Omini Joy, Krassovskaya Inga, Dele-Osibanjo Taiwo, Pedersen Connor, Obata Toshihiro
Department of Biochemistry and Center for Plant Science Innovation, University of Nebraska-Lincoln, 1901 Vine Street, Lincoln, Nebraska 68588, USA.
bioRxiv. 2025 Jun 20:2025.06.16.659985. doi: 10.1101/2025.06.16.659985.
The tricarboxylic acid (TCA) cycle enzymes, malate dehydrogenase (MDH1) and citrate synthase (CIT1), form a multienzyme complex called 'metabolon' that channels intermediate, oxaloacetate, between the reaction centers of the enzymes. Since the MDH1-CIT1 metabolon enhances the pathway reactions in vitro, it is postulated to regulate the TCA cycle flux through dynamic assembly in response to cellular metabolic demands. Here, we demonstrated that yeast mitochondrial MDH1 and CIT1 dissociated when aerobic respiration was suppressed by the Crabtree effect and associated when the pathway flux was enhanced by acetate. Pharmacological TCA cycle inhibitions dissociated the complex, while electron transport chain inhibition enhanced the interaction. The multienzyme complex assembly was related to the mitochondrial matrix acidification and oxidation, as well as cellular levels of malate, fumarate, and citrate. These factors significantly affected the MDH1-CIT1 complex affinity in vitro. Especially the buffer pH significantly changed the MDH1-CIT1 affinity within the pH range between 6.0 and 7.0, which is observed in the mitochondrial matrix under physiological conditions. These results show a dynamic association and dissociation of a metabolon in the mitochondria and its relationship with pathway flux, supporting the metabolon's role in metabolic regulation. Multiple factors, including pH and metabolite availabilities, possibly regulate MDH1-CIT1 interaction.
三羧酸(TCA)循环酶,苹果酸脱氢酶(MDH1)和柠檬酸合酶(CIT1),形成一种称为“代谢体”的多酶复合物,该复合物可在酶的反应中心之间传递中间体草酰乙酸。由于MDH1-CIT1代谢体在体外增强了途径反应,因此推测它可通过动态组装来响应细胞代谢需求,从而调节TCA循环通量。在这里,我们证明了酵母线粒体MDH1和CIT1在有氧呼吸被克氏效应抑制时会解离,而当途径通量因乙酸盐而增强时会结合。药理学上的TCA循环抑制会使复合物解离,而电子传递链抑制会增强相互作用。多酶复合物的组装与线粒体基质的酸化和氧化以及苹果酸、富马酸和柠檬酸的细胞水平有关。这些因素在体外显著影响MDH1-CIT1复合物的亲和力。特别是缓冲液pH在6.0至7.0的范围内显著改变了MDH1-CIT1的亲和力,这在生理条件下的线粒体基质中也能观察到。这些结果表明线粒体中代谢体的动态结合和解离及其与途径通量的关系,支持了代谢体在代谢调节中的作用。包括pH和代谢物可用性在内的多种因素可能调节MDH1-CIT1的相互作用。