Abstract
Misfolding of the protein alpha-synuclein (aS), which associates with presynaptic vesicles, has been implicated in the molecular chain of events leading to Parkinson's disease. Here, the structure and dynamics of micelle-bound aS are reported. Val3-Val37 and Lys45-Thr92 form curved alpha-helices, connected by a well ordered, extended linker in an unexpected anti-parallel arrangement, followed by another short extended region (Gly93-Lys97), overlapping the recently identified chaperone-mediated autophagy recognition motif and a highly mobile tail (Asp98-Ala140). Helix curvature is significantly less than predicted based on the native micelle shape, indicating a deformation of the micelle by aS. Structural and dynamic parameters show a reduced helical content for Ala30-Val37. A dynamic variation in interhelical distance on the microsecond timescale is complemented by enhanced sub-nanosecond timescale dynamics, particularly in the remarkably glycine-rich segments of the helices. These unusually rich dynamics may serve to mitigate the effect of aS binding on membrane fluidity. The well ordered conformation of the helix-helix connector indicates a defined interaction with lipidic surfaces, suggesting that, when bound to larger diameter synaptic vesicles, it can act as a switch between this structure and a previously proposed uninterrupted helix.
Highlights
From the ‡Laboratory of Chemical Physics, NIDDK and the ¶Genetic Disease Research Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland 20892
Mixed-micelles in which 70% of the SDS molecules have been replaced by the lipid-like detergent dodecyl phosphocholine (DPC) were compared with SDS-only micelles to assess the influence of micelle chemical makeup on As the titration progresses (aS) structural properties
When comparing the aS backbone HN and N chemical shifts in the presence of an excess of SDS-only micelles and mixed micelles composed of DPC and SDS at a molar ratio of 70:30, most shifts agreed to within Ϯ0.1 and Ϯ1.0 ppm for HN and N nuclei, respectively (Fig. 3 and Supplementary Fig. 4)
Summary
It was suggested that aS interacts with lipid membranes through its repeat region [10, 11] and interactions with small unilamellar vesicles (SUVs) and micelles preferentially containing negatively charged head groups have been documented in vitro [10, 12,13,14]. Helical wheel models have been proposed to describe the interaction of the helix side chains with the membrane surface [12, 18, 19] Besides those qualitative properties no further structural information of the lipid-bound state of aS is available. We elected to resort to smaller diameter micelles, which elicit a similar aS helical content as SUV [12]
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