School of Biological and Biomedical Sciences, Durham University, Durham DH1 3LE, United Kingdom.
J Biol Chem. 2012 Feb 3;287(6):4023-32. doi: 10.1074/jbc.M111.314450. Epub 2011 Dec 8.
Plant resistance proteins (R-proteins) are key components of the plant immune system activated in response to a plethora of different pathogens. R-proteins are P-loop NTPase superfamily members, and current models describe their main function as ATPases in defense signaling pathways. Here we show that a subset of R-proteins have evolved a new function to combat pathogen infection. This subset of R-proteins possesses a nucleotide phosphatase activity in the nucleotide-binding domain. Related R-proteins that fall in the same phylogenetic clade all show the same nucleotide phosphatase activity indicating a conserved function within at least a subset of R-proteins. R-protein nucleotide phosphatases catalyze the production of nucleoside from nucleotide with the nucleotide monophosphate as the preferred substrate. Mutation of conserved catalytic residues substantially reduced activity consistent with the biochemistry of P-loop NTPases. Kinetic analysis, analytical gel filtration, and chemical cross-linking demonstrated that the nucleotide-binding domain was active as a multimer. Nuclear magnetic resonance and nucleotide analogues identified the terminal phosphate bond as the target of a reaction that utilized a metal-mediated nucleophilic attack by water on the phosphoester. In conclusion, we have identified a group of R-proteins with a unique function. This biochemical activity appears to have co-evolved with plants in signaling pathways designed to resist pathogen attack.
植物抗性蛋白（R 蛋白）是植物免疫系统的关键组成部分，可被激活以响应多种不同的病原体。R 蛋白是 P 环 NTPase 超家族成员，目前的模型将其主要功能描述为防御信号通路中的 ATP 酶。在这里，我们展示了一组 R 蛋白已经进化出一种新的功能来对抗病原体感染。这组 R 蛋白在核苷酸结合域中具有核苷酸磷酸酶活性。属于同一系统发育分支的相关 R 蛋白均显示出相同的核苷酸磷酸酶活性，表明至少在 R 蛋白的一个亚组中存在保守功能。R 蛋白核苷酸磷酸酶催化核苷酸产生核苷，核苷酸单磷酸是首选底物。保守催化残基的突变大大降低了活性，这与 P 环 NTPase 的生物化学一致。动力学分析、分析凝胶过滤和化学交联表明，核苷酸结合域作为多聚体发挥活性。核磁共振和核苷酸类似物确定了末端磷酸键是反应的靶标，该反应利用金属介导的亲核攻击水对磷酸酯的反应。总之，我们已经确定了一组具有独特功能的 R 蛋白。这种生化活性似乎与植物在设计用于抵抗病原体攻击的信号通路中共同进化。
