Role of the FtsA C terminus as a switch for polymerization and membrane association.

FtsA is a protein needed in many bacteria to construct a septum that divides one fully grown cell, producing two daughters. We show that the region located at the C-terminal end of the Streptococcus pneumoniae FtsA protein works as a switch triggered by ATP, a molecule that stores energy. This region contains an amphipathic helix that obstructs the assembly of FtsA into polymers in the cytoplasm. In the presence of ATP, the obstruction is removed by switching the position of the helix. The switch directs the helix to the membrane and simultaneously facilitates the polymerization of the protein. The accumulation of FtsA molecules at the membrane causes distortions, an effect produced also by proteins such as MinD, MreB, and SepF that also contain amphipathic helixes as membrane attachment devices. In the case of FtsA, these distortions may also facilitate the initial events that lead to the division of bacteria.