Chu Hsing-Mao, Guo Rey-Ting, Lin Ting-Wan, Chou Chia-Cheng, Shr Hui-Lin, Lai Hui-Lin, Tang Tsung-Yin, Cheng Kuo-Joan, Selinger Brent L, Wang Andrew H-J
Institute of Biochemical Sciences, National Taiwan University, Taipei 106, Taiwan.
Structure. 2004 Nov;12(11):2015-24. doi: 10.1016/j.str.2004.08.010.
Various inositide phosphatases participate in the regulation of inositol polyphosphate signaling molecules. Plant phytases are phosphatases that hydrolyze phytate to less-phosphorylated myo-inositol derivatives and phosphate. The phytase from Selenomonas ruminantium shares no sequence homology with other microbial phytases. Its crystal structure revealed a phytase fold of the dual-specificity phosphatase type. The active site is located near a conserved cysteine-containing (Cys241) P loop. We also solved two other crystal forms in which an inhibitor, myo-inositol hexasulfate, is cocrystallized with the enzyme. In the "standby" and the "inhibited" crystal forms, the inhibitor is bound, respectively, in a pocket slightly away from Cys241 and at the substrate binding site where the phosphate group to be hydrolyzed is held close to the -SH group of Cys241. Our structural and mutagenesis studies allow us to visualize the way in which the P loop-containing phytase attracts and hydrolyzes the substrate (phytate) sequentially.
多种肌醇磷酸酶参与肌醇多磷酸信号分子的调控。植物植酸酶是一种将植酸水解为磷酸化程度较低的肌醇衍生物和磷酸的磷酸酶。来自反刍月形单胞菌的植酸酶与其他微生物植酸酶没有序列同源性。其晶体结构显示为双特异性磷酸酶类型的植酸酶折叠。活性位点位于一个保守的含半胱氨酸（Cys241）的P环附近。我们还解析了另外两种晶体形式，其中一种抑制剂——肌醇六硫酸盐与该酶共结晶。在“备用”和“抑制”晶体形式中，抑制剂分别结合在一个略远离Cys241的口袋中以及底物结合位点，在底物结合位点处待水解的磷酸基团靠近Cys241的 -SH基团。我们的结构和诱变研究使我们能够直观地看到含P环的植酸酶依次吸引和水解底物（植酸）的方式。
