Abstract
FtsZ, the primary protein of the bacterial Z ring guiding cell division, has been recently shown to engage in intriguing treadmilling dynamics along the circumference of the division plane. When coreconstituted in vitro with FtsA, one of its natural membrane anchors, on flat supported membranes, these proteins assemble into dynamic chiral vortices compatible with treadmilling of curved polar filaments. Replacing FtsA by a membrane-targeting sequence (mts) to FtsZ, we have discovered conditions for the formation of dynamic rings, showing that the phenomenon is intrinsic to FtsZ. Ring formation is only observed for a narrow range of protein concentrations at the bilayer, which is highly modulated by free Mg2+ and depends upon guanosine triphosphate (GTP) hydrolysis. Interestingly, the direction of rotation can be reversed by switching the mts from the C-terminus to the N-terminus of the protein, implying that the filament attachment must have a perpendicular component to both curvature and polarity. Remarkably, this chirality switch concurs with previously shown inward or outward membrane deformations by the respective FtsZ mutants. Our results lead us to suggest an intrinsic helicity of FtsZ filaments with more than one direction of curvature, supporting earlier hypotheses and experimental evidence.
Highlights
For the fundamental task of cell and organelle division, life has evolved various strategies, many of which are based on ringlike contractile structures assembling from within a compartment to induce binary fission
We found that dynamic ring formation is an intrinsic feature of FtsZ without the need of any other protein
We have found that FtsZ-yellow fluorescent protein (YFP)-mts under assembly-promoting conditions (4 mM guanosine triphosphate (GTP), 5 mM Mg2+) formed filaments on supported lipid bilayers (SLBs), which self-organize with time into dynamic ringlike structures (S1 Movie)
Summary
For the fundamental task of cell and organelle division, life has evolved various strategies, many of which are based on ringlike contractile structures assembling from within a compartment to induce binary fission. Guanosine triphosphate (GTP)-dependent structural changes of FtsZ monomers and membrane-attached filaments toward greater curvatures have been proposed, but evidence has been lacking for how a continuously shrinking membrane orifice could be engineered from them. This is mainly due to the fact that the closure dynamics of Z rings could be observed in vivo [7,8], there is yet no direct proof that purified Z rings may actively proceed to closure through all stages of increasing curvature [3,9]
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