Helix periodicity, topology, and dynamics of membrane‐associated α‐Synuclein

Abstract

The protein ␣-Synuclein (aS) is a synaptic vesicle-associated regulator of synaptic strength and dopamine homeostasis with a pathological role in Parkinson's disease. The normal function of aS depends on a membrane-associated conformation that is adopted upon binding to negatively charged lipid surfaces. Previously we found that the membrane-binding domain of aS is helical and suggested that it may exhibit an unusual structural periodicity. Here we present a study of the periodicity, topology, and dynamics of detergent micelle-bound aS using paramagnetic spin labels embedded in the micelle or attached to the protein. We show that the helical region of aS completes three full turns every 11 residues, demonstrating the proposed 11/3 periodicity. We also find that the membrane-binding domain is partially buried in the micelle surface and bends toward the hydrophobic interior, but does not traverse the micelle. Deeper submersion of certain regions within the micelle, including the unique lysine-free sixth 11-residue repeat, is observed and may be functionally important. There are no long-range tertiary contacts within this domain, indicating a highly extended configuration. The backbone dynamics of the micelle-bound region are relatively uniform with a slight decrease in flexibility observed toward the C-terminal end. These results clarify the topological features of aS bound to membrane-mimicking detergent micelles, with implications for aS function and pathology.Keywords: Synuclein; Parkinson's; amyloid; protein aggregation; membrane-associated proteins; helix periodicity ␣-Synuclein (aS) is a highly conserved presynaptic protein that plays a role in synaptic strength maintenance and dopamine homeostasis. Evidence that aS controls synaptic strength comes from neuronal cell line and knockout mouse models (Abeliovich et al. 2000;Murphy et al. 2000;Cabin et al. 2002;Schluter et al. 2003) that display impaired synaptic response to repetitive stimuli and alterations in the number of reserve pool vesicles, suggesting that aS regulates reserve synaptic vesicles called upon when readily releasable vesicles are exhausted. aS may accomplish this in part by interacting with and regulating phospholipase D (PLD) (Jenco et al. 1998;Ahn et al. 2002;Outeiro and Lindquist 2003;Payton et al. 2004), an enzyme with a purported role in vesicular trafficking (Liscovitch et al. 2000). aS also appears to be involved in regulating intracellular dopamine levels at several points of control. Expression of aS alters synaptic membrane permeability to dopamine by interacting with the human dopamine transporter (hDAT), resulting in withdrawal of hDAT from the external membrane . aS can also block dopamine synthesis by inhibiting tyrosine hydroxylase (Perez et al. 2002). In addition, aS can influence the activity of the vesicular dopamine transporter VMAT2 (Lotharius et al. 2002). Article published online ahead of print. Article and publication date are at

Mechanism of Membrane Interaction and Disruption by α-Synuclein

“…While the interaction of α-Syn with the membrane initially induces an α-helical rich structure, 7 here it was observed that in the absence of cellular partners α-Syn self-aggregates on the bilayer at sub-physiological concentrations (Fig. 2).…”

Oligomeric alpha‐synuclein and its role in neuronal death

“…Although the protein has little structure, it does gain some helical content in the N-terminus when associated with the membrane (2). Its normal role in the cell remains unclear but like a number of other proteins with poorly defined cellular roles, it is mostly known for its association with neurodegenerative diseases.…”

19F NMR studies of α‐synuclein‐membrane interactions

“…1) is a 140 amino-acid, intrinsically-disordered protein associated with Parkinson's disease and other neurodegenerative disorders [1][2][3][4][5][6][7][8] whose function is hypothesized to involve its interaction with membranes. [8][9][10][11][12] The protein binds lipids and anionic detergents through the seven imperfect, cationic, 11-amino acid repeats located in its N-terminal and hydrophobic regions.…”

“…1) is a 140 amino-acid, intrinsically-disordered protein associated with Parkinson's disease and other neurodegenerative disorders [1][2][3][4][5][6][7][8] whose function is hypothesized to involve its interaction with membranes. [8][9][10][11][12] The protein binds lipids and anionic detergents through the seven imperfect, cationic, 11-amino acid repeats located in its N-terminal and hydrophobic regions. [6][7][8][13][14][15][16][17][18][19][20] Electron paramagnetic resonance (EPR) data on its complex with small unilamellar vesicles (SUVs) suggest that the first $100 residues of the monomeric protein adopt an a-helical conformation that lies on the membrane surface.…”

“…[8][9][10][11][12] The protein binds lipids and anionic detergents through the seven imperfect, cationic, 11-amino acid repeats located in its N-terminal and hydrophobic regions. [6][7][8][13][14][15][16][17][18][19][20] Electron paramagnetic resonance (EPR) data on its complex with small unilamellar vesicles (SUVs) suggest that the first $100 residues of the monomeric protein adopt an a-helical conformation that lies on the membrane surface. [21][22][23][24][25] The last $40 residues lack defined structure and do not appear to be involved in membrane interactions.…”