The Yersinia pseudotuberculosis YplA phospholipase differs in its activity, regulation and secretion from that of the Yersinia enterocolitica YplA.

Analysis of the Yersinia pseudotuberculosis and Yersinia pestis genomes indicates that both species carry an identical copy of a gene that is predicted to encode a protein which shares 80% similarity to the Yersinia enterocolitica YplA, a secreted phospholipase that has been shown to contribute to virulence. In contrast to well tolerated production of the Y. enterocolitica YplA in Escherichia coli, Y. pseudotuberculosis YplA expression was found to be toxic; however, cell viability could be restored if the Y. pseudotuberculosis YplA was expressed in the presence of its accessory protein YplB. In vitro, Y. pseudotuberculosis YplB was shown to reduce the activity of its cognate phospholipase in a dose-dependent manner. To determine whether the Y. pseudotuberculosis and Y. enterocolitica YplAs were secreted and regulated in a similar manner, secretion and promoter activity assays were performed. Unlike the situation apparent in Y. enterocolitica, expression of the Y. pseudotuberculosis yplA gene did not appear to be controlled by the flagellar regulon, nor did the phospholipase appear to be efficiently exported through the flagellar apparatus. These results indicate that the Yersinia YplAs vary in many of their attributes despite their high degree of amino acid homology.

Cytotoxic necrotizing factor type 1-neutralizing monoclonal antibody NG8 recognizes three amino acids in a C-terminal region of the toxin and reduces toxin binding to HEp-2 cells.

Cytotoxic necrotizing factor type 1 (CNF1) and CNF2 are toxins of pathogenic Escherichia coli that share 85% identity over 1,014 amino acids. Although both of these toxins modify GTPases, CNF1 is a more potent inducer of multinucleation in HEp-2 cells, binds more efficiently to HEp-2 cells, and, despite the conservation of amino acids (C866 and H881) required for enzymatic activity of the toxins, deamidates RhoA and Cdc42 better than CNF2. Here we exploited the differences between CNF1 and CNF2 to define the epitope on CNF1 to which the CNF1-specific neutralizing monoclonal antibody (MAb) (MAb NG8) binds and to determine the mechanism by which MAb NG8 neutralizes CNF1 activity on HEp-2 cells. For these purposes, we generated a panel of 21 site-directed mutants in which amino acids in CNF1 were exchanged for the amino acids in CNF2 between amino acids 546 and 869 and vice versa. This region of CNF1 not only is recognized by MAb NG8 but also is involved in binding of this toxin to HEp-2 cells. All the mutants retained the capacity to induce multinucleation of HEp-2 cells. However, the CNF1 double mutant with D591E and F593L mutations (CNF1(D591E F593L)) and the CNF1(H661Q) single mutant displayed drastically reduced reactivity with MAb NG8. A reverse chimeric triple mutant, CNF1(E591D L593F Q661H), imparted MAb NG8 reactivity to CNF2. MAb NG8 neutralized CNF2(E591D L593F Q661H) activity in a dose-dependent manner and reduced the binding of this chimeric toxin to HEp-2 cells. Taken together, these results pinpoint three amino acids in CNF1 that are key amino acids for recognition by neutralizing MAb NG8 and further help define a region in CNF1 that is critical for full toxin binding to HEp-2 cells.

Two domains of cytotoxic necrotizing factor type 1 bind the cellular receptor, laminin receptor precursor protein.

Cytotoxic necrotizing factor type 1 (CNF1) and CNF2 are highly homologous toxins that are produced by certain pathogenic strains of Escherichia coli. These 1,014-amino-acid toxins catalyze the deamidation of a specific glutamine residue in RhoA, Rac1, and Cdc42 and consist of a putative N-terminal binding domain, a transmembrane region, and a C-terminal catalytic domain. To define the regions of CNF1 that are responsible for binding of the toxin to its cellular receptor, the laminin receptor precursor protein (LRP), a series of CNF1 truncated toxins were characterized and assessed for toxin binding. In particular, three truncated toxins, DeltaN63, DeltaN545, and DeltaC469, retained conformational integrity and in vitro enzymatic activity and were immunologically reactive against a panel of anti-CNF1 monoclonal antibodies (MAbs). Based on a comparison of these truncated toxins with wild-type CNF1 and CNF2 in LRP and HEp-2 cell binding assays and in MAb and LRP competitive binding inhibition assays and based on the results of confocal microscopy, we concluded that CNF1 contains two major binding regions: one located within the N terminus, which contained amino acids 135 to 164, and one which resided in the C terminus and included amino acids 683 to 730. The data further indicate that CNF1 can bind to an additional receptor(s) on HEp-2 cells and that LRP can also serve as a cellular receptor for CNF2.

A single amino acid substitution in the enzymatic domain of cytotoxic necrotizing factor type 1 of Escherichia coli alters the tissue culture phenotype to that of the dermonecrotic toxin of Bordetella spp.

Cytotoxic necrotizing factor type 1 (CNF1) and dermonecrotic toxin (DNT) share homology within their catalytic domains and possess deamidase and transglutaminase activities. Although each toxin has a preferred enzymatic activity (i.e. deamidation for CNF1 and transglutamination for DNT) as well as target substrates, both modify a specific glutamine residue in RhoA, Rac1 and Cdc42, which renders these GTPases constitutively active. Here we show that despite their similar mechanisms of action CNF1 and DNT induced unique phenotypes on HEp-2 and Swiss 3T3 cells. CNF1 induced multinucleation of HEp-2 cells and was cytotoxic for Swiss 3T3 cells (with binucleation of the few surviving cells) while DNT showed no morphological effects on HEp-2 cells but did induce binucleation of Swiss 3T3 cells. To determine if the enzymatic domain of each toxin dictated the induced phenotype, we constructed enzymatically active chimeric toxins and mutant toxins that contained single amino acid substitutions within the catalytic site and tested these molecules in tissue culture and enzymatic assays. Moreover, both site-directed mutant toxins showed reduced time to maximum transglutamination of RhoA compared with the parent toxins. Nevertheless, the substitution of threonine for Lys(1310) in the DNT-based mutant, while affecting transglutamination efficiency of the toxin, did not abrogate that enzymatic activity.

Ferrets as a model system for renal disease secondary to intestinal infection with Escherichia coli O157:H7 and other Shiga toxin-producing E. coli.

Ferrets were evaluated as a possible small animal model for the development of colitis and/or signs of the hemolytic uremic syndrome after oral infection with Escherichia coli O157:H7 or other Shiga toxin--producing E. coli (STEC). Ferrets treated with streptomycin (Stm) had higher counts of E. coli O157:H7 strain 86-24 Stm-resistant (Stm(r)) or O91:H21 strain B2F1 Stm(r) in their stools than non--Stm-treated animals. None of the animals displayed evidence of colitis, but Stm-treated animals fed strain 86-24 Stm(r) exhibited weight loss significantly greater than that exhibited by ferrets fed an isogenic mutant negative for the adhesin intimin. Moreover, 11 (23%) of the 47 Stm-treated ferrets inoculated with 86-24 Stm(r) or B2F1 Stm(r) developed hematuria and/or histological damage to glomeruli or thrombocytopenia, compared with 0 of 14 uninfected control animals receiving Stm in water. Thus, the ferret may serve as a model for renal disease secondary to intestinal infection with STEC.