Title: 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.
Bio: Stephen Michnick received his B. Sc. and Ph. D. from the University of Toronto with Jeremy P. Carver and did postdoctoral training at the Department of Chemistry, Harvard University with Profs. Stuart Schreiber and Martin Karplus (Nobel Prize, Chemistry, 2013). He is presently a full professor in the Department of Biochemistry at Université de Montréal and Canada Research Chairs in cell architecture and Dynamics. He is an elected Fellow of the Royal Society of Canada and of the Royal Society of Chemistry of the UK. Prof. Michnick trained principally as a biophysical chemist, studying structures and binding of complex cell surface carbohydrate- and protein-protein interactions and mechanism of protein folding. At the heart of all of his work, protein chemistry remains central, but he has developed an eclectic and diverse research program aimed at studying the organization and dynamics of biochemical networks in living cells and how these networks compute cell-fate decisions. Dr. Michnick has received several honors, including in addition to Tier 1 and 2 Canada Research Chairs, a Burroughs-Wellcome New Investigator and Medical Research Council of Canada Scientist Awards and Canada Research Chairs in cell architecture and Dynamics. He is an elected Fellow of the Royal Society of Canada and of the Royal Society of Chemistry of the UK. Prof. Michnick manages an active and diverse research program and has received funding through MRC Canada, CIHR, NIH, NSERC, FRSQ, FRQNT, The Human Frontiers Science Program (HFSP), the Burroughs-Wellcome Fund, CFI, Canada Research Chairs, and a number of other agencies and private companies.