Helena Louie

FlaC, a protein of Campylobacter jejuni TGH9011 (ATCC43431) secreted through the flagellar apparatus, binds epithelial cells and influences cell invasion.

Type III secretion systems identified in bacterial pathogens of animals and plants transpose effectors and toxins directly into the cytosol of host cells or into the extracellular milieu. Proteins of the type III secretion apparatus are conserved among diverse and distantly related bacteria. Many type III apparatus proteins have homologues in the flagellar export apparatus, supporting the notion that type III secretion systems evolved from the flagellar export apparatus. No type III secretion apparatus genes have been found in the complete genomic sequence of Campylobacter jejuni NCTC11168. In this study, we report the characterization of a protein designated FlaC of C. jejuni TGH9011. FlaC is homologous to the N‐ and C‐terminus of the C. jejuni flagellin proteins, FlaA and FlaB, but lacks the central portion of these proteins. flaC null mutants form a morphologically normal flagellum and are highly motile. In wild‐type C. jejuni cultures, FlaC is found predominantly in the extracellular milieu as a secreted protein. Null mutants of the flagellar basal rod gene (flgF) and hook gene (flgE) do not secrete FlaC, suggesting that a functional flagellar export apparatus is required for FlaC secretion. During C. jejuni infection in vitro, secreted FlaC and purified recombinant FlaC bind to HEp‐2 cells. Invasion of HEp‐2 cells by flaC null mutants was reduced to a level of 14% compared with wild type, suggesting that FlaC plays an important role in cell invasion.

Expression of the flgFG operon of Campylobacter jejuni in Escherichia coli yields an extra fusion protein.

Two Campylobacter jejuni genes with homology to the Escherichia coli flgF and flgG genes encoding two of the basal body rod proteins were isolated, and the nucleotide sequence was determined and analyzed. These two C. jejuni genes were shown, by Northern hybridization analysis, to function as a single operon (flgFG). Two transcriptional start sites were detected upstream of flgF, corresponding to the two RNA transcripts detected in the Northern blot. Western blot immunoassays using anti-FlgF and anti-FlgG antibodies demonstrated the synthesis of FlgF and FlgG proteins in C. jejuni and in Escherichia coli containing the C. jejuni flgF and flgG genes. Maxicell analysis and Western immunoblots using anti-FlgF antibodies to probe flgFG-encoded proteins in E. coli revealed the presence of a protein with a molecular mass of approximately the combined mass of the FlgF and FlgG proteins. Anti-FlgF antibodies detected in C. jejuni cell extracts the native FlgF protein and also a higher-molecular-weight protein that is likely encoded by the flgF and part of the flgG sequences.