Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama-cho, Ikoma, Nara 630-0192, Japan.
Graduate School of Human Development and Environment, Kobe University, 3-11 Tsurukabuto, Nada-Ku, Kobe 657-8501, Japan.
Nat Commun. 2017 Jan 13;8:14007. doi: 10.1038/ncomms14007.
Two enzymes are considered to be unique to the photosynthetic Calvin-Benson cycle: ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), responsible for CO fixation, and phosphoribulokinase (PRK). Some archaea possess bona fide RuBisCOs, despite not being photosynthetic organisms, but are thought to lack PRK. Here we demonstrate the existence in methanogenic archaea of a carbon metabolic pathway involving RuBisCO and PRK, which we term 'reductive hexulose-phosphate' (RHP) pathway. These archaea possess both RuBisCO and a catalytically active PRK whose crystal structure resembles that of photosynthetic bacterial PRK. Capillary electrophoresis-mass spectrometric analysis of metabolites reveals that the RHP pathway, which differs from the Calvin-Benson cycle only in a few steps, is active in vivo. Our work highlights evolutionary and functional links between RuBisCO-mediated carbon metabolic pathways in methanogenic archaea and photosynthetic organisms. Whether the RHP pathway allows for autotrophy (that is, growth exclusively with CO as carbon source) remains unknown.
两种酶被认为是光合作用卡尔文-本森循环所特有的：核酮糖-1,5-二磷酸羧化酶/加氧酶（RuBisCO），负责 CO 固定，以及磷酸核酮糖激酶（PRK）。尽管一些古菌不是光合生物，但它们拥有真正的 RuBisCO，却被认为缺乏 PRK。在这里，我们证明了参与 RuBisCO 和 PRK 的碳代谢途径存在于产甲烷古菌中，我们将其称为“还原性己糖磷酸”（RHP）途径。这些古菌既拥有 RuBisCO，又拥有具有催化活性的 PRK，其晶体结构类似于光合细菌 PRK。代谢产物的毛细管电泳-质谱分析表明，RHP 途径与卡尔文-本森循环仅在几个步骤上有所不同，在体内是活跃的。我们的工作强调了产甲烷古菌中 RuBisCO 介导的碳代谢途径与光合生物之间的进化和功能联系。RHP 途径是否允许自养（即仅以 CO 作为碳源进行生长）仍不清楚。
