Molecular Mechanisms Underlying the Interaction between Synapsin, alpha-Synuclein and Synaptic Vesicles

• Applicant: Dr. Dragomir Milovanovic
• Subject Area: Biochemistry ; Molecular Biology and Physiology of Neurons and Glial Cells
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 465575936

Neurons communicate through tightly regulated secretion and uptake of messenger molecules referred to as neurotransmitters. These messenger molecules are packed into small lipid vesicles, so-called synaptic vesicles (SVs). On average, nerve terminals contain hundreds of SVs that are tightly clustered. Despite being clustered, SVs are highly mobile to assure the reliable release of neurotransmitters during sustained neuronal activity. Recently, we proposed that these clusters of SVs might represent an example of a liquid droplet at the synapse, such as a droplet of oil in water. Moreover, we have identified the synaptic-specific protein, synapsin 1, as responsible for the formation of these liquid droplets of lipid vesicles. The concept of liquid phase of synapsin and lipid vesicles provided a new framework to look at the organization of the synapse and raised important key question on how this process is regulated. The amino acid region of synapsin 1 responsible for its liquid condensation forms no specific secondary or tertiary structure. Other synaptic proteins contain similar regions, among which the most notable is alpha-synuclein, which is a small, disordered protein known for its involvement in the pathology of Parkinson’s disease. The main goal of this proposal is to characterize the molecular interplay between synapsin and alpha-synuclein and how their interaction affects the liquid phase of SVs. To achieve this goal, we will fuse biochemical reconstitution approaches, with the live-cell imaging of murine neurons. Specifically, the proposal contains two complementary approaches. The bottom-up approach includes cloning and purification of intrinsically disordered proteins, in vitro reconstitution of synapsin-driven SV condensates, and fluorescence-based assays. The top-down approach establishes a pipeline for live-cell imaging of SV clustering and the generation of mouse models with different concentrations of synapsin molecules. At the end of the proposal, we anticipate to decipher what features of protein sequence contribute to the architecture of SV condensates in the complex environment of the nerve terminal. The support of this research program will provide the opportunity for the initial groundwork to characterize how the interplay between synapsin and alpha-synuclein affects the physicochemical state of the synapse.

• DFG Programme: Research Grants