The impact of N-terminal acetylation of αS-synuclein on phospholipid membrane binding and fibril structure

Human alpha synuclein (S) has been shown to be N-terminally acetylated in its physiological state. This modification is proposed to modulate S's function and aggregation into amyloid fibrils. Using bacterially expressed acetylated αS (NTAc-S) and endogenous S (Endo-S) from human erythrocytes, we show that N-terminal acetylation has little impact on S binding to anionic membranes and thus likely not relevant for regulating membrane affinity. N-terminal acetylation does have an effect on αS aggregation, resulting in a narrower distribution of the aggregation lag times and rates. 2D-IR spectra show that acetylation changes the secondary structure of S in fibrils. This difference may arise from the slightly higher helical propensity of acetylated S in solution leading to a more homogenous fibril population with different fibril structure than non-acetylated αS. We speculate that N-terminal acetylation imposes conformational restraints on N-terminal residues in S, thus predisposing S towards specific interactions with other binding partners or alternatively decrease nonspecific interactions.