Self-organisation of mortal filaments: the role of FtsZ treadmilling in bacterial division ring formation

Protein filaments in the cell commonly treadmill - they grow on one end while shrinking on the other, driven by energy consumption. Treadmilling filaments appear to be moving, even though individual proteins remain static. Here, we investigate the role of treadmilling, implemented as dynamic turnover, in the collective filament self-organisation. On the example of the bacterial FtsZ protein, a highly conserved tubulin homologue, we show, in computer simulations and in vitro experiments, that treadmilling drives filament nematic ordering by dissolving misaligned filaments. We demonstrate that ordering via local dissolution allows the system to quickly respond to chemical and geometrical biases in the cell, and is necessary for the formation of the FtsZ ring required for bacterial cell division in living Bacillus subtilis cells. We finally use simulations to quantitatively explain the characteristic dynamics of FtsZ ring formation in vivo. Beyond FtsZ and other cytoskeletal filaments, our study identifies a novel mechanism for nematic ordering via constant birth and death of energy-consuming filaments.