Fig. 3. GTPase activity in FtsZ filaments promote spring compression and condensation.

Time-lapse acquisition of lipid tubes covered by a FtsZ-YFP-mts (N = 12) and b FtsZ-YFP-mts*[T108A] (N = 10). Both proteins promote helical deformations with the difference that GTPase activity induces compression (λ ~1.6 µm) of initially longer pitch (λ > 3 µm). FtsZ-YFP-mts is shown in green while lipids are shown in magenta (scale bar = 2 µm). c Tube deformation (arclength) in (a, b) against FtsZ-YFP-mts (green circles) and FtsZ-YFP-mts*[T108A] (gray circles) tube density, as function of time (Fig. 2SD), evidenced that GTPase activity caused greater tube deformation. d To rule out that compression was biased by the deflation state, we plotted tube diameter vs. mean pitch for FtsZ-YFP-mts (N = 12) (green) and FtsZ-YFP-mts*[T108A] (N = 10) (gray) in steady state. Despite of higher tube densities (arbitrary units) for FtsZ-YFP-mts*[T108A] as shown in (d—insert), the mean pitch for no GTPase case is longer at comparable tube diameters. e We observed two clear pitch states for FtsZ-YFP-mts (light green bars/green line) and FtsZ-YFP-mts*[T108A] (gray bars/magenta line) with a clear dominance of longer pitch for the mutant without GTPase activity. f Helical deformations can be understood by twisting an elastic rod subjected to constant force. We postulate that FtsZ has an intrinsic torsion that is enhanced by GTPase activity, driving further compression. Intrinsic FtsZ torsion rules long-pitch transformations (λ > 3 µm) while GTP enhances further torsion causing higher pitch states (λ < 2 µm).