Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200-135 Porto, Portugal;
Instituto de Biologia Molecular e Celular, Universidade do Porto, 4200-135 Porto, Portugal.
Proc Natl Acad Sci U S A. 2021 Oct 19;118(42). doi: 10.1073/pnas.2103803118.
Type II NADH dehydrogenases (NDH2) are monotopic enzymes present in the external or internal face of the mitochondrial inner membrane that contribute to NADH/NAD+ balance by conveying electrons from NADH to ubiquinone without coupled proton translocation. Herein, we characterize the product of a gene present in all species of the human protozoan parasite as a bona fide, matrix-oriented, type II NADH dehydrogenase. Within mitochondria, this respiratory activity concurs with that of type I NADH dehydrogenase (complex I) in some species but not others. To query the significance of NDH2 in parasite physiology, we attempted its genetic disruption in two parasite species, exhibiting a silent (, Li) and a fully operational (, Lm) complex I. Strikingly, this analysis revealed that NDH2 abrogation is not tolerated by , not even by complex I-expressing Lm species. Conversely, complex I is dispensable in both species, provided that NDH2 is sufficiently expressed. That a type II dehydrogenase is essential even in the presence of an active complex I places NADH metabolism into an entirely unique perspective and suggests unexplored functions for NDH2 that span beyond its complex I-overlapping activities. Notably, by showing that the essential character of NDH2 extends to the disease-causing stage of , we genetically validate NDH2-an enzyme without a counterpart in mammals-as a candidate target for leishmanicidal drugs.
II 型 NADH 脱氢酶（NDH2）是一种位于线粒体内膜外或内表面的单跨酶，通过将电子从 NADH 传递到泛醌而不伴有质子偶联转运，有助于 NADH/NAD+平衡。在此，我们鉴定了所有人类原生动物寄生虫物种中存在的一个基因的产物为真正的、面向基质的 II 型 NADH 脱氢酶。在线粒体中，这种呼吸活性与某些物种中的 I 型 NADH 脱氢酶（复合物 I）一致，但在其他物种中则不一致。为了研究 NDH2 在寄生虫生理学中的意义，我们尝试在两种寄生虫物种中进行其基因敲除，这两种寄生虫物种分别表现为沉默（Li）和完全功能的（Lm）复合物 I。引人注目的是，这种分析表明，即使在表达复合物 I 的 Lm 物种中，NDH2 的缺失也不能被 耐受。相反，在两种物种中，复合物 I 都是可有可无的，只要 NDH2 得到充分表达。即使存在活性复合物 I，II 型脱氢酶也是必需的，这将 NADH 代谢置于一个全新的视角，并表明 NDH2 的未被探索的功能超越了其与复合物 I 重叠的活性。值得注意的是，通过表明 NDH2 的必需性延伸到引起疾病的 阶段，我们在遗传上验证了 NDH2-一种在哺乳动物中没有对应物的酶-作为抗利什曼原虫药物的候选靶标。
