Glycolytic Shunts Replenish the Calvin-Benson-Bassham Cycle as Anaplerotic Reactions in Cyanobacteria
Glycolytic Shunts Replenish the Calvin-Benson-Bassham Cycle as Anaplerotic Reactions in Cyanobacteria
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DOI：
10.1016/j.molp.2020.02.002
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发表时间：
2020-03-02
期刊：
影响因子：
27.5
通讯作者：
Gutekunst, Kirstin
中科院分区：
文献类型：
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作者：
Makowka, Alexander;Nichelmann, Lars;Gutekunst, Kirstin
Entner-Doudoroff（艾德）途径是继Embden-Meyerhof-Parnas（EMP）途径和氧化戊糖磷酸（OPO）途径之后的第三条糖酵解途径。在这项研究中，出乎意料的是，我们观察到，删除艾德途径单独，甚至更明显的组合与其他糖酵解途径，减少光合自养生长在连续光的蓝藻集胞藻属PCC 6803。此外，我们发现，艾德途径所需的最佳糖原catalysts在平行的操作卡尔文-本森-Bassham（CBB）周期。与直觉相反的是，与CBB循环相反并且不提供任何额外的生物合成中间体的糖酵解途径在光合自养条件下是重要的。然而，对重新激活被抑制的CBB循环的能力的观察表明，它们形成糖酵解分流，利用细胞碳水化合物库来补充循环。总之，我们的研究结果表明，CBB循环作为一个自催化，完全自主的循环，完全依赖于自己的酶和CO2固定再生核酮糖-1，5-二磷酸Rubisco的经典观点是一个过于简单化。我们提出，与其他已知的自催化循环一样，CBB循环同样依赖于回补反应来补偿中间体的消耗，特别是在过渡态和自然界中常见的波动光照条件下。
The recent discovery of the Entner-Doudoroff (ED) pathway as a third glycolytic route beside Embden-Meyerhof-Parnas (EMP) and oxidative pentose phosphate (OPP) pathway in oxygenic photoautotrophs requires a revision of their central carbohydrate metabolism. In this study, unexpectedly, we observed that deletion of the ED pathway alone, and even more pronounced in combination with other glycolytic routes, diminished photoautotrophic growth in continuous light in the cyanobacterium Synechocystis sp. PCC 6803. Furthermore, we found that the ED pathway is required for optimal glycogen catabolism in parallel to an operating Calvin-Benson-Bassham (CBB) cycle. It is counter-intuitive that glycolytic routes, which are a reverse to the CBB cycle and do not provide any additional biosynthetic intermediates, are important under photoautotrophic conditions. However, observations on the ability to reactivate an arrested CBB cycle revealed that they form glycolytic shunts that tap the cellular carbohydrate reservoir to replenish the cycle. Taken together, our results suggest that the classical view of the CBB cycle as an autocatalytic, completely autonomous cycle that exclusively relies on its own enzymes and CO2 fixation to regenerate ribulose-1,5-bisphosphate for Rubisco is an oversimplification. We propose that in common with other known autocatalytic cycles, the CBB cycle likewise relies on anaplerotic reactions to compensate for the depletion of intermediates, particularly in transition states and under fluctuating light conditions that are common in nature.