کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
2187750 1096138 2008 11 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Conformational Changes and Reaction of Clostridial Glycosylating Toxins
موضوعات مرتبط
علوم زیستی و بیوفناوری بیوشیمی، ژنتیک و زیست شناسی مولکولی بیولوژی سلول
پیش نمایش صفحه اول مقاله
Conformational Changes and Reaction of Clostridial Glycosylating Toxins
چکیده انگلیسی

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.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Molecular Biology - Volume 377, Issue 5, 11 April 2008, Pages 1346–1356
نویسندگان
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