Cloning and sequencing of the Bordetella pertussis cpn10/cpn60 (groESL) homolog

Adjuvant and immunogenic activities of the 73kDa N-terminal alpha-domain of BrkA autotransporter and Cpn60/60kDa chaperonin of Bordetella pertussis

A soluble fraction obtained from Bordetella pertussis was evaluated as adjuvant for the pertussis component of the Diphtheria-Pertussis-Tetanus (DPT) vaccine. High levels of antibodies were induced, and a 78% protection rate of mice challenged with live B. pertussis was observed. Two proteins were identified as the 73 kDa N-terminal alpha-domain of BrkA autotransporter protein and the Cpn60/60 kDa chaperonin. Both stimulated antibodies against pertussis and induced a 42% protection rate against the challenge. IgG1 and IgG2a were stimulated suggesting that the immune response could be modulated to produce Th1 or Th2.

CtsR is the master regulator of stress response gene expression in Oenococcus oeni

Although many stress response genes have been characterized in Oenococcus oeni, little is known about the regulation of stress response in this malolactic bacterium. The expression of eubacterial stress genes is controlled both positively and negatively at the transcriptional level. Overall, negative regulation of heat shock genes appears to be more widespread among gram-positive bacteria. We recently identified an ortholog of the ctsR gene in O. oeni. In Bacillus subtilis, CtsR negatively regulates expression of the clp genes, which belong to the class III family of heat shock genes. The ctsR gene of O. oeni is cotranscribed with the downstream clpC gene. Sequence analysis of the O. oeni IOB 8413 (ATCC BAA-1163) genome revealed the presence of potential CtsR operator sites upstream from most of the major molecular chaperone genes, including the clp genes and the groES and dnaK operons. Using B. subtilis as a heterologous host, CtsR-dependent regulation of O. oeni molecular chaperone genes was demonstrated with transcriptional fusions. No alternative sigma factors appear to be encoded by the O. oeni IOB 8413 (ATCC BAA-1163) genome. Moreover, apart from CtsR, no known genes encoding regulators of stress response, such as HrcA, could be identified in this genome. Unlike the multiple regulatory mechanisms of stress response described in many closely related gram-positive bacteria, this is the first example where dnaK and groESL are controlled by CtsR but not by HrcA.

The PtlE protein of Bordetella pertussis has peptidoglycanase activity required for Ptl-mediated pertussis toxin secretion

Pertussis toxin of Bordetella pertussis is secreted by a type IV secretion system comprised of the products of the nine ptl (pertussis toxin liberation) genes. These proteins are believed to form a complex spanning both the inner and outer membranes and passing through the peptidoglycan layer. Peptidoglycan acts as a barrier for transport through the periplasm of large folded molecules. Assembled pertussis toxin and the secretion component proteins PtlC through PtlH are too large to diffuse through intact peptidoglycan. Therefore, we hypothesized that the Ptl system contains a peptidoglycanase activity. The PtlE protein was found to exhibit a sequence match to the active site of glycohydrolase enzymes. An N-terminally polyhistidine-tagged PtlE fusion protein, constructed and expressed in Escherichia coli and in B. pertussis, exhibited peptidoglycanase activity on activity gels. A fusion protein with alanine substitutions at the putative active site residues (aspartic acid at position 53 and glutamic acid at position 62) lacked peptidoglycanase activity. B. pertussis strains with the amino acid substitutions were deficient for pertussis toxin secretion. Based on these results, we concluded that PtlE is a peptidoglycanase responsible for the local removal or rearrangement of the peptidoglycan layer during Ptl secretion complex assembly.

Fluorescent labels influence phagocytosis of Bordetella pertussis by human neutrophils

To explore the role of neutrophil phagocytosis in host defense against Bordetella pertussis, bacteria were labeled extrinsically with fluorescein isothiocyanate (FITC) or genetically with green fluorescent protein (GFP) and incubated with adherent human neutrophils in the presence or absence of heat-inactivated human immune serum. In the absence of antibodies, FITC-labeled bacteria were located primarily on the surface of the neutrophils with few bacteria ingested. However, after opsonization, about seven times more bacteria were located intracellularly, indicating that antibodies promoted phagocytosis. In contrast, bacteria labeled intrinsically with GFP were not efficiently phagocytosed even in the presence of opsonizing antibodies, suggesting that FITC interfered with a bacterial defense. Because FITC covalently modifies proteins and could affect their function, we tested the effect of FITC on adenylate cyclase toxin activity, an important extracellular virulence factor. FITC-labeled bacteria had fivefold-less adenylate cyclase toxin activity than did unlabeled wild-type bacteria or GFP-expressing bacteria, suggesting that FITC compromised adenylate cyclase toxin activity. These data demonstrated that at least one extracellular virulence factor was affected by FITC labeling and that GFP is a more appropriate label for B. pertussis.

Transcriptional analysis of the groESL operon of Neisseria gonorrhoeae

The nucleotide sequence upstream of the groEL gene of Neisseria gonorrhoeae has been determined. Upstream of groEL is a homolog of groES and the divergently transcribed frpB gene. The promoter region of groES lacks the inverted repeat sequences (IR) that act as a regulatory element controlling the expression of similar operons in many other bacterial species. This region contains overlapping consensus sequences for sigma 32-dependent and sigma 70-dependent promoters, and an appropriately placed transcription start point was mapped downstream of these promoters. Northern hybridization demonstrated that synthesis of a full-length groES-groEL transcript was induced in heat-stressed cells. These experiments also revealed the presence of a shorter groES-specific transcript, apparently the result of the premature termination of transcription at an IR situated between the groES and groEL genes.

Identification of a Caulobacter crescentus operon encoding hrcA, involved in negatively regulating heat-inducible transcription, and the chaperone gene grpE

In response to elevated temperature, both prokaryotic and eukaryotic cells increase expression of a small family of chaperones. The regulatory network that functions to control the transcription of the heat shock genes in bacteria includes unique structural motifs in the promoter region of these genes and the expression of alternate sigma factors. One of the conserved structural motifs, the inverted repeat CIRCE element, is found in the 5' region of many heat shock operons, including the Caulobacter crescentus groESL operon. We report the identification of another C. crescentus heat shock operon containing two genes, hrcA (hrc for heat shock regulation at CIRCE elements) and a grpE homolog. Disruption of the hrcA gene, homologs of which are also found upstream of grpE in other bacteria, increased transcription of the groESL operon, and this effect was dependent on the presence of an intact CIRCE element. This suggests a role for HrcA in negative regulation of heat shock gene expression. We identified a major promoter transcribing both hrcA and grpE and a minor promoter located within the hrcA coding sequence just upstream of grpE. Both promoters were heat shock inducible, with maximal expression 10 to 20 min after heat shock. Both promoters were also expressed constitutively throughout the cell cycle under physiological conditions. C. crescentus GrpE, shown to be essential for viability at low and high temperatures, complemented an Escherichia coli delta grpE strain in spite of significant differences in the N- and C-terminal regions of these two proteins, demonstrating functional conservation of this important stress protein.