Clostridium perfringens TpeL Glycosylates the Rac and Ras Subfamily Proteins

Clostridium perfringens TpeL belongs to a family of large clostridial cytotoxins that encompasses Clostridium difficile toxin A (TcdA) and B (TcdB) and Clostridium sordellii lethal toxin (TcsL). We report here the identification of the TpeL-catalyzed modification of small GTPases. A recombinant protein (TpeL1-525) derived from the TpeL N-terminal catalytic domain in the presence of streptolysin O (SLO) induced the rounding of Vero cells and the glycosylation of cellular Rac1. Among several hexoses tested, UDP-N-acetyl-glucosamine (UDP-GlcNAc) and UDP-glucose (UDP-Glc) served as cosubstrates for TpeL1-525-catalyzed modifications. TpeL1-525 catalyzed the incorporation of UDP-Glc into Ha-Ras, Rap1B, and RalA and of UDP-GlcNAc into Rac1, Ha-Ras, Rap1B, and RalA. In Rac1, TpeL and TcdB share the same acceptor amino acid for glycosylation, Thr-35. In Vero cells treated with TpeL1-525 in the presence of SLO, glycosylation leads to a translocation of the majority of Rac1 and Ha-Ras to the membrane. We demonstrate for first time that TpeL uses both UDP-GlcNAc and UDP-Glc as donor cosubstrates and modifies the Rac1 and Ras subfamily by glycosylation to mediate its cytotoxic effects.