An amphipathic helix facilitates direct membrane binding of Mycoplasma FtsZ

Abstract

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.