J. Bacteriol., Feb 1997, 987-997, Vol 179, No. 4
A Schmitz, C Josenhans and S Suerbaum
Flagellar motility has been shown to be an essential requirement for the
ability of Helicobacter pylori to colonize the gastric mucosa. While some
flagellar structural components have been studied in molecular detail,
nothing was known about factors that play a role in the regulation of
flagellar biogenesis. We have cloned and characterized an H. pylori homolog
(named flbA) of the lcrD/flbF family of genes. Many proteins encoded by
these genes are known to be involved in flagellar biogenesis or secretion
of virulence-associated proteins via type III secretion systems. The H.
pylori flbA gene (2,196 bp) is capable of coding for a predicted
732-amino-acid, 80.9-kDa protein that has marked sequence similarity with
other known members of the LcrD/FlbF protein family. An isogenic strain
with a mutation in the flbA gene was constructed by disruption of the gene
with a kanamycin resistance cassette and electroporation-mediated allelic
exchange mutagenesis. The mutant strain expressed neither the FlaA nor the
FlaB flagellin protein. The expression of the FlgE hook protein was reduced
in comparison with the wild-type strain, and the extent of this reduction
was growth phase dependent. The flbA gene disruption was shown to
downregulate the expression of these flagellar genes on the transcriptional
level. The flbA mutants were aflagellate and completely nonmotile.
Occasionally, assembled hook structures could be observed, indicating that
export of axial flagellar filament components was still possible in the
absence of the flbA gene product. The hydrophilic part of the FlbA protein
was expressed in Escherichia coli, purified, and used to raise a polyclonal
rabbit antiserum against the FlbA protein. Western blot experiments with
this antiserum indicated that the FlbA protein is predominantly associated
with the cytoplasmic membrane in H. pylori. The antiserum cross-reacted
with two other proteins (97 and 43 kDa) whose expression was not affected
by the flbA gene disruption and which might represent further H. pylori
homologs of the LcrD/FlbF protein family.
Copyright © 1997, American Society for Microbiology
Cloning and characterization of the Helicobacter pylori flbA gene, which codes for a membrane protein involved in coordinated expression of flagellar genes
Ruhr-Universitat Bochum, Medizinische Mikrobiologie und Immunologie, Germany.
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