Effects of alpha-synuclein and synaptic vesicles on the material properties of synapsin condensates

Biomolecular condensates can recruit and segregate client molecules and are involved in various physiological processes. The material properties of a biomolecular condensate, as a mesoscale manifestation of intermolecular interactions, are crucial to its biological and pathological functions. Despite emerging reports about the changes in material properties of condensates in disease-related proteins, quantitative studies of the material properties of condensates are still rare. Here, we apply a calibration-free micropipette aspiration (MPA) assay to quantify the surface tension and viscosity of synapsin condensates. Furthermore, we investigated the effect of alpha-synuclein and synaptic vesicles (SVs) on the material properties of synapsin condensate. The results suggest that the recruitment of alpha-synuclein will increase the viscosity of synapsin condensate, and indicate the potential effects of SVs in mediating the material properties of synapsin condensates. Synapsin condensates are known to be essential for the formation of SV clusters. Therefore, our findings will help understand the regulation of SV dynamics during neurotransmission.