Single-vesicle imaging quantifies calcium's regulation of nanoscale vesicle clustering mediated by α-synuclein

Docosahexaenoic acid promotes vesicle clustering mediated by alpha-Synuclein via electrostatic interaction

α-Synuclein (α-Syn) is an intrinsically disordered protein whose aggregation is associated with Parkinson's disease, dementia, and other neurodegenerative diseases known as synucleinopathies. However, the functional role of α-Syn is still unclear, although it has been shown to be involved in the regulation of neurotransmitter release via the interaction with synaptic vesicles (SVs), vesicle clustering, and SNARE complex assembly. Fatty acids have significant occupancy in synaptic vesicles; and recent studies suggest the interaction of fatty acids with α-Syn affect the formation of (pathological) aggregates, but it is less clear how fatty acids affects the functional role of α-Syn including α-Syn-membrane interactions, in particular with (SV-like) vesicles. Here, we report the concentration dependent effect of docosahexaenoic acid (DHA) in synaptic-like vesicle clustering via α-Syn interaction. Through molecular dynamics simulation, we revealed that DHA promoted vesicle clustering is due to the electrostatic interaction between DHA in the membrane and the N-terminal region of α-Syn. Moreover, this increased electrostatic interaction arises from a change in the macroscopic properties of the protein-membrane interface induced by (preferential solvation of) DHA. Our results provide insight as to how DHA regulates vesicle clustering mediated by α-Syn and may further be useful to understand its physiological as well as pathological role. Description: In physiological environments, α-Synuclein (α-Syn) localizes at nerve termini and synaptic vesicles and interacts with anionic phospholipid membranes to promote vesicle clustering. Docosahexaenoic acid (DHA) increases binding affinity between α-Syn and lipid membranes by increasing electrostatic interaction energy through modulating the local and global membrane environment and conformational properties of α-Syn.

The function of VAMP2 in mediating membrane fusion: An overview

Vesicle-associated membrane protein 2 (VAMP2, also known as synaptobrevin-2), encoded by VAMP2 in humans, is a key component of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex. VAMP2 combined with syntaxin-1A (SYX-1A) and synaptosome-associated protein 25 (SNAP-25) produces a force that induces the formation of fusion pores, thereby mediating the fusion of synaptic vesicles and the release of neurotransmitters. VAMP2 is largely unstructured in the absence of interaction partners. Upon interaction with other SNAREs, the structure of VAMP2 stabilizes, resulting in the formation of four structural domains. In this review, we highlight the current knowledge of the roles of the VAMP2 domains and the interaction between VAMP2 and various fusion-related proteins in the presynaptic cytoplasm during the fusion process. Our summary will contribute to a better understanding of the roles of the VAMP2 protein in membrane fusion.

"Janus-Faced" α-Synuclein: Role in Parkinson's Disease

Parkinson's disease (PD) is a pathological condition characterized by the aggregation and the resultant presence of intraneuronal inclusions termed Lewy bodies (LBs) and Lewy neurites which are mainly composed of fibrillar α-synuclein (α-syn) protein. Pathogenic aggregation of α-syn is identified as the major cause of LBs deposition. Several mutations in α-syn showing varied aggregation kinetics in comparison to the wild type (WT) α-syn are reported in PD (A30P, E46K, H 50Q, G51D, A53E, and A53T). Also, the cell-to-cell spread of pathological α-syn plays a significant role in PD development. Interestingly, it has also been suggested that the pathology of PD may begin in the gastrointestinal tract and spread via the vagus nerve (VN) to brain proposing the gut-brain axis of α-syn pathology in PD. Despite multiple efforts, the behavior and functions of this protein in normal and pathological states (specifically in PD) is far from understood. Furthermore, the etiological factors responsible for triggering aggregation of this protein remain elusive. This review is an attempt to collate and present latest information on α-syn in relation to its structure, biochemistry and biophysics of aggregation in PD. Current advances in therapeutic efforts toward clearing the pathogenic α-syn via autophagy/lysosomal flux are also reviewed and reported.

Membrane packing defects in synaptic vesicles recruit complexin and synuclein

Complexin-1 (Cpx) and α-synuclein (α-Syn) are involved in neurotransmitter release through an interaction with synaptic vesicles (SVs). Recent studies demonstrated that Cpx and α-Syn preferentially associate with highly curved membranes, like SVs, to correctly position them for fusion. Here, based on recent experimental results, to further propose a possible explanation for this mechanism, we performed in silico simulations probing interactions between Cpx or α-Syn and membranes of varying curvature. We found that the preferential association is attributed to smaller, curved membranes containing more packing defects that expose hydrophobic acyl tails, which may favorably interact with hydrophobic residues of Cpx and α-Syn. The number of membrane defects is proportional to the curvature and the size can be regulated by cholesterol.