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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Structural insight into the reaction mechanism and evolution of cytokinin biosynthesis
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Structural insight into the reaction mechanism and evolution of cytokinin biosynthesis

机译：对细胞分裂素生物合成反应机理和演化的结构见解

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摘要

The phytohormone cytokinin regulates plant growth and development. This hormone is also synthesized by some phytopatho-genic 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 biosyn-thetic pathway. Here, we show the crystal structures of Tzs, an IPT from A. tumefaciens, 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-donor 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.
机译：植物激素细胞分裂素调节植物的生长和发育。这种激素还可以通过某些植物病原细菌（例如根癌农杆菌）合成，并且是形成植物肿瘤的关键因素。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玉米素的产量。在这里，我们显示Tzs的晶体结构，一种来自根癌农杆菌的IPT，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。该结构表明，基于碳氮的烯丙基化是通过SN2反应机理进行的。使用定点诱变来确定氨基酸残基Asp-173和His-214，这是造成植物和细菌IPT之间异戊二烯供体底物特异性差异的原因。 IPT和含p环的核苷三磷酸水解酶可能是从共同的祖先蛋白进化而来的。尽管在结构上有相似之处，但IPT发挥了独特的作用，其中p环在细胞分裂素生物合成中转移异戊二烯基部分。

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