Abstract
α-Synuclein (αS) is a protein with multiple conformations and interactions. Natively unfolded in solution, αS accumulates as amyloid in neurological tissue in Parkinson disease and interacts with membranes under both physiological and pathological conditions. Here, we used cryoelectron microscopy in conjunction with electron paramagnetic resonance (EPR) and other techniques to characterize the ability of αS to remodel vesicles. At molar ratios of 1:5 to 1:40 for protein/lipid (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol), large spherical vesicles are converted into cylindrical micelles ~50 Å in diameter. Other lipids of the same charge (negative) exhibit generally similar behavior, although bilayer tubes of 150-500 Å in width are also produced, depending on the lipid acyl chains. At higher protein/lipid ratios, discoid particles, 70-100 Å across, are formed. EPR data show that, on cylindrical micelles, αS adopts an extended amphipathic α-helical conformation, with its long axis aligned with the tube axis. The observed geometrical relationship between αS and the micelle suggests that the wedging of its long α-helix into the outer leaflet of a membrane may cause curvature and an anisotropic partition of lipids, leading to tube formation.
Highlights
Membrane fusion and fission events are effected by remodeling proteins
We showed that when large POPG vesicles are exposed to ␣S, the protein adopts an ␣-helical formation as it remodels the vesicles into tubes [51]
We have found with protein/ lipid ratios between 1:10 and 1:40 that most tubes produced are cylindrical micelles, a membrane topology previously described for lipid/detergent mixtures (60 – 62) and for some lipoprotein tubules induced by the endocytic protein endophilin [63]
Summary
Membrane fusion and fission events are effected by remodeling proteins. Results: Using cryoelectron microscopy, we observed the conversion of large spherical lipid vesicles into narrow protein-coated tubes. Its amino acid sequence contains seven 11-residue repeats that are predicted to form amphipathic ␣-helices that mediate its interaction with membranes; in this respect, it is reminiscent of apolipoprotein [37] Further study of the latter structures detected two forms, depending on the experimental conditions and lipids used, viz. 1) an extended helical form (38 – 40) like a curved rod; and 2) a “horseshoe”like form with broken helices that close to hairpins on small vesicles (39 – 45) and SDS micelles [41, 46, 47] These two conformations are reported to co-exist [48, 49] in the same sample preparation, and under some circumstances, more than half of the membrane-interacting region of ␣S can remain unfolded [50]. We used cryo-EM, CD, and EPR spectroscopy in combination with more closely investigated ␣S-induced tubulation of vesicles
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
