Curvature Dynamics of α-Synuclein Familial Parkinson Disease Mutants

Abstract

␣-Synuclein remains a protein of interest due to its propensity to form fibrillar aggregates in neurodegenerative disease and its putative function in synaptic vesicle regulation. Herein, we present a series of atomistic molecular dynamics simulations of wild-type ␣-synuclein and three Parkinson disease familial mutants (A30P, A53T, and E46K) in two distinct environments. First, in order to match recent NMR experiments, we have simulated each protein bound to an SDS detergent micelle. Second, in order to connect more closely to the true biological environment, we have simulated the proteins bound to a 1,2-dioleoylsn-glycero-3-phosphoserine lipid bilayer. In the micelle-bound case, we find that the wild type and all of the variants of ␣-synuclein flatten the underlying micelle, decreasing its surface area. A30P is known to lessen ␣-synuclein/membrane affinity and, consistent with experiment, destabilizes the simulated secondary structure. In the case of A53T, our simulations reveal a range of stabilizing hydrogen bonds that form with the threonine. In both environments, the E46K mutation, which is known to increase bilayer affinity, leads to an additional hydrogen bond between the protein and either the detergent or lipid. Simulations indicate that ␣S and its variants are less dynamic in the bilayer than in the micelle. Furthermore, the simulations of the mutants suggest how changes in the structure and dynamics of ␣-synuclein may affect its biological role. The main component of fibrous inclusions known as Lewy bodies and Lewy neurites, ␣-synuclein (␣S)2 plays a critical, although as yet not fully understood, role in the onset of Parkinson disease (PD) (1). Three point mutations of ␣S, namely A53T, A30P, and E46K, have been correlated with familial PD (2-4), although it is still unclear exactly how these mutations trigger the disease (5-8). In the case of A30P, a set of recent NMR studies suggest that the proline substitution significantly increases the structural dynamics of the protein when bound to an SDS detergent micelle (9, 10). It is widely accepted that this mutant has reduced binding affinity for membranes, although the extent is somewhat controversial (9,(11)(12)(13)(14)(15)(16)(17). The change in membrane affinity is correlated with a decrease in the helical content of the protein, although again there is considerable debate as to the extent of this effect (9,10,13,16,18). This result is not altogether unexpected; proline disrupts helices due to the loss of a backbone hydrogen bond and steric hindrance between it and neighboring residues (19). The exact effects of proline on a helix, however, can be 2-fold: substitution can cause local unfolding (i.e. total loss of secondary structure) or kinking without loss of helicity. In the case of A30P, current experimental techniques have suggested a loss of helicity upand downstream of the substitution. However, it is still unclear to what extent and where the proline substitution forces unfolding, kinking, or both (9, 10).The other PD familial mutants behave ...

Effect of the A30P mutation on the structural dynamics of micelle-bound αSynuclein released in water: a molecular dynamics study

“…In aS, this mutation has been found to cause several interesting alterations to the protein's intrinsic structural dynamics (Bussell and Eliezer 2004;. Experiments and simulations indicate that in a lipid environment it gives rise to destabilization upstream and downstream from the mutation site (Bussell and Eliezer 2004;, and reduces helical propensity and lipid binding affinity (Jensen et al 1998;Jo et al 2002;Perlmutter et al 2009). The strong interactions of WT aS when bound to micelles are found to induce strain in the protein structure which is released with the A30P mutation .…”

Protein-Protein interactions leading to aggregation: Perspectives on mechanism, significance and control

“…As a last example of these studies, simulations should be mentioned in which membrane models have been used for abeta [152] and synuclein [153] in order to determine their possible deleterious effects on biological membranes.…”

Conformational heterogeneity of α -synuclein in membrane

“…Prior MD studies have given us additional insight into the role membranes play in αS function. An atomistic MD study investigated the membrane-bound form of a broken-helix structure by initially placing it within the membrane, suggesting that neighboring glycine residues are the flexible segments of membrane-bound αS [52]. Other studies have focused on the pore-formation of αS aggregates [28, 53], membrane binding of the N-terminus [48], or the membrane curvature induced by binding of αS [54].…”

“…Earlier atomistic simulations of the conformational dynamics of αS initially placed αS within the bilayer, and removed lipids to accommodate the added bulk [52]. In this context, the slow dynamics of lipid molecules, D ~ 8 × 10 −8 cm 2 s −1 [55, 56], poses a problem, as the slow lipid dynamics restrict membrane reorganization around the protein.…”