Fig. 8. A model for the influence of ZapA and its role for Z-ring maturation.

Binding of ZapA aligns treadmilling FtsZ filaments (1), which in turn facilitates its binding, giving rise to cooperativity (2). At saturation, four molecules of FtsZ bind to one tetramer of ZapA (1:1 monomer ratio, [FtsZ] = [ZapA]) in parallel increasing the bundle width, persistence and alignment of FtsZ filaments (3). Treadmilling is not affected due to the transient binding of ZapA. Together, ZapA leads to a shift from a network of less ordered and highly dynamic FtsZ filaments (4) into a more well-defined track, acting as an additional fine-tune mechanism for a proper Z-ring alignment (5) without compromising treadmilling dynamics.