Cell division in Escherichia coli: Role of FtsL domains in septal localization, function, and oligomerization

In Escherichia coli, nine essential cell division proteins are known to loc alize to the division septum. FtsL is a 13-kDa bitopic membrane protein wit h a short cytoplasmic N-terminal domain, a membrane-spanning segment, and a periplasmic domain that has a repeated heptad motif characteristic of leuc ine zippers. Here, we identify the requirements for FtsL septal localizatio n and function. We used green fluorescent protein fusions to FtsL proteins where domains of FtsL had been exchanged with analogous domains from either its Haemophilus influenzae homologue or the unrelated MalF protein to show that both the membrane-spanning segment and the periplasmic domain of FtsL are required for localization to the division site. Mutagenesis of the per iplasmic heptad repeat motif severely impaired both localization and functi on as well as the ability of FtsL to drive the formation of sodium dodecyl sulfate-resistant multimers in vitro. These results are consistent with the predicted propensity of the FtsL periplasmic domain to adopt a coiled-coil ed structure. This coiled-coil motif is conserved in all gram-negative and gram-positive FtsL homologues identified so far. Our data suggest that most of the FtsL molecule is a helical coiled coil involved in FtsL multimeriza tion.