Jennifer S JS

The journal of physical chemistry. B 20110427 19

α-Synuclein is a presynaptic protein that binds to phospholipid membranes and is involved in the pathogenesis of Parkinson's disease (PD). In this paper, we describe the effects of adding wild-type α-synuclein (WT) and three familial PD mutants (A53T, A30P, and E46K) to membranes containing 15-35 mol % anionic lipid. Tubules were observed to form in the membranes to an extent that depended on the α-synuclein variant, the anionic lipid content, and the protein concentration. For all four variants ...[more]

PMID: 21520980

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Project description:An amyloid form of the protein ?-synuclein is the major component of the intraneuronal inclusions called Lewy bodies, which are the neuropathological hallmark of Parkinson's disease (PD). ?-Synuclein is known to associate with anionic lipid membranes, and interactions between aggregating ?-synuclein and cellular membranes are thought to be important for PD pathology. We have studied the molecular determinants for adsorption of monomeric ?-synuclein to planar model lipid membranes composed of zwitterionic phosphatidylcholine alone or in a 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 two complementary techniques-quartz crystal microbalance with dissipation monitoring, and neutron reflectometry. We found that the interaction and adsorbed conformation depend on membrane charge, protein charge, and electrostatic screening. The results imply that ?-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 that is 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 the level of ?-synuclein adsorption with a reduced water content in the acyl chain layer. In conclusion, the association of ?-synuclein to membranes and its adsorbed conformation are of electrostatic origin, combined with van der Waals interactions, but with a very weak correlation to the molecular structure of the anionic lipid headgroup. The perturbation of the acyl chain packing upon monomeric protein adsorption favors association with unsaturated phospholipids preferentially found in the neuronal membrane.

Project description:Most plasma membranes comprise a large number of different molecules including lipids and proteins. In the standard fluid mosaic model, the membrane function is effected by proteins whereas lipids are largely passive and serve solely in the membrane cohesion. Here we show, using supported 1,2-dioleoyl-sn-glycero-3-phosphocholine lipid bilayers in different saline solutions, that ions can locally induce ordering of the lipid molecules within the otherwise fluid bilayer when the latter is supported. This nanoordering exhibits a characteristic length scale of ?20 nm, and manifests itself clearly when mechanical stress is applied to the membrane. Atomic force microscopy (AFM) measurements in aqueous solutions containing NaCl, KCl, CaCl2, and Tris buffer show that the magnitude of the effect is strongly ion-specific, with Ca2+ and Tris, respectively, promoting and reducing stress-induced nanotexturing of the membrane. The AFM results are complemented by fluorescence recovery after photobleaching experiments, which reveal an inverse correlation between the tendency for molecular nanoordering and the diffusion coefficient within the bilayer. Control AFM experiments on other lipids and at different temperatures support the hypothesis that the nanotexturing is induced by reversible, localized gel-like solidification of the membrane. These results suggest that supported fluid phospholipid bilayers are not homogenous at the nanoscale, but specific ions are able to locally alter molecular organization and mobility, and spatially modulate the membrane's properties on a length scale of ?20 nm. To illustrate this point, AFM was used to follow the adsorption of the membrane-penetrating antimicrobial peptide Temporin L in different solutions. The results confirm that the peptides do not absorb randomly, but follow the ion-induced spatial modulation of the membrane. Our results suggest that ionic effects have a significant impact for passively modulating the local properties of biological membranes, when in contact with a support such as the cytoskeleton.

Project description:BackgroundResponse guided treatment in breast cancer is highly desirable, but the effectiveness is only established based on residual cellularity from histopathological analysis after surgery. Tubule formation, a key component of grading score, is directly associated with cellularity, with significant implications on prognosis. Peri-tumoural lipid composition, a potential marker, can be rapidly mapped across the entire breast using novel method of chemical shift-encoded imaging, enabling the quantification of spatial distribution. We hypothesise that peri-tumoural spatial distribution of lipid composition is sensitive to tumour cellular differentiation and proliferative activity.MethodsTwenty whole tumour specimens freshly excised from patients with invasive ductal carcinoma (9 Score 2 and 11 Score 3 in tubule formation) were scanned on a 3 T clinical scanner (Achieva TX, Philips Healthcare). Quantitative lipid composition maps were acquired for polyunsaturated, monounsaturated, and saturated fatty acids (PUFA, MUFA, SFA). The peri-tumoural spatial distribution (mean, skewness, entropy and kurtosis) of each lipid constituent were then computed. The proliferative activity marker Ki-67 and tumour-infiltrating lymphocytes (TILs) were assessed histologically.ResultsFor MUFA, there were significant differences between groups in mean (p = 0.0119), skewness (p = 0.0116), entropy (p = 0.0223), kurtosis (p = 0.0381), and correlations against Ki-67 in mean (ρ = -0.5414), skewness (ρ = 0.6045) and entropy (ρ = 0.6677), and TILs in mean (ρ = -0.4621). For SFA, there were significant differences between groups in mean (p = 0.0329) and skewness (p = 0.0111), and correlation against Ki-67 in mean (ρ = 0.5910). For PUFA, there was no significant difference in mean, skewness, entropy or kurtosis between the groups.ConclusionsThere was an association between peri-tumoural spatial distribution of lipid composition with tumour cellular differentiation and proliferation. Peri-tumoural lipid composition imaging might have potential in non-invasive quantitative assessment of patients with breast cancer for treatment planning and monitoring.

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?-Synuclein-induced tubule formation in lipid bilayers.

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α-Synuclein-induced tubule formation in lipid bilayers.

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