A Predicted ABC Transporter, FtsEX, Is Needed for Cell Division in Escherichia coli

Abstract

FtsE and FtsX have homology to the ABC transporter superfamily of proteins and appear to be widely conserved among bacteria. Early work implicated FtsEX in cell division in Escherichia coli, but this was subsequently challenged, in part because the division defects in ftsEX mutants are often salt remedial. Strain RG60 has an ftsE::kan null mutation that is polar onto ftsX. RG60 is mildly filamentous when grown in standard Luria-Bertani medium (LB), which contains 1% NaCl, but upon shift to LB with no NaCl growth and division stop. We found that FtsN localizes to potential division sites, albeit poorly, in RG60 grown in LB with 1% NaCl. We also found that in wild-type E. coli both FtsE and FtsX localize to the division site. Localization of FtsX was studied in detail and appeared to require FtsZ, FtsA, and ZipA, but not the downstream division proteins FtsK, FtsQ, FtsL, and FtsI. Consistent with this, in media lacking salt, FtsA and ZipA localized independently of FtsEX, but the downstream proteins did not. Finally, in the absence of salt, cells depleted of FtsEX stopped dividing before any change in growth rate (mass increase) was apparent. We conclude that FtsEX participates directly in the process of cell division and is important for assembly or stability of the septal ring, especially in salt-free media.In Escherichia coli, the division septum forms via the coordinated inward growth of all three layers of the cell envelopethe cytoplasmic membrane, the peptidoglycan wall, and the outer membrane. To date, about a dozen E. coli genes are known to be specifically required for septation (3, 11). These genes share two important properties: (i) loss of function mutations result in the formation of long, aseptate filaments with regularly spaced nucleoids (the fts, or filamentation temperature-sensitive phenotype), and (ii) the proteins encoded by these genes localize to the division site. Because cell division genes are generally essential and because lesions in many housekeeping genes can affect cell division indirectly, there have not been any exhaustive screens for division mutants. Thus, it seems likely that more division genes remain to be described.A number of mutant hunts, starting with the pioneering work of Hirota and coworkers in the 1960s, suggested that there is an important cell division gene located at about 76 min on the E. coli chromosome (30). This locus was originally designated ftsE. One interesting property of ftsE mutants is that many are salt remedial, meaning that viability is restored by inclusion of NaCl in the growth medium. The amount of salt required for rescue is strain dependent, but generally in the range of 0.5%. Studies by Salmond and colleagues in the 1980s revealed that "ftsE" comprised two genes, which were then designated ftsE and ftsX (13). Moreover, the sequence of these genes revealed clear homology to ABC transporters; FtsE is the ATP-binding cassette (ABC) component, while FtsX is the membrane component. ABC transporters use energy from ATP to transport a wide variety of sub...

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“…As expected for an integrated system, FtsE fails to localize to the divisome in the absence of FtsX (13). FtsEX shows homology to ABC transporters (14,15). FtsE, a predicted ATP binding cassette, requires wild-type Walker motifs for function, implicating ATP turnover in signaling (11).…”

Targeting cell division: Small-molecule inhibitors of FtsZ GTPase perturb cytokinetic ring assembly and induce bacterial lethality

“…The earliest known step in bacterial cytokinesis is the assembly of the essential division protein FtsZ into the contractile Z ring on the inner face of the cytoplasmic membrane at the site of division (1)(2)(3). Another 12 proteins in Escherichia coli then congregate at the Z ring in a sequentially dependent pathway, causing assembly of the septal ring that guides circumferential septum synthesis (2)(3)(4)(5). The septal ring constricts in concert with septal progression, culminating in complete disassembly once the septum matures.…”

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