Calcium-independent calmodulin binding and two-metal-ion catalytic mechanism of anthrax edema factor
Calcium-independent calmodulin binding and two-metal-ion catalytic mechanism of anthrax edema factor
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DOI：
10.1038/sj.emboj.7600574
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发表时间：
2005-03-09
期刊：
影响因子：
11.4
通讯作者：
Tang, WJ
中科院分区：
文献类型：
--
作者：
Shen, YQ;Zhukovskaya, NL;Tang, WJ
水肿因子（EF）是炭疽外毒素中的一个关键因子，具有炭疽保护性抗原结合结构域（PABD）和钙调素（CaM）激活的腺苷酸环化酶结构域。在这里，我们报告钙调素结合EF的晶体结构，揭示EF PABD的架构。CaM具有N端和C端结构域，每个结构域可以结合两个钙离子。钙离子结合导致钙调素的构象由封闭型向开放型转变。EF-CaM复合物的结构显示EF如何将CaM的N-末端结构域锁定成闭合构象，而不管其钙负载状态如何。这代表了CaM效应子如何改变CaM的钙亲和力并使CaM的构象变化与钙负荷解偶联的机制。此外，与核苷酸复合的EF - CaM的结构表明EF使用双金属离子催化，这是DNA和RNA聚合酶中普遍存在的机制。组氨酸（H351）通过活化水以使ATP的3 'OH去质子化而进一步促进EF的催化。哺乳动物腺苷酸环化酶与EF没有结构相似性，并且它们也使用双金属离子催化，这表明两种结构不同的腺苷酸环化酶的催化机制驱动的趋同进化。
Edema factor (EF), a key anthrax exotoxin, has an anthrax protective antigen-binding domain (PABD) and a calmodulin (CaM)-activated adenylyl cyclase domain. Here, we report the crystal structures of CaM-bound EF, revealing the architecture of EF PABD. CaM has N- and C-terminal domains and each domain can bind two calcium ions. Calcium binding induces the conformational change of CaM from closed to open. Structures of the EF - CaM complex show how EF locks the N- terminal domain of CaM into a closed conformation regardless of its calcium-loading state. This represents a mechanism of how CaM effector alters the calcium affinity of CaM and uncouples the conformational change of CaM from calcium loading. Furthermore, structures of EF - CaM complexed with nucleotides show that EF uses two- metal - ion catalysis, a prevalent mechanism in DNA and RNA polymerases. A histidine (H351) further facilitates the catalysis of EF by activating a water to deprotonate 3'OH of ATP. Mammalian adenylyl cyclases share no structural similarity with EF and they also use two- metal - ion catalysis, suggesting the catalytic mechanism-driven convergent evolution of two structurally diverse adenylyl cyclases.