Structural insight into the reaction mechanism and evolution of cytokinin biosynthesis
Structural insight into the reaction mechanism and evolution of cytokinin biosynthesis
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DOI：
10.1073/pnas.0707374105
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发表时间：
2008-02-19
影响因子：
11.1
通讯作者：
Sakakibara, Hitoshi
中科院分区：
文献类型：
--
作者：
Sugawara, Hajime;Ueda, Nanae;Sakakibara, Hitoshi
植物激素细胞分裂素调节植物的生长和发育。这种激素也由一些植物病原细菌如根癌农杆菌合成，并且是植物肿瘤形成的关键因素。细胞分裂素生物合成的限速步骤由磷酸腺苷异戊烯基转移酶（IPT）催化。农杆菌IPT具有独特的底物特异性，使其能够通过募集宿主植物生物合成途径的代谢中间体来增加反式玉米素的产量。在这里，我们显示了Tzs的晶体结构，一个来自A的IPT。tumiefaciens，与AMP和异戊二烯基供体类似物，二甲基烯丙基S-硫代二磷酸复合。结构表明，碳-氮基异戊二烯化反应是通过SN 2-反应机理进行的。定点诱变用于确定氨基酸残基，Asp-173和His-214，这是负责异戊烯基-克隆底物特异性之间的差异，植物和细菌的IPT。IPT和含p环的核苷三磷酸水解酶可能从共同的祖先蛋白进化而来。尽管结构相似，IPT已经进化出一种独特的作用，其中p环转移细胞分裂素生物合成中的异戊二烯基部分。
The phytohormone cytokinin regulates plant growth and development. This hormone is also synthesized by some phytopathogenic bacteria, such as Agrobacterium tumefaciens, and is as a key factor in the formation of plant tumors. The rate-limiting step of cytokinin biosynthesis is catalyzed by adenosine phosphate-isopentenyltransferase (IPT). Agrobacterium IPT has a unique substrate specificity that enables it to increase trans-zeatin production by recruiting a metabolic intermediate of the host plant's biosynthetic pathway. Here, we show the crystal structures of Tzs, an IPT from A. tumiefaciens, complexed with AMP and a prenyl-donor analogue, dimethylallyl S-thiodiphosphate. The structures reveal that the carbon-nitrogen-based prenylation proceeds by the SN2-reaction mechanism. Site-directed mutagenesis was used to determine the amino acid residues, Asp-173 and His-214, which are responsible for differences in prenyl-clonor substrate specificity between plant and bacterial IPTs. IPT and the p loop-containing nucleoside triphosphate hydrolases likely evolved from a common ancestral protein. Despite structural similarities, IPT has evolved a distinct role in which the p loop transfers a prenyl moiety in cytokinin biosynthesis.