FIG 6.
Purified YopK protein inhibits bacterial adhesion to HeLa cells. HeLa cells seeded in 12-well plates were grown to 80% confluence in the presence of 1 μM cytochalasin D. About 50 μg/ml of purified GST-YopK or GST-YopKΔ91–124 was added to the cell cultures, and then the cells were infected with the wild-type or ΔyopK Y. pestis strain at an MOI of 100. After 2 h of infection, cells were extensively washed in prewarmed PBS to remove the unattached bacteria and then lysed in 0.1% Triton X-100. The percentage of adhesion was determined as described for Fig. 3A. Addition of purified GST-YopK significantly lowered the adhesion of ΔyopK bacteria to HeLa cells, but addition of purified GST-YopKΔ91–124 exhibited no such effect. Two-way ANOVA with Bonferroni's multiple-comparison test was performed to analyze the significance of difference in bacterial adhesion between the different treatments (ns, not significant; *, P < 0.05; **, P < 0.01; ***, P < 0.001).