The flagellar-specific transcription factor, σ²⁸, is the Type III secretion chaperone for the flagellar-specific anti-σ²⁸ factor FlgM

Abstract

The bacterial flagellum is a self-assembling macromolecular machine anchored in the bacterial membrane that allows bacteria to move through liquid environments or crawl along surfaces (Macnab 1992). Flagellar assembly and function is a complex process, which in Salmonella typhimurium involves over 60 genes (Frye et al. 2006). The construction of individual flagella requires an ordered assembly pathway (Macnab 1992). The assembly process involves the secretion of individual subunits through the hollow core of the growing flagellum where they assemble at the tip of the structure. In addition, multi-flagellated bacteria can have individual flagella in the same cell at different stages of assembly (Bardy et al. 2003). Consequently, the assembly process is tightly regulated at the levels of substrate selection by the associated secretion apparatus and coupled gene regulation. This paper reports an unexpected discovery related to the current understanding of how a cell regulates flagellar gene expression in response to intermediate stages of flagellar assembly. A flagellar-specific transcription factor, 28, plays a dual role as both a regulator of gene expression and a facilitator of flagellar-specific Type III secretion.The bacterial flagellum consists of three major substructures: (1) the basal body, which acts as motor anchoring the flagellum within the cell membranes; (2) the hook, which acts as a flexible, universal joint between the basal body; and (3) the long external filament, which acts as a propeller when rotated (Berg and Anderson 1973;Macnab 1999). Self-assembly of a flagellum begins at the inner membrane and proceeds out of the cell with construction of the basal structure. A flagellar-specific Type III secretion (T3S) apparatus is assembled within the cytoplasmic membrane at the base of the basal structure (Aldridge and Hughes 2002). Individual structural subunits are then secreted from the cytoplasm into the growing flagellum by the flagellar T3S system. Efficient flagellar assembly requires that the T3S apparatus distinguish between different secretion substrates at different stages of assembly. Recent studies have shown that there is a multi-layered regulatory network in place that couples temporal expression and delivery of flagellar

Biochemical characterization of the enterotoxigenic Escherichia coli LeoA protein

“…We identified this protein by mass spectrometry as FliC. FliC is the major component of the bacterial flagellum (Aldridge et al, 2006), which has a proven role in E. coli motility (Gomez-Gomez et al, 2007), ) in the indicated plate octants: 1, sepD-pBT sepLpTRG; 2, ompA-pBT leoA-pTRG; 3, ompA-pBT leoADG-pTRG; 4, ompA-pTRG leoA-pBT; 5, ompA-pTRG leoADG-pBT; 6, leoA-pBT leoA-pTRG; 7, leoADG-pBT leoADG-pTRG; 8, ompA-pBT ompA-pTRG. host cell adherence (Giron et al, 2002;Wright et al, 2005), invasion (Parthasarathy et al, 2007) and virulence (Giron et al, 2002;Parthasarathy et al, 2007).…”

Genetically Programmable Pathogen Sense and Destroy

“…For example it was shown that certain mutation in HlyA protein caused increased secretion from type one secretion system [169]. Similarly, efficiency of FlgM secretion was improved in fliS and fliT mutants [132]. However, a deletion of FliC, D, S, T genes did not result in increase of FlgM-CoPy secretion as shown in Figure 50.…”

“…Secretion can be improved in future by testing this hypothesis and resolving it as shown in [118]. Secretion efficiency can be further increased by modifying the flagellar machinery involved in exporting native FlgM [128,132,135,[153][154][155][156][157][158]. There are several factors which affect the expression and secretion efficiency of recombinant proteins from E. coli.…”

“…Therefore, I employed flagellar system to secrete CoPy. FlgM is a Sigma factor used in the regulation of the bacterial flagellar machinery and is naturally secreted into the extracellular space [126,132,136,152]. Hence…”

Mathematical model of flagella gene expression dynamics in Salmonella enterica serovar typhimurium

“…FlgM is assumed to be only exported when bound to FliA. Absence of FliA, reduces secretion of FlgM significantly, and has been ignored in the model (Aldridge et al 2006). Similarly, it has been assumed in the model that FliD is only secreted from the cell when bound with its chaperone FliT.…”