Reinert Dirk J, Jank Thomas, Aktories Klaus, Schulz Georg E
Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität, Albertstr. 21, 79104 Freiburg im Breisgau, Germany.
J Mol Biol. 2005 Sep 2;351(5):973-81. doi: 10.1016/j.jmb.2005.06.071.
Toxin B is a member of the family of large clostridial cytotoxins which are of great medical importance. Its catalytic fragment was crystallized in the presence of UDP-glucose and Mn2+. The structure was determined at 2.2 A resolution, showing that toxin B belongs to the glycosyltransferase type A family. However, toxin B contains as many as 309 residues in addition to the common chainfold, which most likely contribute to the target specificity. A superposition with other glycosyltransferases shows the expected positions of the acceptor oxygen atom during glucosyl transfer and indicates further that the reaction proceeds probably along a single-displacement pathway. The C1'' donor carbon atom position is defined by the bound UDP and glucose. It assigns the surface area of toxin B that forms the interface to the target protein during the modifying reaction. A docking attempt brought the known acceptor atom, Thr37 O(gamma1) of the switch I region of the RhoA:GDP target structure, near the expected position. The relative orientation of the two proteins was consistent with both being attached to a membrane. Sequence comparisons between toxin B variants revealed that the highest exchange rate occurs around the active center at the putative docking interface, presumably due to a continuous hit-and-evasion struggle between Clostridia and their eukaryotic hosts.
毒素B是具有重要医学意义的大型梭菌细胞毒素家族的成员。其催化片段在UDP-葡萄糖和Mn2+存在的情况下结晶。该结构在2.2埃分辨率下确定，表明毒素B属于A型糖基转移酶家族。然而，除了常见的链折叠外，毒素B还含有多达309个残基，这很可能有助于其靶标特异性。与其他糖基转移酶的叠加显示了葡萄糖基转移过程中受体氧原子的预期位置，并进一步表明该反应可能沿着单置换途径进行。C1''供体碳原子位置由结合的UDP和葡萄糖确定。它确定了毒素B在修饰反应过程中与靶蛋白形成界面的表面积。对接尝试使已知的受体原子，即RhoA:GDP靶标结构开关I区域的Thr37 O(γ1)，靠近预期位置。两种蛋白质的相对取向与它们都附着在膜上一致。毒素B变体之间的序列比较显示，最高交换率发生在假定对接界面的活性中心周围，这可能是由于梭菌与其真核宿主之间持续的攻击与逃避斗争。
