The Commonwealth Scientific and Industrial Research Organization Materials, Science and Engineering, Parkville, Victoria 3052, Australia.
Plant Cell. 2012 Nov;24(11):4525-38. doi: 10.1105/tpc.112.102921. Epub 2012 Nov 6.
Auxins are important for plant growth and development, including the control of fruit ripening. Conjugation to amino acids by indole-3-acetic acid (IAA)-amido synthetases is an important part of auxin homeostasis. The structure of the auxin-conjugating Gretchen Hagen3-1 (GH3-1) enzyme from grapevine (Vitis vinifera), in complex with an inhibitor (adenosine-5'-[2-(1H-indol-3-yl)ethyl]phosphate), is presented. Comparison with a previously published benzoate-conjugating enzyme from Arabidopsis thaliana indicates that grapevine GH3-1 has a highly similar domain structure and also undergoes a large conformational change during catalysis. Mutational analyses and structural comparisons with other proteins have identified residues likely to be involved in acyl group, amino acid, and ATP substrate binding. Vv GH3-1 is a monomer in solution and requires magnesium ions solely for the adenlyation reaction. Modeling of IAA and two synthetic auxins, benzothiazole-2-oxyacetic acid (BTOA) and 1-naphthaleneacetic acid (NAA), into the active site indicates that NAA and BTOA are likely to be poor substrates for this enzyme, confirming previous enzyme kinetic studies. This suggests a reason for the increased effectiveness of NAA and BTOA as auxins in planta and provides a tool for designing new and effective auxins.
植物生长素对于植物的生长和发育非常重要，包括控制果实成熟。吲哚-3-乙酸（IAA）-酰胺合成酶将生长素与氨基酸结合，是生长素动态平衡的重要组成部分。葡萄（Vitis vinifera）中生长素结合酶 Gretchen Hagen3-1（GH3-1）与抑制剂（腺苷-5'-[2-（1H-吲哚-3-基）乙基]磷酸）的复合物结构已被确定。与之前发表的拟南芥苯甲酸结合酶的比较表明，葡萄 GH3-1 具有高度相似的结构域结构，并且在催化过程中也经历了很大的构象变化。突变分析和与其他蛋白质的结构比较确定了可能参与酰基、氨基酸和 ATP 底物结合的残基。Vv GH3-1 在溶液中是单体，仅需要镁离子进行腺苷酰化反应。将 IAA 和两种合成生长素，苯并噻唑-2-氧乙酸（BTOA）和 1-萘乙酸（NAA），模拟到活性位点表明，NAA 和 BTOA 可能是该酶的不良底物，这证实了之前的酶动力学研究。这为 NAA 和 BTOA 在植物中作为生长素的有效性增加提供了一个原因，并为设计新的有效生长素提供了一个工具。
