StcE of Escherichia Coli O157:H7

Enterohemorrhagic E. coli (EHEC) is a food-borne pathogen that causes watery diarrhea and hemorrhagic colitis. Approximately four percent of HC cases progress to hemolytic uremic syndrome (HUS), with a higher incidence in children under 10 years of age. Our laboratory previously described StcE, a zinc metalloprotease with complement-regulating and mucinase activity secreted from E. coli O157:H7. These effects are accomplished through interaction with C1 esterase inhibitor (C1-INH), a host negative regulator of complement, and mucins, heavily glycosylated proteins that form the protective mucus throughout the gastrointestinal tract. StcE binds glycoproteins containing mucin-like regions of densely-attached O-glycans. StcE affinity for C1-INH is not decreased by the addition of soluble sugars or SNA lectin, and StcE does not bind glycans similar in structure to the described C1-INH glycans, as assessed by glycan array analysis. Removal of glycosylations abrogates StcE activity against C1-INH. However, alteration of the glycan structures through expression of C1-INH in Lec glycosylation mutants did not affect proteolysis of the C1-INH glycoforms. These data suggest that StcE recognizes the extended random coil conformation characteristic of mucins. In a separate project, we identified StcE in culture supernatants of atypical Shigella boydii 13 (Shigella B13) strains. Further examination of the Shigella B13 strains reveal that this cluster of pathogens does not invade but forms pedestals on HEp-2 cells similar to EHEC and enteropathogenic E. coli (EPEC). We also demonstrated that atypical Shigella B13 evolution recapitulates the progression from ancestral EPEC to EHEC on a Shigella background phenotype.