Department of Microbiology, University of Georgia, Athens, Georgia, USA.
Department of Microbiology, University of Georgia, Athens, Georgia, USA
mBio. 2018 Feb 27;9(1):e00084-18. doi: 10.1128/mBio.00084-18.
A variety of metabolic deficiencies and human diseases arise from the disruption of mitochondrial enzymes and/or loss of mitochondrial DNA. Mounting evidence shows that eukaryotes have conserved enzymes that prevent the accumulation of reactive metabolites that cause stress inside the mitochondrion. 2-Aminoacrylate is a reactive enamine generated by pyridoxal 5'-phosphate-dependent α,β-eliminases as an obligatory intermediate in the breakdown of serine. In prokaryotes, members of the broadly conserved RidA family (PF14588) prevent metabolic stress by deaminating 2-aminoacrylate to pyruvate. Here, we demonstrate that unmanaged 2-aminoacrylate accumulation in mitochondria causes transient metabolic stress and the irreversible loss of mitochondrial DNA. The RidA family protein Mmf1p deaminates 2-aminoacrylate, preempting metabolic stress and loss of the mitochondrial genome. Disruption of the mitochondrial pyridoxal 5'-phosphate-dependent serine dehydratases (Ilv1p and Cha1p) prevents 2-aminoacrylate formation, avoiding stress in the absence of Mmf1p. Furthermore, chelation of iron in the growth medium improves maintenance of the mitochondrial genome in yeast challenged with 2-aminoacrylate, suggesting that 2-aminoacrylate-dependent loss of mitochondrial DNA is influenced by disruption of iron homeostasis. Taken together, the data indicate that Mmf1p indirectly contributes to mitochondrial DNA maintenance by preventing 2-aminoacrylate stress derived from mitochondrial amino acid metabolism. Deleterious reactive metabolites are produced as a consequence of many intracellular biochemical transformations. Importantly, reactive metabolites that appear short-lived have the potential to persist within intracellular environments, leading to pervasive cell damage and diminished fitness. To overcome metabolite damage, organisms utilize enzymatic reactive-metabolite defense systems to rid the cell of deleterious metabolites. In this report, we describe the importance of the RidA/YER057c/UK114 enamine/imine deaminase family in preventing 2-aminoacrylate stress in yeast. lacking the enamine/imine deaminase Mmf1p was shown to experience pleiotropic growth defects and fails to maintain its mitochondrial genome. Our results provide the first line of evidence that uncontrolled 2-aminoacrylate stress derived from mitochondrial serine metabolism can negatively impact mitochondrial DNA maintenance in eukaryotes.
各种代谢缺陷和人类疾病都是由于线粒体酶的破坏和/或线粒体 DNA 的丢失引起的。越来越多的证据表明，真核生物具有保守的酶，可以防止引起线粒体内部应激的反应性代谢物的积累。2-氨基丙烯酸是一种反应性烯胺，由吡哆醛 5'-磷酸依赖性α，β-消除酶作为丝氨酸分解的必需中间体生成。在原核生物中，广泛保守的 RidA 家族（PF14588）成员通过将 2-氨基丙烯酸脱氨为丙酮酸来防止代谢应激。在这里，我们证明线粒体中未被管理的 2-氨基丙烯酸积累会导致短暂的代谢应激和线粒体 DNA 的不可逆损失。RidA 家族蛋白 Mmf1p 将 2-氨基丙烯酸脱氨，先发制人地防止代谢应激和线粒体基因组的丢失。破坏线粒体吡哆醛 5'-磷酸依赖性丝氨酸脱水酶（Ilv1p 和 Cha1p）可防止 2-氨基丙烯酸的形成，从而避免在没有 Mmf1p 的情况下出现应激。此外，在生长培养基中螯合铁可以改善酵母在受到 2-氨基丙烯酸挑战时对线粒体基因组的维持，这表明铁稳态的破坏会影响 2-氨基丙烯酸依赖性线粒体 DNA 的丢失。总的来说，数据表明 Mmf1p 通过防止源自线粒体氨基酸代谢的 2-氨基丙烯酸应激间接有助于线粒体 DNA 的维持。有害的反应性代谢物是许多细胞内生化转化的结果。重要的是，看起来寿命短的反应性代谢物有可能在细胞内环境中持续存在，导致广泛的细胞损伤和适应性降低。为了克服代谢物损伤，生物体利用酶促反应性代谢物防御系统清除细胞中的有害代谢物。在本报告中，我们描述了 RidA/YER057c/UK114 烯胺/亚胺脱氨酶家族在防止酵母中 2-氨基丙烯酸应激中的重要性。缺乏烯胺/亚胺脱氨酶 Mmf1p 的酵母表现出多种生长缺陷，并且无法维持其线粒体基因组。我们的结果首次提供了证据，证明源自线粒体丝氨酸代谢的不受控制的 2-氨基丙烯酸应激可能会对真核生物中线粒体 DNA 的维持产生负面影响。
