Wang Kai-Tuo, Wang Juan, Li Lan-Fen, Su Xiao-Dong
National Laboratory of Protein Engineering and Plant Genetic Engineering, College of Life Sciences, Peking University, Beijing, P.R. China.
J Mol Biol. 2009 Jul 24;390(4):747-59. doi: 10.1016/j.jmb.2009.05.032. Epub 2009 May 25.
Selenophosphate synthetase catalyzes the synthesis of the highly active selenium donor molecule selenophosphate, a key intermediate in selenium metabolism. We have determined the high-resolution crystal structure of human selenophosphate synthetase 1 (hSPS1). An unexpected reaction intermediate, with a tightly bound phosphate and ADP at the active site has been captured in the structure. An enzymatic assay revealed that hSPS1 possesses low ADP hydrolysis activity in the presence of phosphate. Our structural and enzymatic results suggest that consuming the second high-energy phosphoester bond of ATP could protect the labile product selenophosphate during catalytic reaction. We solved another hSPS1 structure with potassium ions at the active sites. Comparing the two structures, we were able to define the monovalent cation-binding site of the enzyme. The detailed mechanism of the ADP hydrolysis step and the exact function of the monovalent cation for hSPS1 catalytic reaction are proposed.
硒磷酸合成酶催化高活性硒供体分子硒磷酸的合成，硒磷酸是硒代谢中的关键中间体。我们已经确定了人硒磷酸合成酶1（hSPS1）的高分辨率晶体结构。在该结构中捕获到了一种意外的反应中间体，其活性位点处紧密结合有磷酸盐和ADP。酶活性测定表明，在磷酸盐存在的情况下，hSPS1具有较低的ADP水解活性。我们的结构和酶学结果表明，消耗ATP的第二个高能磷酸酯键可以在催化反应过程中保护不稳定的产物硒磷酸。我们解析了活性位点带有钾离子的另一种hSPS1结构。比较这两种结构，我们能够确定该酶的单价阳离子结合位点。提出了ADP水解步骤的详细机制以及单价阳离子对hSPS1催化反应的确切功能。
