Enterohaemorrhagic Escherichia coli haemolysin is cleaved and inactivated by serine protease EspPα.
Bottom Line: In a cellular infection system, the cytolytic potential of EHEC-Hly-secreting recombinant strains was abolished when EspPα was coexpressed.We propose the concept of bacterial effector molecule interference (BEMI), reflecting the concerted interplay of virulence factors.Interference between effector molecules might be an additional way to regulate virulence functions and increases the complexity of monomolecular phenotypes.
Affiliation: Institute of Food Chemistry, University of Münster, Corrensstrasse 45, Münster, Germany. email@example.comShow MeSH
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Mentions: To investigate if the cleavage of EHEC-Hly by EspP might have biological implications during an EHEC infection, we used a model of human brain microvascular endothelial cells (HBMECs). The brain microvasculature is a target during EHEC-mediated HUS and these cells are highly susceptible to the cytolytic effect of EHEC-Hly (Aldick et al., 2007). Cultured HBMECs were first exposed to supernatants of overnight cultures of clones TA145/TA144 and TA143/TA142 producing EHEC-Hly from EHEC O157 and EHEC O26, respectively, together with proteolytically active/inactive EspPα, and HBMEC lysis was monitored by measuring release of intracellular lactate dehydrogenase (LDH). In both pairs, the clones expressing EHEC-Hly together with inactive EspPα (TA144 and TA142) caused lysis of HBMECs which was low, but significantly higher than that caused by the clones that express EHEC-Hly together with the proteolytically active EspPα (TA145 and TA143) (Fig. 5A). To enhance the effect of EHEC-Hly on the target cells, we next infected the HBMEC monolayers with living bacteria which continuously produce the toxin, increasing therefore the probability of its interaction with the cells. After 4 h exposure of HBMECs to the bacterial cultures and subsequent post-incubation for 18 h, clones TA144 and TA142 caused a pronounced dose-dependent lysis of HBMECs, whereas clones TA145 and TA143 caused only baseline and dose-independent LDH release (Fig. 5B and C). This suggests that cleavage of EHEC-Hly by EspPα might prevent the lytic effect of the toxin on the target cells.
Affiliation: Institute of Food Chemistry, University of Münster, Corrensstrasse 45, Münster, Germany. firstname.lastname@example.org