Unconventional biochemical regulation of the oxidative pentose phosphate pathway in the model cyanobacterium Synechocystis sp. PCC 6803
Unconventional biochemical regulation of the oxidative pentose phosphate pathway in the model cyanobacterium Synechocystis sp. PCC 6803
复制标题
DOI：
10.1042/bcj20200038
复制
发表时间：
2020-04-01
影响因子：
4.1
通讯作者：
Osanai, Takashi
中科院分区：
文献类型：
--
作者：
Ito, Shoki;Osanai, Takashi
利用蓝藻中的糖催化剂从二氧化碳中生产代谢产物最近一直是人们关注的焦点。集胞藻属PCC 6803（Synechocystis 6803）是研究最多的代谢产物产生的蓝细菌。先前的体内分析表明，氧化戊糖磷酸（pentose phosphate，pentose phosphate）途径是集胞藻6803糖代谢的核心。然而，在集胞藻6803中的β-内酰胺酶途径酶的生化调节仍然未知。因此，我们的特点是一个关键的酶，葡萄糖-6-磷酸脱氢酶（G6 PDH），和相关酶集胞藻6803。集胞藻6803 G6 PDH在氧化三羧酸（TCA）循环中被柠檬酸盐抑制。柠檬酸盐以前未被报道为G6 PDH的抑制剂。同样，6-磷酸葡萄糖酸脱氢酶，另一种来自集胞藻6803的酶，催化NADPH途径中的NADPH生成反应，被柠檬酸盐抑制。为了理解这种抑制的生理意义，我们表征了来自集胞藻6803（SySSADH）的琥珀酸半醛脱氢酶（SSADH），其催化氧化TCA循环中的NAD（P）H生成反应之一。与来自集胞藻6803的异柠檬酸脱氢酶类似，SySSADH特异性地催化NADPH生成反应，并且不被柠檬酸盐抑制。SySSADH的活性低于其他细菌SSADH。先前和本研究表明，与NADPH途径不同，氧化TCA循环是集胞藻6803中NADPH生成效率低的途径。因此，有人建议，为了避免NADPH的过度生产，当集胞藻6803中氧化TCA循环的流量增加时，抑制NADPH途径脱氢酶活性。
Metabolite production from carbon dioxide using sugar catabolism in cyanobacteria has been in the spotlight recently. Synechocystis sp. PCC 6803 (Synechocystis 6803) is the most studied cyanobacterium for metabolite production. Previous in vivo analyses revealed that the oxidative pentose phosphate (OPP) pathway is at the core of sugar catabolism in Synechocystis 6803. However, the biochemical regulation of the OPP pathway enzymes in Synechocystis 6803 remains unknown. Therefore, we characterized a key enzyme of the OPP pathway, glucose-6-phosphate dehydrogenase (G6PDH), and related enzymes from Synechocystis 6803. Synechocystis 6803 G6PDH was inhibited by citrate in the oxidative tricarboxylic acid (TCA) cycle. Citrate has not been reported as an inhibitor of G6PDH before. Similarly, 6-phosphogluconate dehydrogenase, the other enzyme from Synechocystis 6803 that catalyzes the NADPH-generating reaction in the OPP pathway, was inhibited by citrate. To understand the physiological significance of this inhibition, we characterized succinic semialdehyde dehydrogenase (SSADH) from Synechocystis 6803 (SySSADH), which catalyzes one of the NAD(P)H generating reactions in the oxidative TCA cycle. Similar to isocitrate dehydrogenase from Synechocystis 6803, SySSADH specifically catalyzed the NADPH-generating reaction and was not inhibited by citrate. The activity of SySSADH was lower than that of other bacterial SSADHs. Previous and this studies revealed that unlike the OPP pathway, the oxidative TCA cycle is a pathway with low efficiency in NADPH generation in Synechocystis 6803. It has, thus, been suggested that to avoid NADPH overproduction, the OPP pathway dehydrogenase activity is repressed when the flow of the oxidative TCA cycle increases in Synechocystis 6803.