Preparation and preliminary X-ray diffraction analysis of crystals of bacterial flagellar sigma factor sigma 28 in complex with the sigma 28-binding region of its antisigma factor, FlgM

Functional characterization of FlgM in the regulation of flagellar synthesis and motility in Yersinia pseudotuberculosis

We describe here the functional characterization of the flgM gene in Yersinia pseudotuberculosis. Direct interaction of FlgM with the alternative sigma factor σ 28 (FliA) was first confirmed. A conserved region in the C-terminus of FlgM was found which included the σ 28 binding domain. By site-directed mutagenesis, bacterial two-hybrid analysis and Western blotting, the primary FlgM binding sites with σ 28 were shown to be Ile85, Ala86 and Leu89. A role for FlgM in swimming motility was demonstrated by inactivation of flgM and subsequent complementation in trans. Transcriptional fusion analyses showed differential gene expression of flhDC, fliA, flgM and fliC in the fliA and flgM mutants compared with the wild-type. flhDC expression was not influenced by σ 28 or FlgM while fliA expression was abolished in the fliA mutant and considerably reduced in the flgM mutant when compared to the wild-type, indicating that both FliA and FlgM can activate fliA transcription. Conversely, flgM transcription was higher in the fliA mutant when compared to the wild-type, suggesting that flgM transcription was repressed by σ 28. Interestingly, fliC expression was markedly increased in the flgM mutant, suggesting a negative regulatory role for FlgM in fliC expression. The transcription of other σ-dependent genes (cheW, flgD, flaA, csrA and fliZ) was also examined in fliA and flgM mutant backgrounds and this revealed that other σ-factors apart from σ 28 may be involved in flagellar biogenesis in Y. pseudotuberculosis. Taking together the motility phenotypes and effects of flgM mutation on the regulation of these key motility genes, we propose that the mechanisms regulating flagellar biogenesis in Y. pseudotuberculosis may differ from those described for other bacteria.

The Helicobacter pylori anti-sigma factor FlgM is predominantly cytoplasmic and cooperates with the flagellar basal body protein FlhA

Helicobacter pylori requires flagellar motility and orientation to persist actively in its habitat. A particular feature of flagella in most Helicobacter species including H. pylori is a membraneous flagellar sheath. The anti-sigma factor FlgM of H. pylori is unusual, since it lacks an N-terminal domain present in other FlgM homologs, e.g., FlgM of Salmonella spp., whose regulatory function is intimately coupled to its secretion through the flagellar type III secretion system. The aim of the present study was to characterize the localization and secretion of the short H. pylori FlgM in the presence of a flagellar sheath and to elucidate its interaction with other flagellar proteins, such as the basal body protein FlhA, which was previously shown to cooperate with FlgM for regulation. H. pylori FlgM was only released into the medium in minor amounts in wild-type bacteria, where the bulk amount of the protein was retained in the cytoplasm. Some FlgM was detected in the flagellar fraction. FlgM was expressed in flhA mutants and was less soluble and differentially localized in bacterial fractions of the flhA mutant in comparison to wild-type bacteria. FlgM-green fluorescent protein and FlgM-V5 translational fusions were generated and expressed in H. pylori. FlgM displayed a predominantly polar distribution and interacted with the C-terminal domain of FlhA (FlhA(C)). We suggest that, in H. pylori, FlgM secretion may not be paramount for its regulatory function and that protein interactions at the flagellar basal body may determine the turnover and localization of functional FlgM.