The exoenzyme S regulon is a set of coordinately regulated virulence genes of Pseudomonas aeruginosa. Proteins encoded by the regulon include a type III secretion and translocation apparatus, regulators of gene expression, and effector proteins. The effector proteins include two enzymes with ADP-ribosyltransferase activity (ExoS and ExoT) and an acute cytotoxin (ExoU). In this study, we identified ExoY as a fourth effector protein of the regulon. ExoY is homologous to the extracellular adenylate cyclases of Bordetella pertussis (CyaA) and Bacillus anthracis (EF). The homology among the three adenylate cyclases is limited to two short regions, one of which possesses an ATP-binding motif. In assays for adenylate cyclase activity, recombinant ExoY (rExoY) catalyzed the formation of cAMP with a specific activity similar to the basal activity of CyaA. In contrast to CyaA and EF, rExoY activity was not stimulated or activated by calmodulin. A 500-fold stimulation of activity was detected following the addition of a cytosolic extract from Chinese hamster ovary (CHO) cells. These results indicate that a eukaryotic factor, distinct from calmodulin, enhances rExoY catalysis. Site-directed mutagenesis of residues within the putative active site of ExoY abolished adenylate cyclase activity. Infection of CHO cells with ExoY-producing strains of P. aeruginosa resulted in the intracellular accumulation of cAMP. cAMP accumulation within CHO cells depended on an intact type III translocation apparatus, demonstrating that ExoY is directly translocated into the eukaryotic cytosol.

Pseudomonas aeruginosa is a gram-negative pathogen causing life-threatening infections. Lung injury and the development of sepsis depend largely on the expression of type III secretion system (TTSS) virulence. TTSS functions as a molecular syringe to deliver toxins directly to the cytosol of cells, inhibit innate immune mechanisms, and prevent bacterial clearance. Polyclonal antibodies that bind to PcrV of P. aeruginosa inhibit the delivery of type III toxins and enhance the clearance of bacteria during acute lung infections. PcrV is a homologue of LcrV, a protective antigen in the Yersinia TTSS and an integral component of TTSS. In this study, a murine monoclonal antibody (MAb) to PcrV was generated: MAb 166, which is protective against P. aeruginosa when coinstilled with the bacterial inoculum or intraperitoneally transferred to mice. Fab fragments from MAb 166 prevent sepsis and death. The epitope bound by MAb 166 was mapped to the carboxyl-terminus of PcrV.

Summary Pseudomonas aeruginosa delivers exoenzyme S (ExoS

The presence of invasion-inhibitory activity that is regulated by the transcriptional activator ExsA of cytotoxic Pseudomonas aeruginosa has previously been proposed. The results of this study show that both ExoT and ExoS, known type III secreted effector proteins of P. aeruginosa that are regulated by ExsA, possess this activity. Invasion was reduced 94.4% by ExoT and 96.0% by ExoS. Invasion-inhibitory activity is not linked to ADP-ribosylation activity, at least for ExoS, since a noncatalytic mutant also inhibits uptake by an epithelial cell line (invasion was reduced 96.0% by ExoSE381A).

AMPD1 genotype, relative fiber type composition, training status, and gender were evaluated as contributing factors to the reported variation in AMP deaminase enzyme activity in healthy skeletal muscle. Multifactorial correlative analyses demonstrate that AMPD1 genotype has the greatest effect on enzyme activity. An AMPD1 mutant allele frequency of 13.7 and a 1.7% incidence of enzyme deficiency was found across 175 healthy subjects. Homozygotes for the AMPD1 normal allele have high enzyme activities, and heterozygotes display intermediate activities. When examined according to genotype, other factors were found to affect variability as follows: AMP deaminase activity in homozygotes for the normal allele exhibits a negative correlation with the relative percentage of type I fibers and training status. Conversely, residual AMP deaminase activity in homozygotes for the mutant allele displays a positive correlation with the relative percentage of type I fibers. Opposing correlations in different homozygous AMPD1 genotypes are likely due to relative fiber-type differences in the expression of AMPD1 and AMPD3 isoforms. Gender also contributes to variation in total skeletal muscle AMP deaminase activity, with normal homozygous and heterozygous women showing only 85-88% of the levels observed in genotype-matched men.