Protein condensate-induced bundling of cytoskeletal filaments

Fibers and filaments can assemble into materials through many different physical mechanisms. Cytoskeletal assemblies are canonically thought to be organized into different architectures through protein cross-linkers. Recently, it has been suggested that protein condensates could potentially induce assemble formation of cytoskeletal filaments. Here, we us fluorescence microscopy to show that protein condensates colocalize with actin filaments to form a coarsened network of bundles. We observe protein condensates adsorb to actin bundles and relax into barrel-shaped droplets, evocative of liquid drops on macroscopic fibers. These results provide experimental evidence of capillary-induced network formation and remodeling of biopolymer filaments. Research understanding mechanisms by which fibers and filaments arrange into different microstructures is crucial to the development of bioinspired and synthetic fibrous materials and understanding how cells regulate their mechanics.