Characterization of pic, a secreted protease of Shigella flexneri and enteroaggregative Escherichia coli

We have identified and characterized a secreted protein, designated Pie, wh ich is encoded on the chromosomes of enteroaggregative Escherichia coli (EA EC) 042 and Shigella flexneri 2457T. The product of the pic gene is synthes ized as a 146.5-kDa precursor molecule which is processed at the N and C te rmini during secretion, allowing the release of a mature protein (109.8 kDa ) into the culture supernatant. The deduced amino acid sequence of Pic show s high homology to autotransporter proteins, particularly a subgroup termed the SPATEs (serine protease autotransporters of the Enterobacteriaceae). P resent in all members of this subgroup is a motif similar to the active sit es of certain serine proteases. Pic catalyzes gelatin degradation, which ca n be abolished by disruption of the predicted proteolytic active site. Func tional analysis of the Pic protein implicates this factor in mucinase activ ity, serum resistance, and hemagglutination. Our data suggest that Pic may be a multifunctional protein involved in enteric pathogenesis.