An amphipathic helix facilitates direct membrane binding of Mycoplasma FtsZ

Cell division in bacteria is initiated by constriction of the Z-ring comprising two essential proteins FtsZ and FtsA. Despite our knowledge about the crucial function of the Z-ring in bacterial division, the precise roles and mechanism of how FtsZ and FtsA drive cell constriction remain elusive. FtsZ/FtsA in wall-less bacteria like mycoplasmas is an ideal model system for obtaining mechanistic insights into Z-ring constriction in the absence of cell wall machinery. In this study, we have analyzed FtsZ and FtsA sequences of 113 mycoplasma species and compared with the corresponding protein sequences in cell-walled bacteria. We report a phylogenetically distinct group of 12 species that possess FtsZs without the canonical FtsA interacting conserved C-terminal peptide (CCTP) motif. Interestingly, these FtsZs contain a putative membrane-binding amphipathic helix as an N-terminal or C-terminal extension to the globular FtsZ domain. As a proof-of-concept, we experimentally show that the proposed C-terminal amphipathic helix in M. genitalium FtsZ binds liposomes in vitro as well as localizes to E. coli membrane in vivo. Additionally, we identify a putative cholesterol recognition motif within the C-terminal amphipathic helix region of M. genitalium FtsZ. Our study catalogues the functional variations of membrane attachment by the FtsZ and FtsA system in cell wall-less mycoplasmas and provides a new perspective to study novel functions of FtsZ/A system in cell division. ImportanceZ-ring and peptidoglycan synthesis machinery both play crucial roles in bacterial cell division. Currently, our knowledge about how FtsZ and FtsA, the two primary components of the Z-ring, function, is limited to cell-walled bacteria where ring constriction is coupled to peptidoglycan synthesis. Cell wall-less bacterial FtsZ/A system is an excellent model to study the mechanism of Z-ring constriction in the absence of cell wall synthesis machinery. Here, we analysed FtsZ protein sequences across mycoplasma species and identified their characteristic sequence features. Our study reveals a novel group of FtsZs from mycoplasma with an inherent membrane binding and probable cholesterol sensing amphipathic motif, which serves as a new paradigm to explore fundamental roles of FtsZ and FtsA in Z-ring constriction during bacterial division.