Samples were incubated in the presence (+) or absence (-) of trypsin HDAC inhibitor and analyzed by immunoblot analysis using polyclonal anti-VacA serum #958. To analyze potential differences in folding properties of the VacA mutant proteins compared to wild-type VacA, we analyzed the susceptibility of these proteins to proteolytic cleavage. Lysates of H. pylori strains were generated by sonication, and the solubilized proteins

were treated with trypsin as described in Methods. Trypsin digestion of two of the mutant proteins (Δ511-536 and Δ517-544) yielded proteolytic digest patterns that were identical to each other and similar to that of trypsin-digested wild-type VacA (Fig. 3B). Trypsin digestion of two other mutant proteins (Δ433-461 and Δ484-504) yielded different digest patterns, but these mutant proteins were not completely degraded (Fig. 3B). Four mutant proteins (Δ462-483, Δ559-579, Δ580-607, and Δ608-628) were completely degraded by trypsin (Fig. 3B). In general, the four mutant proteins that exhibited relative resistance to trypsin digestion were secreted at relatively high levels compared to mutant proteins that were completely degraded by trypsin (compare Fig. 2 and Fig. 3B). The observed variation among mutant VacA proteins in susceptibility to trypsin-mediated proteolysis suggested that the individual mutant proteins differed C188-9 in vitro in

folding properties. The proteins that were highly susceptible to trypsin digestion and secreted at very

low levels (Δ462-483, Δ559-579, Δ580-607, and Δ608-628) were probably misfolded. Due to the very low Urocanase concentrations of these four proteins in the broth culture supernatants, these mutant VacA proteins were not studied further. To evaluate whether the four mutant proteins exhibiting relative resistance to trypsin-mediated proteolysis (i.e. VacA Δ433-461, Δ484-504, Δ511-536, and Δ517-544) shared other features with wild-type VacA, we analyzed the reactivity of these proteins with an anti-VacA monoclonal antibody (5E4) that recognizes a conformational epitope [35]. Each of the four mutant VacA proteins was Q-VD-Oph chemical structure recognized by the 5E4 antibody (Fig. 4), which provided additional evidence that these mutant proteins were folded in a manner similar to that of wild-type VacA. Figure 4 Reactivity of VacA mutant proteins with a monoclonal anti-VacA antibody. Wild-type H. pylori strain 60190 and strains expressing mutant VacA proteins were grown in broth culture, and secreted VacA proteins were normalized as described in Methods. Wells of ELISA plates were coated with broth culture supernatants, and reactivity of the proteins with an anti-VacA monoclonal antibody (5E4) that recognizes a conformational epitope was determined by ELISA. Reactivity of a vacA null mutant was subtracted as background. Relative VacA concentrations are indicated. Values represent the mean ± SD from triplicate samples.