The major virulence factors produced by Pseudomonas aeruginosa include secreted proteases that damage host tissues. Of the proteases analyzed, alkaline protease (AprA) and elastase B (LasB) have been characterized extensively. Although P. aeruginosa protein database predicts the presence of several other potential proteases, little has been known about the proteases involving in the pathogenicity of this organism. In this study, we found that P. aeruginosa produces a novel large extracellular protease (LepA) distinct from known proteases such as AprA and LasB. Sequence analysis of LepA showed a molecular future of the proteins transported by the two-partner secretion pathway. We demonstrated that LepA can activate NF-kB-driven promoter through protease-activated receptor-1, -2 or -4. On the other hand, one of the functions of proteases is to hydrolyze proteins and peptides for nutrient acquisition either by degrading host enzymes or even by causing tissue damage to further the survival of the bacterium. Therefore, to investigate the role of LepA in in vivo virulence and growth of P. aeruginosa, we compared the virulence and growth of a wild-type strain and its mutant using a mouse model of acute systemic infection by P. aeruginosa. Our results suggest that LepA contributes to the in vivo virulence and growth of P. aeruginosa.
Bacteria are known to regulate various gene expressions producing particular signal molecules termed “Auto-inducers” in the cell density-dependent manner. This physiological phenomenon termed “Quorum Sensing” has been discovered in many bacteria including normal bacterial flora and pathogens. Among Auto-inducers, Acyl-homoserine lactone has been best studied, which is leading with the human opportunistic pathogen, Pseudomonas aeruginosa. AHLs contain linear fatty-acyl side chains in the homoserine lactone moiety. Although the variation and specificity are determined by the sort of fatty acids, the number of fatty acid variations (approximately thirty) is absolutely less than that of AHL producers. However, new types of AHLs that have non-fatty acids in the side chain have been recently reported. This innovative finding enables to account for the diversity of AHL producing bacteria and also extend Quorum Sensing studies. In this paper, we will introduce novel classes of AHLs and their unique properties.