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4-hydroxyphenylacetate decarboxylases: Properties of a novel subclass of glycyl radical enzyme systems

机译：4-羟基苯乙酸酯脱羧酶：糖基自由基酶系统的新亚类的性质

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The 4-hydroxyphenylacetate decarboxylases from Clostridium difficile and Clostridium scatologenes, which catalyze the formation of p-cresol, form a distinct group of glycyl radical enzymes (GREs). Cresol formation provides metabolic toxicity, which allows an active suppression of other microbes and may provide growth advantages for the producers in highly competitive environments. The GRE decarboxylases are characterized by a small subunit, which is not similar to any protein of known function in the databases, and provides unique properties that have not been observed in other GREs. Both decarboxylases are functional hetero-octamers (beta(4)gamma(4)), which contain iron-sulfur centers in addition to the glycyl radical prosthetic group. The small subunit is responsible for metal binding and is also involved in the regulation of the enzymes' oligomeric state and activity, which are triggered by reversible serine phosphorylation of the glycyl radical subunits. Biochemical data suggest that the iron-sulfur centers of the decarboxylases could be involved in the radical dissipation of previously activated enzymes in the absence of substrate. The cognate activating enzymes differ from their Pfl and Nrd counterparts in that up to two iron-sulfur centers, in addition to the characteristic SAM cluster, were found. Biochemical data suggested that these [4Fe-4S] centers are involved in the electron transfer to the SAM cluster but do not directly participate in the reductive cleavage of SAM. These data imply a tight regulation of p-cresol formation, which is necessary in order to avoid detrimental effects of the toxic product on the producers.
机译：来自艰难梭状芽胞杆菌和产臭梭菌的4-羟苯基乙酸酯脱羧酶催化对甲酚的形成，形成了不同的糖基自由基酶（GREs）组。甲酚的形成提供了代谢毒性，从而可以积极抑制其他微生物，并且可以为竞争激烈的环境中的生产者提供生长优势。 GRE脱羧酶的特征在于一个小的亚基，它与数据库中任何已知功能的蛋白质均不相似，并具有其他GRE中未观察到的独特特性。这两个脱羧酶都是功能性杂八聚物（beta（4）gamma（4）），除糖基自由基辅基外，还包含铁硫中心。小亚基负责金属结合，还参与酶的低聚状态和活性的调节，这是由糖基自由基亚基的可逆丝氨酸磷酸化触发的。生化数据表明，在没有底物的情况下，脱羧酶的铁硫中心可能参与了先前活化酶的自由基消散。同源的活化酶与它们的Pfl和Nrd对应物不同之处在于，除了特征性的SAM簇以外，还发现了多达两个铁硫中心。生化数据表明，这些[4Fe-4S]中心与电子转移至SAM团簇有关，但不直接参与SAM的还原裂解。这些数据暗示对甲酚形成的严格调控，这是避免有毒产品对生产者的有害影响所必需的。

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