Bachhar Anushree, Jablonsky Jiri
Institute of Complex Systems, FFPW, University of South Bohemia, CENAKVA, Zamek 136, 373 33, Nove Hrady, Czech Republic.
Sci Rep. 2020 Dec 16;10(1):22018. doi: 10.1038/s41598-020-78475-z.
Phosphoketolase (PKET) pathway is predominant in cyanobacteria (around 98%) but current opinion is that it is virtually inactive under autotrophic ambient CO condition (AC-auto). This creates an evolutionary paradox due to the existence of PKET pathway in obligatory photoautotrophs. We aim to answer the paradox with the aid of bioinformatic analysis along with metabolic, transcriptomic, fluxomic and mutant data integrated into a multi-level kinetic model. We discussed the problems linked to neglected isozyme, pket2 (sll0529) and inconsistencies towards the explanation of residual flux via PKET pathway in the case of silenced pket1 (slr0453) in Synechocystis sp. PCC 6803. Our in silico analysis showed: (1) 17% flux reduction via RuBisCO for Δpket1 under AC-auto, (2) 11.2-14.3% growth decrease for Δpket2 in turbulent AC-auto, and (3) flux via PKET pathway reaching up to 252% of the flux via phosphoglycerate mutase under AC-auto. All results imply that PKET pathway plays a crucial role under AC-auto by mitigating the decarboxylation occurring in OPP pathway and conversion of pyruvate to acetyl CoA linked to EMP glycolysis under the carbon scarce environment. Finally, our model predicted that PKETs have low affinity to S7P as a substrate.
磷酸酮醇酶（PKET）途径在蓝细菌中占主导地位（约98%），但目前的观点认为，在自养环境CO条件（AC-自养）下，该途径实际上是无活性的。由于在 obligatory photoautotrophs中存在PKET途径，这就产生了一个进化悖论。我们旨在借助生物信息学分析以及整合到多层次动力学模型中的代谢、转录组、通量组和突变体数据来回答这个悖论。我们讨论了与被忽视的同工酶pket2（sll0529）相关的问题，以及在集胞藻PCC 6803中沉默pket1（slr0453）时，对通过PKET途径的残余通量解释的不一致性。我们的计算机模拟分析表明：（1）在AC-自养条件下，Δpket1通过RuBisCO的通量降低了17%；（2）在湍流AC-自养条件下，Δpket2的生长下降了11.2 - 14.3%；（3）在AC-自养条件下，通过PKET途径的通量达到了通过磷酸甘油酸变位酶通量的252%。所有结果都表明，在AC-自养条件下，PKET途径通过减轻在OPP途径中发生的脱羧作用以及在碳稀缺环境下将丙酮酸转化为与EMP糖酵解相关的乙酰辅酶A，发挥着关键作用。最后，我们的模型预测，PKETs对作为底物的S7P具有低亲和力。
