Localization of the Escherichia coli cell division protein FtsI (PBP3) to the division site and cell pole

Abstract

SummaryFtsI, also known as penicillin-binding protein 3, is a transpeptidase required for the synthesis of peptidoglycan in the division septum of the bacterium, Escherichia coli. FtsI has been estimated to be present at about 100 molecules per cell, well below the detection limit of immunoelectron microscopy. Here, we confirm the low abundance of FtsI and use immunofluorescence microscopy, a highly sensitive technique, to show that FtsI is localized to the division site during the later stages of cell growth. FtsI was also sometimes observed at the cell pole; polar localization was not anticipated and its significance is not known. We conclude (i) that immunofluorescence microscopy can be used to localize proteins whose abundance is as low as approximately 100 molecules per cell; and (ii) that spatial and temporal regulation of FtsI activity in septum formation is achieved, at least in part, by timed localization of the protein to the division site.

FtsK is an essential cell division protein that is localized to the septum and induced as part of the SOS response

“…However, the frequency at which FtsK is clearly localized at mid-cell was 70% (302 out of 428 cells counted), which is less than observed for FtsZ (96%; 445 out of 462) and FtsA (85%, 324 out of 378) but more than the 50% observed for FtsI (Wang and Lutkenhaus, 1998) and FtsN . Consistent with these frequencies, many cells without constrictions have FtsK localized to the septum, whereas localization of FtsI and FtsN is observed mostly in the cells with constrictions Weiss et al, 1997;Wang and Lutkenhaus, 1998). This suggests that localization of FtsK to the septum occurs later than FtsZ and FtsA but earlier than FtsI and FtsN.…”

“…The remaining cell division proteins are all membrane proteins and three of these, FtsN, FtsI and FtsW, have been localized to the septum Weiss et al, 1997;Wang and Lutkenhaus, 1998). The localization of FtsN has been examined in some detail .…”

Defining the rate-limiting processes of bacterial cytokinesis

“…To further investigate whether cell wall synthesis limits the progression of septum closure, we analyzed septum closure rates in a temperature-sensitive mutant strain, MCI23, in which the total cellular activity of the essential cell wall transpeptidase, FtsI (also known as PBP3), is reduced even at permissive temperatures, likely because of decreased thermostability of the protein (101). FtsI localizes to the septum at the onset of constriction (102,103) and exhibits stimulated transpeptidase activity in dividing cells compared with nondividing cells (104). If FtsI's PG synthesis activity, rather than Z-ring contraction, were a primary driver of septum closure, we would expect the lowered FtsI activity in the MCI23 strain to result in a reduced rate of septum closure.…”

Rapid β-lactam-induced lysis requires successful assembly of the cell division machinery

“…Bacterial cell division proceeds through the ordered assembly of a protein complex called the divisome (5), which includes a target of the ␤-lactams, FtsI (PBP3) (6)(7)(8). FtsI (PBP3) is the only essential penicillin-binding protein (PBP) required for division.…”