C-terminal calcium binding of α-synuclein modulates synaptic vesicle interaction

Abstract

Alpha-synuclein is known to bind to small unilamellar vesicles (SUVs) via its N terminus, which forms an amphipathic alpha-helix upon membrane interaction. Here we show that calcium binds to the C terminus of alpha-synuclein, therewith increasing its lipid-binding capacity. Using CEST-NMR, we reveal that alpha-synuclein interacts with isolated synaptic vesicles with two regions, the N terminus, already known from studies on SUVs, and additionally via its C terminus, which is regulated by the binding of calcium. Indeed, dSTORM on synaptosomes shows that calcium mediates the localization of alpha-synuclein at the pre-synaptic terminal, and an imbalance in calcium or alpha-synuclein can cause synaptic vesicle clustering, as seen ex vivo and in vitro. This study provides a new view on the binding of alpha-synuclein to synaptic vesicles, which might also affect our understanding of synucleinopathies.

Effects of alpha‐synuclein post‐translational modifications on metal binding

“…Of all essential metal ions that AS encounters in vivo , the specific interactions of Cu ions with His50 and the N‐terminal group are the most physiologically relevant, given the high affinity for copper at these anchoring sites. Finally, more recent evidence supports an important role for AS in calcium‐dependent vesicular trafficking, associated to AS‐Ca(II) interactions (Lautenschläger et al ). Hence, in the following sections detailed discussions of the interactions of this protein with calcium and copper ions are presented.…”

“…On the other hand, using a microdialysis technique it was proposed that AS binds Ca(II) at the C‐terminal region with a K D = 2–300 μM (Nielsen et al ). However, recent NMR and mass spectrometry results suggest that it can bind up to 6‐8 calcium ions with a K D in the range 21 μM (Lautenschläger et al ). This dissociation constant lies well within the range of physiological pre‐synaptic calcium fluctuations, reaching up to hundreds of micromolar in healthy neurons upon neuronal stimulation.…”

“…Chemical exchange saturation transfer in solution‐state NMR experiments reveal that AS interacts with isolated synaptic vesicles at the N terminus and via its C terminus, which is regulated by the binding of calcium. These findings suggest that under physiological conditions AS might act as a calcium‐dependent modulator of vesicle homeostasis at the pre‐synaptic terminal, with calcium mediating the localization of AS at the pre‐synaptic terminal (Lautenschläger et al ). Moreover, it has been proposed also that AS might play a key role in calcium transfer from endoplasmic reticulum to mitochondria and that this function requires the presence of the C‐terminal domain of the protein (Cali et al ).…”

“…Moreover, it has been proposed also that AS might play a key role in calcium transfer from endoplasmic reticulum to mitochondria and that this function requires the presence of the C‐terminal domain of the protein (Cali et al ). Indeed, an imbalance in calcium or AS can lead to synaptic vesicle clustering, as seen ex vivo and in vitro , suggesting that high levels of calcium and/or AS are key elements to neuronal toxicity (Lautenschläger et al ). In summary, calcium ions emerge as key modulators of the interaction of AS with synaptic vesicles, underscoring the important role they may play under physiological and cell toxicity conditions.…”

The physiological role of α‐synuclein and its relationship to Parkinson’s Disease

“…Consistent with a weak interaction, the protein localizes relatively late to developing synapses in cultured neurons (Withers et al 1997). In vitro, a-synuclein can associate with synaptic vesicles (Nakamura et al 2008) and Ca ++ has been suggested to regulate the interaction (Lautenschlager et al 2018). To understand how a-synuclein localizes to pre-synaptic boutons, we previously used fluorescence recovery after photobleaching (FRAP).…”