Pathway and Importance of Photorespiratory 2-Phosphoglycolate Metabolism in Cyanobacteria
Pathway and Importance of Photorespiratory 2-Phosphoglycolate Metabolism in Cyanobacteria
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DOI：
10.1007/978-1-4419-1528-3_6
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发表时间：
2010-01-01
期刊：
影响因子：
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通讯作者：
Bauwe, Hermann
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文献类型：
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作者：
Hagemann, Martin;Eisenhut, Marion;Bauwe, Hermann
蓝藻在35亿年前发明了光合作用。副产物分子氧引发光合生物中主要羧化酶RubisCO的加氧反应。在加氧酶反应期间，产生有毒副产物2-磷酸乙醇酸（2-PG），并且必须快速代谢。光呼吸2-PG代谢被高等植物用于此目的。蓝藻中存在活性2-PG代谢一直是争议的主题，因为这些生物已经进化出一种有效的碳浓缩机制（CCM），这将大大降低RubisCO的加氧酶活性。基于新出现的蓝藻基因组信息，我们已经发现了明确的迹象，可能参与光呼吸2-PG代谢的许多基因的存在。使用的模式集胞藻属菌株PCC 6803的遗传方法，我们产生并表征这些基因中定义的突变体，以验证它们的功能。我们的研究结果表明，蓝细菌进行积极的光呼吸2-PG代谢，这在集胞藻中采用三种途径：植物样循环，细菌样甘油酸途径，和一个完整的脱羧分支。除了2-PG的解毒，这种必要的代谢有助于蓝藻细胞适应强光条件。
Cyanobacteria invented oxygenic photosynthesis about 3.5 billion years ago. The by-product molecular oxygen initiated the oxygenase reaction of RubisCO, the main carboxylating enzyme in photosynthetic organisms. During oxygenase reaction, the toxic side product 2-phosphoglycolate (2-PG) is produced and must be quickly metabolized. Photorespiratory 2-PG metabolism is used for this purpose by higher plants. The existence of an active 2-PG metabolism in cyanobacteria has been the subject of controversy since these organisms have evolved an efficient carbon-concentrating mechanism (CCM), which should considerably reduce the oxygenase activity of RubisCO. Based on emerging cyanobacterial genomic information, we have found clear indications for the existence of many genes possibly involved in the photorespiratory 2-PG metabolism. Using a genetic approach with the model Synechocystis sp. strain PCC 6803, we generated and characterized defined mutants in these genes to verify their function. Our results show that cyanobacteria perform an active photorespiratory 2-PG metabolism, which employs three routes in Synechocystis: a plant-like cycle, a bacterial-like glycerate pathway, and a complete decarboxylation branch. In addition to the detoxification of 2-PG, this essential metabolism helps cyanobacterial cells acclimate to high light conditions.