Shiga toxin 2d B subunit (Stx2d-B)

Shiga toxin 2d (Stx2d) is a highly potent variant of the Shiga toxin 2 family produced by specific strains of Shiga toxin-producing Escherichia coli (STEC) (Melton-Celsa, 2014, Toxins). The B subunit of Stx2d forms a homopentameric structure that mediates the high-affinity binding of the holotoxin to the host cell surface glycolipid receptor, globotriaosylceramide (Gb3 or CD77) (Ling et al., 1998, Biochemistry). This binding event triggers receptor-mediated endocytosis, initiating the retrograde transport of the toxin through the Golgi apparatus to the endoplasmic reticulum (Sandvig & van Deurs, 2000, EMBO J). Stx2d is distinguished by its "activatable" property, where its biological activity is significantly enhanced upon cleavage of the A subunit by intestinal proteases like elastase, though the B subunit remains the critical delivery vehicle (Melton-Celsa et al., 1996, Infect. Immun.). The B subunit is a primary target for therapeutic intervention because blocking its interaction with Gb3 prevents the toxin from entering the cytosol and exerting its ribotoxic effects. Therapeutic development targeting the B subunit focuses on neutralizing antibodies and receptor mimics designed to block host cell attachment and prevent the development of life-threatening complications such as hemolytic uremic syndrome (HUS) (Lopez et al., 2010, Expert Opin. Biol. Ther.). Clinical challenges include the narrow window for treatment and the risk of increased toxin release if bacteria are lysed by certain antibiotics. Monitoring the presence of the stx2d gene and the B subunit protein is essential for identifying patients at high risk for severe disease progression.

Other names

Stx2d-BShiga-like toxin 2d B subunitVerotoxin 2d B subunitStx2d B-subunitShiga toxin 2 variant d B subunit

Neutralization of the toxin by binding to the B subunit pentamer, which prevents the toxin from interacting with the host cell receptor globotriaosylceramide (Gb3/CD77) and inhibits subsequent internalization.