Pflanzenphysiologie, Fachbereich Biologie, Universität Kaiserslautern, Erwin-Schrödinger-Strasse, D-67663, Kaiserslautern, Germany.
Instituto de Biomedicina de Valencia (IBV-CSIC), Jaime Roig 11, 46010, Valencia, Spain.
Nat Commun. 2021 Feb 11;12(1):947. doi: 10.1038/s41467-021-21165-9.
Aspartate transcarbamoylase (ATC), an essential enzyme for de novo pyrimidine biosynthesis, is uniquely regulated in plants by feedback inhibition of uridine 5-monophosphate (UMP). Despite its importance in plant growth, the structure of this UMP-controlled ATC and the regulatory mechanism remain unknown. Here, we report the crystal structures of Arabidopsis ATC trimer free and bound to UMP, complexed to a transition-state analog or bearing a mutation that turns the enzyme insensitive to UMP. We found that UMP binds and blocks the ATC active site, directly competing with the binding of the substrates. We also prove that UMP recognition relies on a loop exclusively conserved in plants that is also responsible for the sequential firing of the active sites. In this work, we describe unique regulatory and catalytic properties of plant ATCs that could be exploited to modulate de novo pyrimidine synthesis and plant growth.
天冬氨酸转氨甲酰酶（ATC）是从头嘧啶生物合成所必需的酶，其在植物中通过尿苷 5-单磷酸（UMP）的反馈抑制而被独特地调节。尽管它对植物生长很重要，但这种 UMP 控制的 ATC 的结构和调节机制仍然未知。在这里，我们报告了游离态和与 UMP 结合的拟南芥 ATC 三聚体、与过渡态类似物结合的或带有使酶对 UMP 不敏感的突变的结构。我们发现 UMP 结合并阻断 ATC 活性部位，直接与底物的结合竞争。我们还证明 UMP 的识别依赖于一个仅在植物中保守的环，该环也负责活性部位的顺序点火。在这项工作中，我们描述了植物 ATC 的独特的调节和催化特性，这些特性可被用来调节从头嘧啶合成和植物生长。
