The Escherichia coli cell division protein FtsW is required to recruit its cognate transpeptidase, FtsI (PBP3), to the division site - PubMed (original) (raw)

The Escherichia coli cell division protein FtsW is required to recruit its cognate transpeptidase, FtsI (PBP3), to the division site

Keri L N Mercer et al. J Bacteriol. 2002 Feb.

Abstract

The bacterial cell division protein FtsW has been suggested to perform two functions: stabilize the FtsZ cytokinetic ring, and facilitate septal peptidoglycan synthesis by the transpeptidase FtsI (penicillin-binding protein 3). We show here that depleting Escherichia coli cells of FtsW had little effect on the abundance of FtsZ rings but abrogated recruitment of FtsI to potential division sites. Analysis of FtsW localization confirmed and extended these results; septal localization of FtsW required FtsZ, FtsA, FtsQ, and FtsL but not FtsI. Thus, FtsW is a late recruit to the division site and is essential for subsequent recruitment of its cognate transpeptidase FtsI but not for stabilization of FtsZ rings. We suggest that a primary function of FtsW homologues--which are found in almost all bacteria and appear to work in conjunction with dedicated transpeptidases involved in division, elongation, or sporulation--is to recruit their cognate transpeptidases to the correct subcellular location.

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Figures

FIG. 1.

FIG. 1.

Recruitment of division proteins to the septal ring of E. coli. The first event is polymerization of FtsZ into the Z-ring. The other proteins localize in the order indicated. For a recent review, see reference . The position of FtsK is from reference . The position of FtsW is from this work.

FIG. 2.

FIG. 2.

Localization of division proteins in an FtsW depletion background. Strains expressing the indicated GFP fusion were grown in the presence of arabinose or glucose to induce or prevent expression of ftsW, respectively. Cells were fixed and then mixed prior to spreading on slides for microscopy. The short (arabinose-grown) cells often display septal localization of the target division protein and serve as internal controls for microscopy and subsequent image processing. The strains shown are EC856, EC892, EC904, EC860, EC881, and EC861.

FIG. 3.

FIG. 3.

Steady-state levels of GFP-FtsW fusion protein as determined by Western blotting with an anti-GFP antibody. The positions of molecular mass standards (in kilodaltons) and the positions of GFP-FtsW and GFP-FtsI are indicated. Strain EC791 (P209-gfp-ftsW) was grown with 0 mM IPTG (lane 1) or 1 mM IPTG (lane 2). Strain EC436 (P207-gfp-ftsI) was grown with 2.5 μM IPTG (lane 3), which results in production of ≈200 molecules of GFP-FtsI per cell (44). Promoter P209 is much weaker than P207 (44). Chemiluminescence signal was recorded on film, which was then scanned to prepare this figure. In addition, chemiluminescence signal from bands corresponding to the GFP fusion proteins was quantified directly on a Typhoon 8600 imager. The values were 480 for GFP-FtsW uninduced, 3,300 for GFP-FtsW induced, and 3,500 for GFP-FtsI (arbitrary units, corrected for background).

FIG. 4.

FIG. 4.

Localization of GFP-FtsW during exponential growth. (A) GFP imaged in a field of cells of strain EC791. (B) Quantitation of the fluorescence in cells that do (a) and do not (b) display septal localization of GFP-FtsW. Transects run lengthwise through the cells indicated in panel A, starting about 1 μm before (lower left) and extending about 1 μm beyond (upper right) each cell. (C) Size distribution of cells that display septal localization of GFP-FtsW. A total of 696 cells were measured and scored for the presence (black bar) or absence (hatched bar) of a fluorescent band extending across the midcell.

FIG. 5.

FIG. 5.

Dependency of GFP-FtsW localization on other Fts proteins. In each case the indicated fts mutant was grown in parallel under permissive and nonpermissive conditions (60 min for temperature-sensitive mutants). Cells were fixed and then mixed prior to spreading on slides for microscopy. The short (permissive condition) cells often display septal localization of GFP-FtsW and serve as internal controls for microscopy and subsequent image processing. The strains shown are EC788, EC787, EC799, EC798, and EC829.

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