The nitroreductase superfamily of enzymes encompasses many flavin mononucleotide (FMN)-dependent catalysts promoting a wide range of reactions. All share a common core consisting of an FMN-binding domain, and individual subgroups additionally contain one to three sequence extensions radiating from defined positions within this core to support their unique catalytic properties. To identify the minimum structure required for activity in the iodotyrosine deiodinase subgroup of this superfamily, attention was directed to a representative from the thermophilic organism Thermotoga neapolitana (TnIYD). This representative was selected based on its status as an outlier of the subgroup arising from its deficiency in certain standard motifs evident in all homologues from mesophiles. We found that TnIYD lacked a typical N-terminal sequence and one of its two characteristic sequence extensions, neither of which was found to be necessary for activity. We also show that TnIYD efficiently promotes dehalogenation of iodo-, bromo-, and chlorotyrosine, analogous to related deiodinases (IYDs) from humans and other mesophiles. In addition, 2-iodophenol is a weak substrate for TnIYD as it was for all other IYDs characterized to date. Consistent with enzymes from thermophilic organisms, we observed that TnIYD adopts a compact fold and low surface area compared with IYDs from mesophilic organisms. The insights gained from our investigations on TnIYD demonstrate the advantages of focusing on sequences that diverge from conventional standards to uncover the minimum essentials for activity. We conclude that TnIYD now represents a superior starting structure for future efforts to engineer a stable dehalogenase targeting halophenols of environmental concern.

中文翻译：

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碘酪氨酸脱碘酶功能的最小结构是由来自嗜热细菌那不勒斯栖热袍菌的异常蛋白定义的。

硝基还原酶超家族包含许多黄素单核苷酸 (FMN) 依赖性催化剂，可促进多种反应。所有这些都共享一个由 FMN 结合结构域组成的共同核心，并且各个亚组还包含从该核心内的定义位置辐射的一到三个序列延伸，以支持其独特的催化特性。为了确定该超家族的碘酪氨酸脱碘酶亚组活性所需的最小结构，我们将注意力集中在嗜热生物那不勒斯栖热袍菌 (TnIYD) 的代表身上。该代表的选择是基于其作为该亚组的异常值的地位，这是由于其缺乏某些标准基序，这些标准基序在嗜温生物的所有同系物中都很明显。我们发现 TnIYD 缺乏典型的 N 端序列及其两个特征序列延伸之一，但发现这两个序列都不是活性所必需的。我们还表明，TnIYD 有效促进碘、溴和氯酪氨酸的脱卤，类似于人类和其他嗜温生物的相关脱碘酶 (IYD)。此外，2-碘苯酚是 TnIYD 的弱底物，就像迄今为止表征的所有其他 IYD 一样。与来自嗜热生物的酶一致，我们观察到与来自嗜温生物的 IYD 相比，TnIYD 采用紧凑的折叠和低表面积。我们从 TnIYD 调查中获得的见解证明了关注与传统标准不同的序列以揭示活动的最低要素的优势。我们得出的结论是，TnIYD 现在代表了未来设计针对环境问题的卤代酚的稳定脱卤酶的卓越起始结构。