Regulation of glycogen metabolism in response to the autotrophy-heterotrophy switch in Cyanobacteria

碳储备聚合物的合成和翻转在蓝藻代谢的自养-异养转换中起着关键作用。在与SCyCode合作伙伴Gutekunst、Hagemann和Macek的合作下，我们最近的工作可能在理解碳储存新陈代谢及其调控方面取得重大进展。利用模式生物聚球藻PCC6803，我们可以证明糖原和聚羟基丁酸酯(PHB)这两种储碳聚合物通过Emden-Meyerhof-Parns途径通过糖酵解通量相互连接。糖原和PHB之间的碳流是由磷酸甘油变位酶催化的3-磷酸甘油酸酯(3-PGA)到2-PGA相互转化的关键控制点，是异养-自养转换的主要控制点。当聚球藻对结合氮源缺乏时，糖原储存变得至关重要。当结合氮源再次可用时，新陈代谢迅速切换到消耗糖原的异养模式。在这种情况下，能量平衡最初建立在细胞膜上钠基序依赖的ATP再生的基础上。氮同化反应的激活然后启动糖原降解，这只由两个糖原磷酸化酶同工酶中的一个(GlgP2)催化。我们发现，随后通过磷酸葡萄糖变位酶(PGM)将葡萄糖-1P(GLC-1P)转化为GLC-6P的过程受到调控的PGM-丝氨酸-磷酸化的严格控制，这种磷酸化似乎在哺乳动物PGM中是保守的。此外，PGM由氧化还原控制的连接蛋白(OPCA)介导，与随后的分解代谢酶GLC-6P脱氢酶(G6PDH)形成氧化还原依赖的瞬时复合体(代谢产物)。我们假设这种复合体的形成将糖酵解碳流导向氧化戊糖磷酸途径。这种调节复合体应该防止进入糖酵解EMP途径的流量，这在氮饥饿细胞的重新绿化过程中是必不可少的。在第二个资助期，我们的目标是阐明PGM-OPCA-G6PDH代谢子形成的结构-功能，并进一步致力于解决糖原代谢机制的明显新的调节特性，以及它在基于模型的方法帮助下在整个细胞过程中的整合。

The synthesis and turn-over of carbon reserve polymers plays a pivotal role in the autotrophy-heterotrophy switch in cyanobacterial metabolism. In collaboration with SCyCode partners Gutekunst, Hagemann and Macek, major advances in our understanding of carbon-storage metabolism and its regulation could be achieved in our recent work. Using the model organism Synechocystis PCC 6803 we could show that the two carbon storage polymers, glycogen and polyhydroxybutyrate (PHB) are interconnected by glycolytic flux through the Emden-Meyerhof-Parnas pathway. Carbon flux between glycogen and PHB is critically controlled at the phosphoglycerate mutase catalyzed interconversion of 3-phosphoglycerate (3-PGA) to 2-PGA, which turns out as a major control point of the heterotrophy-autotrophy switch. Glycogen storage becomes essential, when Synechocystis is starved for combined nitrogen sources. Metabolism switches rapidly to glycogen-consuming, heterotrophic mode, when combined nitrogen sources become available again. In this situation, energy homeostasis is initially based on sodium-motif force-dependent ATP regeneration at the cytoplasmic membrane. The activation of nitrogen-assimilatory reactions then initiates glycogen degradation, which is catalyzed by only one of the two glycogen phosphorylase isoenzymes (GlgP2). We found that the subsequent conversion of Glucose-1P (Glc-1P) to Glc-6P through phosphoglucomutase (PGM) is tightly controlled by a regulatory PGM-seryl-phosphorylation that appears to be conserved in mammalian PGM. Moreover, PGM forms a redox-dependent transient complex (a metabolon) with the subsequent catabolic enzyme, the Glc-6P dehydrogenase (G6PDH), mediated by a redox-controlled connector protein (OpcA). We hypothesize that formation of this complex directs the glycolytic carbon flow towards the oxidative pentose phosphate pathway. This regulatory complex should prevent flux into the glycolytic EMP pathway, dispensable during the re-greening of nitrogen-starved cells. In the second funding period, we aim towards a structure-functional elucidation of PGM-OpcA-G6PDH metabolon formation and moreover aim towards resolving apparently novel regulatory properties of the glycogen metabolic machinery and its integration in the overall cellular processes aided by model-based approaches.