The bacterium Pseudomonas sp. AP-3 is able to use the environmental pollutant 2-aminophenol as its sole source of carbon, nitrogen, and energy. Eight genes (amnA, B, C, D, E, F, G, and H) encoding 2-aminophenol metabolizing enzymes are clustered into a single operon. 2-Aminomuconic 6-semialdehyde dehydrogenase (AmnC), a member of the aldehyde dehydrogenase (ALDH) superfamily, is responsible for oxidizing 2-aminomuconic 6-semialdehyde to 2-aminomuconate. In contrast to many other members of the ALDH superfamily, the structural basis of the catalytic activity of AmnC remains elusive. Here, we present the crystal structure of AmnC, which displays a homotetrameric quaternary assembly that is directly involved in its enzymatic activity. The tetrameric state of AmnC in solution was also presented using small-angle X-ray scattering. The tetramerization of AmnC is mediated by the assembly of a protruding hydrophobic beta-strand motif and residues V121 and S123 located in the NAD⁺-binding domain of each subunit. Dimeric mutants of AmnC dramatically lose NAD⁺ binding affinity and failed to oxidize the substrate analogue 2-hydroxymuconate-6-semialdehyde to α-hydroxymuconic acid, indicating that tetrameric assembly of AmnC is functional requirement.

中文翻译：

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2-氨基粘康6-半醛脱氢酶的四聚体组装是辅因子NAD+结合的功能要求

细菌假单胞菌属。AP-3能够使用环境污染物 2-氨基苯酚作为其唯一的碳、氮和能源来源。编码 2-氨基苯酚代谢酶的八个基因（amnA、B、C、D、E、F、G 和 H）聚集成一个操纵子。2-氨基粘康6-半醛脱氢酶 (AmnC) 是醛脱氢酶 (ALDH) 超家族的成员，负责将 2-氨基粘康 6-半醛氧化为 2-氨基粘康酸。与 ALDH 超家族的许多其他成员相比，AmnC 催化活性的结构基础仍然难以捉摸。在这里，我们展示了 AmnC 的晶体结构，它显示了一个直接参与其酶活性的同型四聚体四元组装。还使用小角 X 射线散射呈现了溶液中 AmnC 的四聚体状态。⁺每个亚基的结合域。AmnC 的二聚体突变体显着失去了 NAD ⁺结合亲和力，并且未能将底物类似物 2-羟基粘康酸盐-6-半醛氧化为 α-羟基粘康酸，表明 AmnC 的四聚体组装是功能要求。