School of Life Science and Technology, Tokyo Institute of Technology, 4259-B7, Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan.
J Biochem. 2023 Oct 31;174(5):441-450. doi: 10.1093/jb/mvad062.
Quinonoid dihydropteridine reductase (QDPR) catalyses the reduction of quinonoid-form dihydrobiopterin (qBH2) to tetrahydrobiopterin (BH4). BH4 metabolism is a drug target for neglected tropical disorders because trypanosomatid protozoans, including Leishmania and Trypanosoma, require exogenous sources of biopterin for growth. Although QDPR is a key enzyme for maintaining intracellular BH4 levels, the precise catalytic properties and reaction mechanisms of QDPR are poorly understood due to the instability of quinonoid-form substrates. In this study, we analysed the binding profile of qBH2 to human QDPR in combination with in silico and in vitro methods. First, we performed docking simulation of qBH2 to QDPR to obtain possible binding modes of qBH2 at the active site of QDPR. Then, among them, we determined the most plausible binding mode using molecular dynamics simulations revealing its atomic-level interactions and confirmed it with the in vitro assay of mutant enzymes. Moreover, it was found that not only qBH2 but also quinonoid-form dihydrofolate (qDHF) could be potential physiological substrates for QDPR, suggesting that QDPR may be a bifunctional enzyme. These findings in this study provide important insights into biopterin and folate metabolism and would be useful for developing drugs for neglected tropical diseases.
醌型二氢蝶啶还原酶（QDPR）催化醌型二氢生物蝶呤（qBH2）还原为四氢生物蝶呤（BH4）。BH4 代谢是治疗被忽视热带病的药物靶点，因为包括利什曼原虫和锥虫在内的原生动物需要外源生物蝶呤来生长。尽管 QDPR 是维持细胞内 BH4 水平的关键酶，但由于醌型底物的不稳定性，QDPR 的精确催化特性和反应机制仍不清楚。在这项研究中，我们结合了计算机模拟和体外方法，分析了 qBH2 与人类 QDPR 的结合特征。首先，我们对 QDPR 进行了 qBH2 的对接模拟，以获得 qBH2 在 QDPR 活性部位的可能结合模式。然后，我们通过分子动力学模拟确定了最合理的结合模式，揭示了其原子水平的相互作用，并通过突变酶的体外测定进行了验证。此外，研究还发现，不仅 qBH2，而且醌型二氢叶酸（qDHF）也可能是 QDPR 的潜在生理底物，这表明 QDPR 可能是一种双功能酶。本研究的这些发现为生物蝶呤和叶酸代谢提供了重要的见解，并将有助于开发治疗被忽视热带病的药物。
