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Aurone synthase is a catechol oxidase with hydroxylase activity and provides insights into the mechanism of plant polyphenol oxidases

机译：Aurone合酶是一种具有羟化酶活性的邻苯二酚氧化酶，可深入了解植物多酚氧化酶的机制

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Tyrosinases and catechol oxidases belong to the family of polyphenol oxidases (PPOs). Tyrosinases catalyze the o-hydroxylation and oxidation of phenolic compounds, whereas catechol oxidases were so far defined to lack the hydroxylation activity and catalyze solely the oxidation of o-diphenolic compounds. Aurone synthase from Coreopsis grandiflora (AUS1) is a specialized plant PPO involved in the anabolic pathway of aurones. We present, to our knowledge, the first crystal structures of a latent plant PPO, its mature active and inactive form, caused by a sulfation of a copper binding histidine. Analysis of the latent proenzyme’s interface between the shielding C-terminal domain and the main core provides insights into its activation mechanisms. As AUS1 did not accept common tyrosinase substrates (tyrosine and tyramine), the enzyme is classified as a catechol oxidase. However, AUS1 showed hydroxylase activity toward its natural substrate (isoliquiritigenin), revealing that the hydroxylase activity is not correlated with the acceptance of common tyrosinase substrates. Therefore, we propose that the hydroxylase reaction is a general functionality of PPOs. Molecular dynamics simulations of docked substrate–enzyme complexes were performed, and a key residue was identified that influences the plant PPO’s acceptance or rejection of tyramine. Based on the evidenced hydroxylase activity and the interactions of specific residues with the substrates during the molecular dynamics simulations, a novel catalytic reaction mechanism for plant PPOs is proposed. The presented results strongly suggest that the physiological role of plant catechol oxidases were previously underestimated, as they might hydroxylate their—so far unknown—natural substrates in vivo
机译：酪氨酸酶和儿茶酚氧化酶属于多酚氧化酶（PPO）家族。酪氨酸酶催化酚类化合物的邻羟基化和氧化，而到目前为止，儿茶酚氧化酶被定义为缺乏羟基化活性而仅催化邻二酚类化合物的氧化。大花金鸡油（AUS1）的Aurone合酶是一种专门的植物PPO，参与了Auroone的合成代谢途径。据我们所知，我们提出了一种潜在植物PPO的第一个晶体结构，其成熟的活性和非活性形式，是由结合铜的组氨酸的硫酸化引起的。通过分析屏蔽C末端结构域和主要核心之间潜在酶的界面，可以深入了解其激活机制。由于AUS1不接受常见的酪氨酸酶底物（酪氨酸和酪胺），因此该酶被归类为儿茶酚氧化酶。但是，AUS1对它的天然底物（isoliquiritigenin）表现出羟化酶活性，这表明羟化酶活性与普通酪氨酸酶底物的接受程度无关。因此，我们建议羟化酶反应是PPO的一般功能。进行了对接的底物-酶复合物的分子动力学模拟，并确定了影响植物PPO对酪胺的接受或排斥的关键残基。基于分子动力学模拟中羟化酶的活性以及特定残基与底物的相互作用，提出了一种新的植物PPO催化反应机理。提出的结果强烈表明，植物邻苯二酚氧化酶的生理作用先前被低估了，因为它们可能在体内将其迄今未知的天然底物羟化

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