Fig. 9: A phase-separated biomolecular PomY condensate nucleates polymerization of the tubulin homolog FtsZ to spatiotemporally regulate bacterial cell division.
a Schematic phase diagram for PomY phase separation dependent on crowding agent and protein concentration. b Schematic representation of PomY phase separation behavior. PomY by itself is homogeneously distributed below Csat, and phase separates above Csat (left panels). In the presence of PomX, PomY is enriched on the PomX scaffold below Csat and undergoes surface-assisted condensation on the PomX scaffold; above Csat, PomY condensates also form in the bulk and wet the PomX scaffold (right panels). c Model for the regulation of cell division by a biomolecular condensate in M. xanthus. I, a single PomX scaffold per cell is formed via high-affinity interactions among PomX molecules. II, PomY associates with the PomX scaffold via multivalent heterotypic interactions, thereby locally reaching a high concentration resulting in surface-assisted condensate formation on the PomX scaffold via homotypic PomYCC interactions. III, the PomX/PomY complex translocates on the nucleoid toward midcell via PomX/PomY-stimulated ATP hydrolysis by the DNA-bound PomZ ATPase. IV, at midcell, the PomY condensate enriches FtsZ locally via direct interaction. V, upon an unknown signal, FtsZ filaments emerge from the PomY condensates to form the Z-ring that recruits other proteins to execute cytokinesis. VI, during cytokinesis, the PomX scaffold undergoes fission and the PomY condensate disintegrates.
