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BMC Evol Biol.:文建凡研究组揭示了两个重要光合作用酶的起源及其进化机制

  1. FSBPase
  2. 光合作用
  3. 卡尔文循环
  4. 进化

来源:中科院昆明动物所 2012-11-18 16:50

光合作用是地球上最重要的生物化学反应。通过光合作用,光合生物吸收太阳光能,将CO2固定,转变成化学能,作为地球上几乎所有有机物和能量的源头。其中执行CO2固定任务是由卡尔文循环途径来完成的。果糖-1,6-二磷酸酶(FBPase)和景天庚酮糖-1,7-二磷酸酶(SBPase)是真核光合生物卡尔文循环途径的两个受光调节的关键酶。

光合作用是地球上最重要的生物化学反应。通过光合作用,光合生物吸收太阳光能,将CO2固定,转变成化学能,作为地球上几乎所有有机物和能量的源头。其中执行CO2固定任务是由卡尔文循环途径来完成的。果糖-1,6-二磷酸酶(FBPase)和景天庚酮糖-1,7-二磷酸酶(SBPase)是真核光合生物卡尔文循环途径的两个受光调节的关键酶。在光合原核生物中,这两个酶的功能却由一个具有双功能的F/SBPase酶来承担。前人一直简单的以为,真核生物FBPase和SBPase二者由一个共同祖先――线粒体内共生起源时带来的原核型双功能酶F/SBPase分化而来。但是,该观点存在很多难以自圆其说之处。

在文建凡研究员的指导下,中国科学院昆明动物研究所研究生江永海和汪德勇通过大量的基因组的调查分析,首先发现:不同来源的原核F/SBPase双功能酶具有不同的domain――来源于变形菌的F/SBPase具有典型的I型FBPase domain,而来源于蓝细菌的F/SBPase却具有II型FBPase_GlpX domain。于是,首次提出原核生物双功能酶F/SBPase可以分为进化关系很远的I型和II型两类。更重要的是,通过较前人大得多的取样进行的分子系统学分析和motif分析,他们发现真核生物FBPase和SBPase并非起源于原核生物的两类双功能F/SBPase酶的任何一类,而是各自具有一个独立的起源:其中SBPase起源于ε变形菌的I型FBPase,而FBPase来源于一类目前未知细菌的I型FBPase,且各自独立进化出一套完善的光调节系统。进一步的分析表明,其中从I型FBPase到SBPase的进化是通过一种“from specialist to generalist”的机制而完成的。本研究不仅揭示了真核生物两种重要光合作用酶的来源,而且表明通过该进化过程使得真核生物的光合作用较原核生物的光合作用受到了更为精细的光调节。

本工作已于近期发表在BMC Evolutionary Biology杂志上。

本研究得到国家973项目、国家自然科学基金、中科院知识创新项目等的资助。(生物谷Bioon.com)

The independent prokaryotic origins of eukaryotic fructose-1, 6-bisphosphatase and sedoheptulose-1, 7-bisphosphatase and the implications of their origins for the evolution of eukaryotic Calvin cycle

Yong-Hai Jiang, De-Yong Wang and Jian-Fan Wen

Background

In the Calvin cycle of eubacteria, the dephosphorylations of both fructose-1, 6-bisphosphate (FBP) and sedoheptulose-1, 7-bisphosphate (SBP) are catalyzed by the same bifunctional enzyme: fructose-1, 6-bisphosphatase/sedoheptulose-1, 7-bisphosphatase (F/SBPase), while in that of eukaryotic chloroplasts by two distinct enzymes: chloroplastic fructose-1, 6-bisphosphatase (FBPase) and sedoheptulose-1, 7-bisphosphatase (SBPase), respectively. It was proposed that these two eukaryotic enzymes arose from the divergence of a common ancestral eubacterial bifunctional F/SBPase of mitochondrial origin. However, no specific affinity between SBPase and eubacterial FBPase or F/SBPase can be observed in the previous phylogenetic analyses, and it is hard to explain why SBPase and/or F/SBPase are/is absent from most extant nonphotosynthetic eukaryotes according to this scenario.

Results Domain analysis indicated that eubacterial F/SBPase of two different resources contain distinct domains: proteobacterial F/SBPases contain typical FBPase domain, while cyanobacterial F/SBPases possess FBPase_glpX domain. Therefore, like prokaryotic FBPase, eubacterial F/SBPase can also be divided into two evolutionarily distant classes (Class I and II). Phylogenetic analysis based on a much larger taxonomic sampling than previous work revealed that all eukaryotic SBPase cluster together and form a close sister group to the clade of epsilon-proteobacterial Class I FBPase which are gluconeogenesis-specific enzymes, while all eukaryotic chloroplast FBPase group together with eukaryotic cytosolic FBPase and form another distinct clade which then groups with the Class I FBPase of diverse eubacteria. Motif analysis of these enzymes also supports these phylogenetic correlations.

Conclusions There are two evolutionarily distant classes of eubacterial bifunctional F/SBPase. Eukaryotic FBPase and SBPase do not diverge from either of them but have two independent origins: SBPase share a common ancestor with the gluconeogenesis-specific Class I FBPase of epsilon-proteobacteria (or probably originated from that of the ancestor of epsilon-proteobacteria), while FBPase arise from Class I FBPase of an unknown kind of eubacteria. During the evolution of SBPase from eubacterial Class I FBPase, the SBP-dephosphorylation activity was acquired through the transition "from specialist to generalist". The evolutionary substitution of the endosymbiotic-origin cyanobacterial bifunctional F/SBPase by the two light-regulated substrate-specific enzymes made the regulation of the Calvin cycle more delicate, which contributed to the evolution of eukaryotic photosynthesis and even the entire photosynthetic eukaryotes.

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