SummaryChlamydia pneumoniae, an obligate intracellular human pathogen, causes a number of respiratory diseases. We explored the role of the conserved OmcB protein in C. pneumoniae infections, using yeast display technology. OmcB from Chlamydia trachomatis serovar L1 also adheres to human cells in a heparin-dependent way, unlike its counterpart from serovar E. We show that a single position in the OmcB sequence determines heparin dependence/independence, and variations there may reflect differences between the two serovars in cell tropism and disease pattern.

SummaryCell division and cell wall biosynthesis in prokaryotes are driven by partially overlapping multiprotein machineries whose activities are tightly controlled and co-ordinated. So far, a number of protein components have been identified and acknowledged as essential for both fundamental cellular processes. Genes for enzymes of both machineries have been found in the genomes of the cell wall-less genera Chlamydia and Wolbachia, raising questions as to the functionality of the lipid II biosynthesis pathway and reasons for its conservation. We provide evidence on three levels that the lipid II biosynthesis pathway is indeed functional and essential in both genera: (i) fosfomycin, an inhibitor of MurA, catalysing the initial reaction in lipid II biosynthesis, has a detrimental effect on growth of Wolbachia cells; (ii) isolated cytoplasmic membranes from Wolbachia synthesize lipid II ex vivo; and (iii) recombinant MraY and MurG from Chlamydia and Wolbachia exhibit in vitro activity, synthesizing lipid I and lipid II respectively. We discuss the hypothesis that the necessity for maintaining lipid II biosynthesis in cell wall-lacking bacteria reflects an essential role of the precursor in prokaryotic cell division. Our results also indicate that the lipid II pathway may be exploited as an antibacterial target for chlamydial and filarial infections.

In a previous study, we reported that the OmcB protein from Chlamydia pneumoniae mediates adhesion of the infectious elementary body to human HEp-2 cells by interacting with heparin/heparan sulfate-like glycosaminoglycans (GAGs) via basic amino acids located in the first of a pair of XBBXBX heparin-binding motifs (K. Moelleken and J. H. Hegemann, Mol. Microbiol. 67:403-419, 2008). In the present study, we show that the basic amino acid at position 57 (arginine) in the first XBBXBX motif, the basic amino acid at position 61 (arginine) in the second motif, and another amino acid (lysine 69) C terminal to it play key roles in the interaction. In addition, we show that discrimination between heparin-dependent and -independent adhesion by C. trachomatis OmcBs is entirely dependent on three variable amino acids in the so-called variable domain C terminal to the conserved XBBXBX motif. Here, the predicted conformational change in the secondary structure induced by the proline at position 66 seems to be crucial for heparin recognition. Finally, we performed neutralization experiments using different anti-heparan sulfate antibodies to gain insight into the nature of the GAGs recognized by OmcB. The results suggest that C. trachomatis serovar L2 OmcB interacts with 6-O-sulfated domains of heparan sulfate, while C. pneumoniae OmcB apparently interacts with domains of heparan sulfate harboring a diverse subset of O-sulfations.

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