B-146. Receptor Recognition by Shiga Toxin 2 Variants

C. Fuller-Schaefer, S. S. Iyer, A. A. Weiss;
Univ. of Cincinnati, Cincinnati, OH.

Shiga toxin includes two major antigenic forms (Stx1 and Stx2) as well as minor variants of Stx2 (Stx2a-Stx2g). Studies in primates have shown that administration of Stx2 (also known as Stx2a) alone can produce the symptoms of hemolytic uremic syndrome (HUS), while administration of Stx1 at the same dose does not lead to development of HUS. The potency of other Stx2 variants has been less well studied. Epidemiologic studies suggest that individuals infected with strains expressing Stx2a and Stx2c are more likely to develop HUS than individuals infected with strains expressing Stx2b and Stx2d. However, non-Stx2a serotypes are only rarely expressed by O157:H7 strains and it is likely that properties associated with E. coli strain also contribute to the development of HUS. Stx is an AB5 toxin. The enzymatically active A-subunit inhibits protein synthesis. The B-pentamer binds to host glycolipid receptors and delivers the A-subunit to the cytoplasm. Receptor recognition appears to influence both potency and host range. Stx1 and Stx2a both recognize globotriaosylceramide (Gb3), but Stx1 has a higher affinity for Gb3 than Stx2 and potency appears to be associated with less avid binding. Interestingly, Stx2e recognizes both Gb3 and Gb4, and strains expressing Stx2e are commonly associated with edema disease in piglets, but not HUS in humans. We have examined receptor recognition as a first step to defining the potency of the Stx2 variants. We have developed synthetic forms of Gb3 and variants of Gb3 that are N-acetylated on one or both of the two terminal sugars. Previously we have shown that Stx1 binds avidly to the synthetic Gb3, but less well to the N-acetylated analogues. In contrast, Stx2a binds well to the N-acetylated variants, but recognizes Gb3 very poorly. In the current studies we have used ELISA assays and surface plasmon resonance (Biacore) to assess the binding properties of the Stx2 variants. The binding properties of Stx2d are similar to those of Stx2a. Interestingly Stx2c binds more avidly to the N-acetylated analogues than Stx2a. Studies are underway to determine if avid binding to the N-acetylated analogues is associated with potency.