Summary Endocytosis underlies intra- and extracellular material trafficking in eukaryotes, and is essential to protein metabolism, intercellular signaling, membrane remodeling and other cell regulatory processes. Although endocytosis is usually driven by F-actin polymerization in yeast cells, membrane invagination can also occur through a yet unknown actin-independent mechanism when turgor pressure is relieved. Here, we demonstrate that membrane invagination can arise from liquid-liquid phase separation (demixing) of proteins with prion-like domains (PLD) from the cytosol. Demixing of these proteins results in the formation of a protein condensate, which, by virtue of its composition and viscoelastic properties, binds to and deforms plasma membrane and cytosol. Demonstration that phase separated condensates can perform mechanical work expands the repertoire of known functions of protein condensates to include the ability to do work at soft interfaces such as between the condensate and the membrane. Similar mechanisms may govern or contribute to other membrane shaping, invagination and budding processes that are involved in cellular material uptake, secretion, and cell shape remodeling.
