Faculty of Biochemistry and Molecular Medicine, University of Oulu, Oulu, Finland.
Unit of Measurement Technology, Kajaani University Consortium, University of Oulu, Kajaani, Finland.
PLoS One. 2020 Feb 24;15(2):e0223870. doi: 10.1371/journal.pone.0223870. eCollection 2020.
Lactate oxidases belong to a group of FMN-dependent enzymes and they catalyze a conversion of lactate to pyruvate with a release of hydrogen peroxide. Hydrogen peroxide is also utilized as a read out in biosensors to quantitate lactate levels in biological samples. Aerococcus viridans lactate oxidase is the best characterized lactate oxidase and our knowledge of lactate oxidases relies largely to studies conducted with that particular enzyme. Pediococcus acidilactici lactate oxidase is also commercially available for e.g. lactate measurements, but this enzyme has not been characterized in detail before. Here we report structural characterization of the recombinant enzyme and its co-factor dependent oligomerization. The crystal structures revealed two distinct conformations in the loop closing the active site, consistent with previous biochemical studies implicating the role of loop in catalysis. Despite the structural conservation of active site residues, we were not able to detect either oxidase or monooxygenase activity when L-lactate was used as a substrate. Pediococcus acidilactici lactate oxidase is therefore an example of a misannotation of an FMN-dependent enzyme, which catalyzes likely a so far unknown oxidation reaction.
乳酸氧化酶属于黄素单核苷酸 (FMN) 依赖性酶的一组，它们催化乳酸转化为丙酮酸，并释放过氧化氢。过氧化氢也被用作生物传感器中的读出信号，以定量生物样品中的乳酸水平。发酵乳杆菌乳酸氧化酶是研究得最透彻的乳酸氧化酶，我们对乳酸氧化酶的了解主要依赖于对该特定酶的研究。例如，片球菌乳酸氧化酶也可用于乳酸测量，但是该酶以前没有详细表征过。在这里，我们报告了重组酶及其辅因子依赖性寡聚化的结构特征。晶体结构揭示了活性位点封闭环中的两种不同构象，这与先前的生化研究表明环在催化中的作用一致。尽管活性位点残基的结构保守，但当使用 L-乳酸作为底物时，我们无法检测到氧化酶或单加氧酶活性。因此，片球菌乳酸氧化酶是 FMN 依赖性酶错误注释的一个例子，它可能催化一种迄今为止未知的氧化反应。
