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

碳储备聚合物的合成和转化在蓝藻代谢的自养-异养转换过程中起着关键作用。通过与SCyCode合作伙伴Gutekunst，Hagemann和Macek的合作，我们对碳储存代谢及其调节的理解可以在我们最近的工作中取得重大进展。使用模式生物集胞藻PCC 6803，我们可以表明，两个碳储存聚合物，糖原和聚羟基丁酸酯（PHB）通过Emden-Meyerhof-Parnas途径的糖酵解通量相互连接。糖原和PHB之间的碳通量在磷酸甘油酸酯酶催化的3-磷酸甘油酸酯（3-PGA）向2-PGA的相互转化中受到关键控制，这是异养-自养转换的主要控制点。当集胞藻缺乏结合氮源时，糖原的储存变得至关重要。当结合氮源再次可用时，代谢迅速切换到消耗糖原的异养模式。在这种情况下，能量稳态最初是基于钠基序力依赖性ATP再生在细胞质膜。氮同化反应的激活然后启动糖原降解，其仅由两种糖原磷酸化酶同工酶（GlgP 2）中的一种催化。我们发现葡萄糖-1P（Glc-1 P）通过磷酸葡萄糖变位酶（PGM）向Glc-6P的后续转化受到似乎在哺乳动物PGM中保守的调节性PGM-丝氨酰-磷酸化的严格控制。此外，PGM与随后的分解代谢酶Glc-6P脱氢酶（G6 PDH）形成氧化还原依赖性瞬时复合物（代谢物），由氧化还原控制的连接蛋白（OpcA）介导。我们推测，这种复合物的形成指导糖酵解碳流向氧化戊糖磷酸途径。这种调节复合物应该防止流入糖酵解EMP途径，在氮饥饿细胞的重新绿化过程中阻止。在第二个资助期内，我们的目标是对PGM-OpcA-G6 PDH代谢子形成的结构-功能进行阐明，此外还旨在解决糖原代谢机制的明显新颖的调节特性及其在基于模型的方法辅助下整合到整个细胞过程中。

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.