ZapA tetramerization is required for midcell localization and ZapB interaction in Escherichia coli

Bacterial cell division is guided by FtsZ treadmilling precisely at midcell. FtsZ itself is regulated by FtsZ associated proteins (Zaps) that couple it to different cellular processes. ZapA is known to enhance FtsZ bundling but also forms the synchronizing link with chromosome segregation through ZapB and bound MatP. ZapA exists as dimers and tetramers in the cell. Using the ZapA mutant that only forms dimers, this paper investigates the effects of ZapA multimerization state on its interaction partners and cell division. By employing (fluorescence) microscopy and Förster Resonance Energy Transfer it is shown that; dimeric ZapA is unable to complement a deletion strain and localizes diffusely through the cell but still interacts with FtsZ that is not part of the cell division machinery. Dimeric ZapA is unable to recruit ZapB, which localizes in its presence unipolarly in the cell. Interestingly, the localization profiles of the chromosome and unipolar ZapB anticorrelate. The work presented here confirms previously reported effects of ZapA multimerization and further places it in a broader context by revealing the strong implications for ZapB localization and linkage.