Synthetic Membraneless Droplets for Synaptic-Like Clustering of Lipid Vesicles

In eukaryotic cells, the membraneless organelles (MLOs) formed via liquid-liquid phase separation (LLPS) are found to interact intimately with membranous organelles (MOs). One major mode is the clustering of MOs by MLOs, such as the formation of clusters of synaptic vesicles at nerve terminals mediated by the synapsin-rich MLOs. Aqueous droplets, including complex coacervates and aqueous two-phase systems, have been plausible MLO-mimics to emulate or elucidate biological processes. However, neither of them can cluster lipid vesicles (LVs) like MLOs. In this work, we develop a synthetic droplet assembled from a combination of two different interactions underlying the formation of these two droplets, namely, associative and segregative interactions, which we call segregative-associative (SA) droplets. The SA droplets cluster and disperse LVs recapitulating the key functional features of synapsin condensates, which can be attributed to the weak electrostatic interaction environment provided by SA droplets. This work suggests LLPS with combined segregative and associative interactions as a possible route for synaptic clustering of lipid vesicles and highlights SA droplets as plausible MLO-mimics and models for studying and mimicking related cellular dynamics. We demonstrate a new aqueous droplet as mimic of membraneless organelles (MLOs), which we call segregative-associative (SA) droplets, apart from the widely known complex coacervates and neutral polymer-based aqueous two-phase systems. The SA droplet exhibits MLO-mimicking complex phase behaviors and can cluster charged lipid vesicles like MLOs at synapse, which has been hitherto unachievable for most current MLO-mimics.+image

Automated summary

In this study, a synthetic droplet called segregative-associative (SA) droplets is developed to mimic membraneless organelles (MLOs) in cells. These SA droplets exhibit complex phase behaviors similar to MLOs and can cluster lipid vesicles like synapsin condensates.