Acetohydroxyacid synthase (AHAS), also known as acetolactate synthase, is a flavin adenine dinucleotide-, thiamine diphosphate- and magnesium-dependent enzyme that catalyses the first step in the biosynthesis of branched-chain amino acids 1 . It is the target for more than 50 commercial herbicides 2 . AHAS requires both catalytic and regulatory subunits for maximal activity and functionality. Here we describe structures of the hexadecameric AHAS complexes of Saccharomyces cerevisiae and dodecameric AHAS complexes of Arabidopsis thaliana . We found that the regulatory subunits of these AHAS complexes form a core to which the catalytic subunit dimers are attached, adopting the shape of a Maltese cross. The structures show how the catalytic and regulatory subunits communicate with each other to provide a pathway for activation and for feedback inhibition by branched-chain amino acids. We also show that the AHAS complex of Mycobacterium tuberculosis adopts a similar structure, thus demonstrating that the overall AHAS architecture is conserved across kingdoms. Structures of the acetohydroxyacid synthase complexes of Saccharomyces cerevisiae and Arabidopsis thaliana provide insights into the biosynthesis of and feedback inhibition by branched-chain amino acids.

中文翻译：

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真菌和植物乙酰羟酸合酶的结构

乙酰羟酸合酶 (AHAS)，也称为乙酰乳酸合酶，是一种黄素腺嘌呤二核苷酸、硫胺二磷酸和镁依赖性酶，可催化支链氨基酸 1 生物合成的第一步。它是 50 多种商业除草剂 2 的目标。AHAS 需要催化亚基和调节亚基才能发挥最大的活性和功能。在这里，我们描述了酿酒酵母的十六聚 AHAS 复合物和拟南芥的十二聚 AHAS 复合物的结构。我们发现这些 AHAS 复合物的调节亚基形成一个核心，催化亚基二聚体附着在该核心上，采用马耳他十字的形状。这些结构显示了催化亚基和调节亚基如何相互通信，从而为支链氨基酸的激活和反馈抑制提供途径。我们还表明结核分枝杆菌的 AHAS 复合体采用相似的结构，从而证明整个 AHAS 结构在跨界是保守的。酿酒酵母和拟南芥的乙酰羟酸合酶复合物的结构提供了对支链氨基酸的生物合成和反馈抑制的见解。