Conformational changes and reaction of clostridial glycosylating toxins |
| |
Authors: | Ziegler Mathias O P Jank Thomas Aktories Klaus Schulz Georg E |
| |
Affiliation: | 1 Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität, Albertstr. 21, D-79104 Freiburg im Breisgau, Germany 2 Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Albert-Ludwigs-Universität, Albertstr. 25, 79104 Freiburg im Breisgau, Germany |
| |
Abstract: | The crystal structures of the catalytic fragments of ‘lethal toxin’ from Clostridium sordellii and of ‘α-toxin’ from Clostridium novyi have been established. Almost half of the residues follow the chain fold of the glycosyl-transferase type A family of enzymes; the other half forms large α-helical protrusions that are likely to confer specificity for the respective targeted subgroup of Rho proteins in the cell. In the crystal, the active center of α-toxin contained no substrates and was disassembled, whereas that of lethal toxin, which was ligated with the donor substrate UDP-glucose and cofactor Mn2 +, was catalytically competent. Surprisingly, the structure of lethal toxin with Ca2 + (instead of Mn2 +) at the cofactor position showed a bound donor substrate with a disassembled active center, indicating that the strictly octahedral coordination sphere of Mn2 + is indispensable to the integrity of the enzyme. The homologous structures of α-toxin without substrate, distorted lethal toxin with Ca2 + plus donor, active lethal toxin with Mn2 + plus donor and the homologous Clostridium difficile toxin B with a hydrolyzed donor have been lined up to show the geometry of several reaction steps. Interestingly, the structural refinement of one of the three crystallographically independent molecules of Ca2 +-ligated lethal toxin resulted in the glucosyl half-chair conformation expected for glycosyl-transferases that retain the anomeric configuration at the C1″ atom. A superposition of six acceptor substrates bound to homologous enzymes yielded the position of the nucleophilic acceptor atom with a deviation of < 1 Å. The resulting donor-acceptor geometry suggests that the reaction runs as a circular electron transfer in a six-membered ring, which involves the deprotonation of the nucleophile by the β-phosphoryl group of the donor substrate UDP-glucose. |
| |
Keywords: | UDP-GlcNAc, UDP-N-acetylglucosamine UDP-Glc, UDP-glucose ToxB, catalytic fragment of toxin B from Clostridium difficile GT-A, glycosyl-transferase type A LT, catalytic fragment of lethal toxin from Clostridium sordellii αTox, catalytic fragment of α-toxin from Clostridium novyi Ca-LT, LT crystal containing Ca2 + and UDP-Glc Mn-LT, LT crystal containing Mn2 + and UDP-Glc Glc, smallcaps" >d-glucose |
本文献已被 ScienceDirect PubMed 等数据库收录! |
|