A Topological Model of the Interaction between α-Synuclein and Sodium Dodecyl Sulfate Micelles

Abstract

Human alpha-synuclein is a 140-amino acid protein of unknown function abundantly expressed in the brain and found in Lewy bodies, a characteristic feature of Parkinson's disease. Alpha-synuclein is random in water under physiological conditions, but the first approximately 100 residues interact with SDS micelles or acidic phospholipid small unilamellar vesicles and adopt an ordered conformation. The rest of the molecule remains disordered in the bulk of the solution. The conformation of the N-terminal portion of the molecule in lipids was described as an extended helix [Ramakrishnan, M., Jensen, P. H., and Marsh, D. (2003) Biochemistry 42, 12919-12926], as two distinct alpha-helices interrupted by a two-residue break [Chandra, S., Chen, X., Rizo, J., Jahn, R., and Sudhof, T. C. (2003) J. Biol. Chem. 278, 15313-15318], or as a noncanonical conformation, the alpha11/3 helix [Bussell, R., Jr., and Eliezer, D. (2003) J. Mol. Biol. 329, 763-778]. We characterized the topology of the different regions of alpha-synuclein relative to the surface of SDS micelles using spin probe-induced broadening of NMR signals, (15)N relaxation measurements, and fluorescence spectroscopy. Our results support the presence of two N-terminal helices, positioned on the surface of the micelle and separated by a flexible stretch. The region of residues 61-95 of the protein also adopts a helical conformation, but it is partially embedded in the micelle. These results could shed some light on the role of the membrane on the aggregation process of alpha-synuclein.

Micelle-Induced Folding of Spinach Thylakoid Soluble Phosphoprotein of 9 kDa and Its Functional Implications,

“…However, the average R 2 /R 1 ratio of 15.8 determined for residues in the α 1 -helix is in good agreement with values found by others for small peptides in SDS micelles at this field strength (52,(57)(58).…”

A novel coiled-coil repeat variant in a class of bacterial cytoskeletal proteins

“…However, Scy does have several conserved glycines, a notable case being 3 equally spaced 17 residues apart starting at 1111; one or more breaks in the coiled-coil structure are certainly plausible. Also discounted is the glycine-rich, helical, 11-residue repeat of a-synuclein, whose hydrophobic interface interacts directly with micelle membranes (Bisaglia et al, 2005), although computational evidence implies it too may form coiled coils at high concentrations (Mihajlovic and Lazaridis, 2008).…”

Preparation and Characterization of Stable α-Synuclein Lipoprotein Particles

“…Initial studies by solution-state nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy performed in the presence of SDS or anionic small unilamellar vesicles (SUVs), respectively, suggested that the first ϳ100 residues of ␣-Syn form a single extended helix (5,36). Subsequent NMR data collected of ␣-Syn in complex with SDS proposed an alternative state, often termed horseshoe conformation, consisting of two distinct helices interrupted by a short break (11,(37)(38)(39)(40). While some studies suggested that the horseshoe conformation results from the constraints imposed by the reduced size and higher curvature of detergent micelles (36,41,42), others reported evidence of helix breaking even with SUVs large enough to accommodate the extended helix (43,44).…”