Difference in protein substrate specificity between hemorrhagic toxin and lethal toxin from Clostridium sordellii

The hemorrhagic toxin (HT) from Clostridium sordellii is pharmacologically related to Clostridium difficile toxins A and B and Clostridium sordellii lethal toxin which have been recently identified as mono-glucosyl-transferases. Here we report that HT, which is coexpressed with lethal toxin, is also a glucosyltransferase. Whereas lethal toxin glucosylates the Rho subfamily proteins Rac and Cdc42 and the Ras subfamily proteins H-Ras and Rap, the substrate specificity of HT is strictly confined to the Rho subfamily proteins Rho, Rac and Cdc42. Comparable to lethal toxin, transferase activity of HT is stimulated by Mn2+. Acceptor amino acid in Rho was identified by mutagenesis as threonine-37. C. sordellii HT is a novel member of the family of clostridial mono-glucosyl-transferases, a family which modifies the Rho and Ras GTPases.