Cell Cycle-Dependent Recruitment of FtsN to the Divisome in Escherichia coli.

Cell division in Escherichia coli starts with the formation of an FtsZ protofilament network at midcell, the Z ring. However, only after a considerable lag period does the cell start to form a midcell constriction. The onset of constriction depends upon the arrival of so-called late divisome proteins, among which, FtsN is the last essential one.

FtsA acts through FtsW to promote cell wall synthesis during cell division in .

In , FtsQLB is required to recruit the essential septal peptidoglycan (sPG) synthase FtsWI to FtsA, which tethers FtsZ filaments to the membrane. The arrival of FtsN switches FtsQLB in the periplasm and FtsA in the cytoplasm from a recruitment role to active forms that synergize to activate FtsWI. Genetic evidence indicates that the active form of FtsQLB has an altered conformation with an exposed domain of FtsL that acts on FtsI to activate FtsW.

Roles of ATP Hydrolysis by FtsEX and Interaction with FtsA in Regulation of Septal Peptidoglycan Synthesis and Hydrolysis.

In , FtsEX coordinates peptidoglycan (PG) synthesis and hydrolysis at the septum. It acts on FtsA in the cytoplasm to promote recruitment of septal PG synthetases and recruits EnvC, an activator of septal PG hydrolases, in the periplasm. Following recruitment, ATP hydrolysis by FtsEX is thought to regulate both PG synthesis and hydrolysis, but how it does this is not well understood.

Roles of FtsEX in cell division.

FtsEX is a member of a small subclass of ABC transporters that uses mechano-transmission to perform work in the periplasm. FtsEX controls periplasmic peptidoglycan (PG) hydrolase activities in many Gram negative and positive organisms to ensure the safe separation of daughter cells during division. In these organisms FtsEX localizes to the Z ring and uses its ATPase activity to regulate its periplasmic effectors.

How FtsEX localizes to the Z ring and interacts with FtsA to regulate cell division.

In Escherichia coli, FtsEX, a member of the ABC transporter superfamily, is involved in regulating the assembly and activation of the divisome to couple cell wall synthesis to cell wall hydrolysis at the septum. Genetic studies indicate FtsEX acts on FtsA to begin the recruitment of the downstream division proteins but blocks septal PG synthesis until a signal is received that divisome assembly is complete. However, the details of how FtsEX localizes to the Z ring and how it interacts with FtsA are not clear.

FtsZ filaments have the opposite kinetic polarity of microtubules.

FtsZ is the ancestral homolog of tubulin and assembles into the Z ring that organizes the division machinery to drive cell division in most bacteria. In contrast to tubulin that assembles into 13 stranded microtubules that undergo dynamic instability, FtsZ assembles into single-stranded filaments that treadmill to distribute the peptidoglycan synthetic machinery at the septum. Here, using longitudinal interface mutants of FtsZ, we demonstrate that the kinetic polarity of FtsZ filaments is opposite to that of microtubules.

Disruption of divisome assembly rescued by FtsN-FtsA interaction in .

Cell division requires the assembly of a protein complex called the divisome. The divisome assembles in a hierarchical manner, with FtsA functioning as a hub to connect the Z-ring with the rest of the divisome and FtsN arriving last to activate the machine to synthesize peptidoglycan. FtsEX arrives as the Z-ring forms and acts on FtsA to initiate recruitment of the other divisome components.

FtsEX acts on FtsA to regulate divisome assembly and activity.

Bacterial cell division is driven by the divisome, a ring-shaped protein complex organized by the bacterial tubulin homolog FtsZ. Although most of the division proteins in Escherichia coli have been identified, how they assemble into the divisome and synthesize the septum remains poorly understood. Recent studies suggest that the bacterial actin homolog FtsA plays a critical role in divisome assembly and acts synergistically with the FtsQLB complex to regulate the activity of the divisome.

The bypass of ZipA by overexpression of FtsN requires a previously unknown conserved FtsN motif essential for FtsA-FtsN interaction supporting a model in which FtsA monomers recruit late cell division proteins to the Z ring.

Assembly of the divisome in Escherichia coli occurs in two temporally distinct steps. First, FtsZ filaments attached to the membrane through interaction with FtsA and ZipA coalesce into a Z ring at midcell. Then, additional proteins are recruited to the Z ring in a hierarchical manner to form a complete divisome, activated by the arrival of FtsN.

Bacterial cytokinesis: From Z ring to divisome.

Ancestral homologues of the major eukaryotic cytoskeletal families, tubulin and actin, play critical roles in cytokinesis of bacterial cells. FtsZ is the ancestral homologue of tubulin and assembles into the Z ring that determines the division plane. FtsA, a member of the actin family, is involved in coordinating cell wall synthesis during cytokinesis.

FtsA mutants impaired for self-interaction bypass ZipA suggesting a model in which FtsA's self-interaction competes with its ability to recruit downstream division proteins.

Z-ring assembly requires polymers of the tubulin homologue FtsZ to be tethered to the membrane. Although either ZipA or FtsA is sufficient to do this, both of these are required for recruitment of downstream proteins to form a functional cytokinetic ring. Gain of function mutations in ftsA, such as ftsA* (ftsA-R286W), bypass the requirement for ZipA suggesting that this atypical, well-conserved, actin homologue has a more critical role in Z-ring function.

Cross-linking FtsZ polymers into coherent Z rings.

A key event in bacterial cytokinesis is the formation of the Z ring, which serves as a mechanical scaffold that recruits other cytokinetic proteins to establish functional divisomes. This scaffolding function of Z rings is essential throughout cytokinesis, but the underlying molecular interactions are poorly understood. Here we report that a widely conserved FtsZ binding protein, ZapA, has cytological, biochemical and biophysical properties that argue for the importance of cross-linking interactions between FtsZ polymers in the coherence of Z rings.

Overview of cell shape: cytoskeletons shape bacterial cells.

An evolving hypothesis is that bacterial cell shape is determined by cytoskeletal elements that localize peptidoglycan synthetic machineries. In most bacteria FtsZ assembles into the Z ring which recruits the machinery necessary for cytokinesis. Most rod shaped cells require MreB which assembles into cables that run between the poles of the cell and distribute various components of peptidoglycan metabolism along the cell length.

Identification of a region of FtsA required for interaction with FtsZ.

The assembly of the Z ring is the earliest step in bacterial cell division. In Escherichia coli this assembly requires either FtsA or ZipA which bind to a conserved, C-terminal 17 amino acid motif in FtsZ and to the membrane. The FtsZ-ZipA interaction is well characterized; however, nothing is known about the region of FtsA involved in the interaction with FtsZ even though the FtsA-FtsZ interaction is nearly ubiquitous in Eubacteria.

Tethering the Z ring to the membrane through a conserved membrane targeting sequence in FtsA.

The cytokinetic Z ring is required for bacterial cell division. It consists of polymers of FtsZ, the bacterial ancestor of eukaryotic tubulin, linked to the cytoplasmic membrane. Formation of a Z ring in Escherichia coli occurs as long as one of two proteins, ZipA or FtsA, is present.

Unique and overlapping roles for ZipA and FtsA in septal ring assembly in Escherichia coli.

ZipA and FtsA are essential division proteins in Escherichia coli that are recruited to the division site by interaction with FtsZ. Utilizing a newly isolated temperature-sensitive mutation in zipA we have more fully characterized the role of ZipA. We confirmed that ZipA is not required for Z ring formation; however, we found that ZipA, like FtsA, is required for recruitment of FtsK and therefore all downstream division proteins.