Extent of N-terminus exposure by altered long-range interactions of monomeric alpha-synuclein determines its aggregation propensity

Abstract

21As an intrinsically disordered protein, monomeric alpha synuclein (aSyn) constantly reconfigures and 22 probes the conformational space. Long-range interactions across the protein maintain its solubility 23 and mediate this dynamic flexibility, but also provide residual structure. Certain conformations lead 24 to aggregation prone and non-aggregation prone intermediates, but identifying these within the 25 dynamic ensemble of monomeric conformations is difficult. Herein, we used the biologically relevant 26 calcium ion to investigate the conformation of monomeric aSyn in relation to its aggregation 27 propensity. By using calcium to perturb the conformational ensemble, we observe differences in 28 structure and intra-molecular dynamics between two aSyn C-terminal variants, D121A and pS129, and 29 the aSyn familial disease mutants, A30P, E46K, H50Q, G51D, A53T and A53E, compared to wild-type 30 (WT) aSyn. We observe that the more exposed the N-terminus and the beginning of the NAC region 31 are, the more aggregation prone monomeric aSyn conformations become. N-terminus exposure 32 occurs upon release of C-terminus interactions when calcium binds, but the level of exposure is 33 specific to the aSyn mutation present. There was no correlation between single charge alterations, 34 2 calcium affinity, or the number of ions bound on aSyn's aggregation propensity, indicating that 35 sequence or post-translation modification (PTM)-specific conformational differences between the N-36 and C-termini and the specific local environment mediate aggregation propensity instead. 37Understanding aggregation prone conformations of monomeric aSyn and the environmental 38 conditions they form under will allow us to design new therapeutics targeted to the monomeric 39 protein, to stabilise aSyn in non-aggregation prone conformations, by either preserving long-range 40 interactions between the N-and C-termini or by protecting the N-terminus from exposure. 41 42 or the environment that can destabilise monomeric conformations to favour aggregation will aid in 58 the design of anti-aggregation therapeutics to stabilise the native aSyn conformation. 59 aSyn is a characteristic IDP with high opposing charge at its termini and low overall hydrophobicity 5 . 60Monomeric aSyn has three characteristic main regions; the N-terminus, aar 1-60, which is overall 61 positively charged, the non-amyloid-β component (NAC) region, aar 61-89, is hydrophobic and forms 62 the core of fibrils during aggregation 7 , and the C-terminus, aar 90-140, is a highly negatively charged 63 region which binds metal ions 8 (Figure 1a). To date, six disease-related mutations have been identified 64 in the SNCA gene, encoding the aSyn protein, A30P, E46K, H50Q, G51D, A53T, A53E, which are a 65 hallmark for hereditary autosomal dominant PD and are primarily linked to early age but also late age 66 of onset (H50Q) 9-15 . However, genetic mutations and multiplications of the SNCA gene only account 67for 5-10% of PD cases and the remaining cases are sporadic (idiopathic) an...

The docking of synaptic vesicles on the presynaptic membrane induced by α-synuclein is modulated by lipid composition

“…4e, f ) 14 . The competition between these interactions can be regulated by a number of factors such as local bursts of calcium ions, which favour an extended double-anchor mechanism and mediate the localisation of αS at presynaptic terminals 16 , post-translational modifications, including the phosphorylation of residues Ser 87 73 , Ser 129 74 and Tyr 39 68 , and modifications of the IPM composition (Fig. 3e, f ).…”

Amyloid Oligomers: A Joint Experimental/Computational Perspective on Alzheimer’s Disease, Parkinson’s Disease, Type II Diabetes, and Amyotrophic Lateral Sclerosis

“…A view is emerging, therefore, that the balance between functional and pathological roles of αS are inextricably connected to the equilibrium between ordered and disordered conformations of the region 65 to 97 at the surface of biological membranes . This balance can be influenced by external factors such as pathological mutations, particularly A30P, G51D, and E56K having significant effects on the membrane binding, and PTMs such as phosphorylation of residues Ser 87, Ser 129, and Tyr 39 that also regulate the equilibrium between membrane-bound and detached states of αS (Figure ). A key posttranslational modification for the membrane binding of αS is the N-terminal acetylation, , which is believed to define the predominant form of the protein in vivo and that enhances the α-helical propensity of the N-terminal residues to increase the membrane affinity …”

Modulation of the Interactions Between α-Synuclein and Lipid Membranes by Post-translational Modifications

“…α-Synuclein is subject to multiple post-translational modifications (Figure 4) including acetylation, phosphorylation, ubiquitination, SUMOylation, nitration, truncation, and glycation (49,(95)(96)(97). Much work has been undertaken to understand how these post-translational modifications affect the aggregation of α-synuclein (98). By contrast, the impact of post-translational modifications on the affinity of α-synuclein for biological membranes requires further study.…”