Purification and characterization of a Shigella dysenteriae 1-like toxin produced by Escherichia coli

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Abstract
A toxin from an enteropathogenic strain of (E. coli H30) was purified to apparent homogeneity from cell lysates. The steps used to isolate the E. coli H30 toxin included French pressure-cell disruption of bacteria grown in Fe-depleted media, Affi-Gel Blue chromatography, chromatofocusing and anti-Shiga toxin affinity chromatography. The mobilities of the subunits of radioiodinated E. coli H30 toxin and Shiga toxin observed after the 2 toxins were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis were identical. In the absence of 2-mercaptoethanol, a narrow band was seen at MW 31,500 (.+-. 1000); a wide heavy band was observed between MW 4000 and 15,000. In the presence of 2-mercaptoethanol, bands were seen at MW 31,500 (.+-. 1,000), 27,000 and 4000-15,000. Other similarities between purified E. coli H30 and Shiga 60R toxins included identical isoelectric points (7.03 .+-. 0.02); comparable biological activities, i.e., cytotoxicity, lethality for mice and enterotoxicity; and the same relative heat stabilities (up to 65.degree. C for 30 min). The toxins apparently had different MW as determined by sucrose gradient analysis, gel filtration and cross-linking experiments with dimethyl suberimidate. The MW of native E. coli H30 toxin estimated from cross-linking studies was 48,000; the estimated MW of Shiga 60R toxin was 58,000. Apparently, like the cholera.sbd.E. coli.sbd.heat-labile toxin family, a family of Shiga-like toxins exists.