Last but not least: new insights into how FtsN triggers constriction during Escherichia coli cell division.

The arrival of FtsN at the division site triggers synthesis of septal peptidoglycan and constriction of the cell envelope. New findings are changing our view of how this happens. Binding of FtsN's cytoplasmic domain to a protein named FtsA recruits a small amount of FtsN to the division site earlier than previously recognized. The ability of FtsA to interact with FtsN is regulated by the ZipA protein. The FtsN-FtsA interaction pushes FtsA into an 'on' conformation that activates the machinery for peptidoglycan synthesis. In addition, a small region of FtsN's periplasmic domain appears to interact with the FtsQLB complex, pushing it into an 'on' state that also triggers synthesis of peptidoglycan. Thus, FtsN allosterically activates peptidoglycan synthesis by two pathways, one in the cytoplasm and involving FtsA, and the other in the periplasm and involving FtsQLB.