Is the Entner-Doudoroff pathway an overlooked glycolytic route in cyanobacteria and did cyanobacteria transfer its key enzyme via endosymbiotic gene transfer to plants?

Entner-Doudoroff 途径是蓝藻中被忽视的糖酵解途径吗？蓝藻是否通过内共生基因转移将其关键酶转移到植物中？

• 批准号: 275052541
• 负责人: Professorin Dr. Kirstin Gutekunst
• 金额: --
• 依托单位: Fachgebiet Molekulare Pflanzenphysiologie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2015
• 资助国家: 德国
• 起止时间: 2014-12-31 至 2017-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/275052541?language=en
• 关键词: Entner; Doudoroff; pathway; overlooked; glycolytic

The oxidation of glucose is central for energy metabolism throughout all domains of life. It supplies cells with ATP, reduction equivalents (NADH, NADPH) and precursors for biosynthesis. Cyanobacteria and plants are known to break down glucose either via the Embden-Meyerhoff-Parnass (EMP, often referred to as glycolysis) or the oxidative pentose phosphate (OPP) pathway. We interrupted both the EMP and OPP pathway in the cyanobacterium Synechocystis sp. PCC 6803 and found to our surprise that this mutant was still able to enhance its growth on glucose in the light. Whereas the EMP and OPP pathway are the most prevalent glycolytic routes in eukaryotes, prokaryotes display an impressive diversity in glycolytic pathways. The most prevalent are EMP, OPP and the Entner-Doudoroff (ED) pathway. We therefore searched the genome of Synechocystis for the key enzymes of the ED pathway, namely Edd (6P-gluconate dehydratase) and Eda (KDPG-aldolase) and found candidate genes for both. A knockout mutant in which the key enzymes of EMP, OPP and ED pathway and a bypass reaction of the OPP pathway were knocked out, could no longer enhance its growth on glucose. This suggests that the ED pathway might operate in Synechocystis. Labelling experiments with 13C glucose confirmed that glucose is metabolized both via the EMP and ED pathway in the light. A search for the key enzymes of both EMP (namely Pfk) and ED (namely Eda) pathway revealed that 96% of all sequenced cyanobacteria hold Eda, 58% hold both Pfk and Eda, 4% hold Pfk alone and remarkably 38% hold Eda alone. This indicates that the ED pathway might be a glycolytic route of physiological significance in cyanobacteria that has been overlooked. Remarkably Eda was also found to be widespread in plants. Phylogenetic analyses revealed that plants received this key enzyme of the ED pathway via endosymbiotic gene transfer from cyanobacteria. The physiological significance of the Enter-Doudoroff pathway as a glycolytic route in both cyanobacteria and plants is discussed.

葡萄糖的氧化是生命各个领域能量代谢的中心。它为细胞提供三磷酸腺苷、还原当量(NADH、NADPH)和生物合成前体。众所周知，蓝藻和植物通过Embden-Meyerhoff-Parnass(EMP，通常被称为糖酵解)或氧化戊糖磷酸(OPP)途径来分解葡萄糖。我们在聚球藻中阻断了EMP和OPP途径。PCC6803，并发现该突变株在光照下仍能促进其在葡萄糖上的生长。虽然EMP和OPP途径是真核生物中最常见的糖酵解途径，但原核生物的糖酵解途径表现出令人印象深刻的多样性。最常见的是EMP、OPP和Entner-Doudoroff(ED)途径。因此，我们在聚球藻基因组中寻找ED途径的关键酶，即EDD(6P-葡萄糖酸脱水酶)和EDA(KDPG-醛缩酶)，并找到了这两种酶的候选基因。EMP、OPP和ED途径的关键酶和OPP途径的旁路反应被敲除的基因敲除突变体不能再促进其在葡萄糖上的生长。这表明ED途径可能在集胞藻中起作用。~(13)C葡萄糖的标记实验证实，葡萄糖在光照下通过EMP和ED途径代谢。对EMP(即PFK)和ED(即EDA)途径关键酶的研究表明，在所有测序的蓝藻中，96%的蓝藻含有EDA，58%的蓝藻同时含有PFK和EDA，4%的蓝藻只含有PFK，38%的蓝藻只含有EDA。这表明，ED途径可能是蓝藻中一条被忽视的具有生理意义的糖酵解途径。值得注意的是，人们还发现EDA在植物中广泛存在。系统发育分析表明，植物通过蓝藻的内生共生基因转移获得了ED途径的这一关键酶。讨论了Enter-Doudoroff途径在蓝藻和植物中作为糖酵解途径的生理学意义。