Structural insights into the reaction mechanism of S-adenosyl-L-homocysteine hydrolase.
Structural insights into the reaction mechanism of S-adenosyl-L-homocysteine hydrolase.
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DOI：
10.1038/srep16641
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发表时间：
2015-11-17
影响因子：
4.6
通讯作者：
Tanaka N
中科院分区：
文献类型：
--
作者：
Kusakabe Y;Ishihara M;Umeda T;Kuroda D;Nakanishi M;Kitade Y;Gouda H;Nakamura KT;Tanaka N
S-腺苷-L-同型半胱氨酸水解酶（SAH hydrolase，SAHH）是一种高度保守的酶，催化SAH可逆水解为L-同型半胱氨酸（HCY）和腺苷（ADO）。已经报道了细菌和植物SAHH的高分辨率晶体结构，但没有哺乳动物SAHH。在这里，我们报告了哺乳动物SAHH（小鼠SAHH）与反应产物（ADO）和两种反应中间体类似物-3 '-酮基-阿替霉素（3 KA）和去甲阿替霉素（NRN）-复合的第一个高分辨率晶体结构，分辨率为1.55，1.55和1.65 nm。这三种结构中的每一种都构成了SAHH水解SAH的五步过程的最后三步之一的结构快照。在NRN复合物中，作为ADO形成的必要底物的水分子在结构上首次被鉴定为通过SAHH与3 '-酮基-4'，5 '-二脱氢腺苷反应中间体的迈克尔加成中的候选供体。水分子的存在与Palmer和Abeles在1979年提出的反应机理一致。这些结果提供了对SAHH酶的反应机制的见解。
S-adenosyl-L-homocysteine hydrolase (SAH hydrolase or SAHH) is a highly conserved enzyme that catalyses the reversible hydrolysis of SAH to L-homocysteine (HCY) and adenosine (ADO). High-resolution crystal structures have been reported for bacterial and plant SAHHs, but not mammalian SAHHs. Here, we report the first high-resolution crystal structure of mammalian SAHH (mouse SAHH) in complex with a reaction product (ADO) and with two reaction intermediate analogues—3’-keto-aristeromycin (3KA) and noraristeromycin (NRN)—at resolutions of 1.55, 1.55, and 1.65 Å. Each of the three structures constitutes a structural snapshot of one of the last three steps of the five-step process of SAH hydrolysis by SAHH. In the NRN complex, a water molecule, which is an essential substrate for ADO formation, is structurally identified for the first time as the candidate donor in a Michael addition by SAHH to the 3’-keto-4’,5’-didehydroadenosine reaction intermediate. The presence of the water molecule is consistent with the reaction mechanism proposed by Palmer & Abeles in 1979. These results provide insights into the reaction mechanism of the SAHH enzyme.