心磷脂（cardiolipin）同時是真核細胞線粒體內(nèi)膜和原核細胞細菌膜上的重要結(jié)構(gòu)和功能成分,。該事實被認為是支持線粒體是由細菌內(nèi)共生起源而來的重要證據(jù)之一。然而,，一般認為心磷脂的生物合成在細菌和真核生物中分別是由具有不同結(jié)構(gòu)域的兩種不同類型的心磷脂合成酶（CLS）,，即CLS_pld和CLS_cap來催化完成的。這就產(chǎn)生了一個重要問題：為什么真核細胞線粒體心磷脂的合成途徑不是由細菌內(nèi)共生直接帶入?yún)s出現(xiàn)不同,？從原核生物進化成真核生物的過程中,，真核生物的心磷脂合成途徑究竟有著怎樣的起源？隨著真核生物的分化,，該途徑又經(jīng)歷了怎樣的進化,？
中國科學院昆明動物研究所真核細胞進化基因組學研究組田海峰博士在導師文建凡研究員的指導下，首先對心磷脂合成及其成熟酶在整個生物三大部類（Domain）中的分布進行了系統(tǒng)地調(diào)查,。結(jié)果發(fā)現(xiàn)：1）盡管大部分真細菌中存在的是CLS_pld途徑,，但是在包括變形菌和放線菌等一部分真細菌中已經(jīng)出現(xiàn)了過去被認為是真核型的CLS_cap途徑；2）盡管所有多細胞生物和部分單細胞真核生物普遍具有CLS_cap途徑,，但在很多單細胞的原生生物中卻只具有過去被認為是原核型的CLS_pld途徑,；3）心磷脂成熟酶為真核生物所特有，而不存在于原核生物中,。其次,，分子系統(tǒng)分析結(jié)果顯示，真核生物所具有的CLS_cap途徑與α蛋白菌的CLS_cap途徑的親緣關系最為接近,；部分單細胞原生生物中發(fā)現(xiàn)的CLS_pld途徑雖然也與細菌中的CLS_pld途徑關系密切但不能確定來源于哪一類特定的細菌,；心磷脂成熟酶均是在真核生物起源后通過別的基因的duplication等途徑而進化出來的。
據(jù)以上研究事實，研究人員勾勒出了心磷脂合成和成熟途徑在整個生物界中的演化歷史脈絡圖：真核生物的最早共同祖先（FECA）從原核祖先中獲得了CLS_pld途徑,；之后,，在真核生物最近共同祖先（LECA）中，內(nèi)共生的線粒體又帶來了CLS_cap途徑,；此時,，不同的原生生物出現(xiàn)了不同的選擇，其中選擇了CLS_cap的成為了有機會進化成多細胞真核生物的原生生物類群,。心磷脂成熟途徑出現(xiàn)在真核生物產(chǎn)生之后,，而且，該途徑在不同生物中的多樣性可能是適應性進化的結(jié)果,；而“無線粒體”原生生物（如藍氏賈第蟲）中缺少心磷脂合成與成熟途徑，很可能是因為二次丟失造成的,。
這些研究結(jié)果對加深人們認識真核生物代謝途徑的進化具有重要意義,。（生物谷 bioon.com）
doi:10.1186/1471-2148-12-32
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The evolution of cardiolipin biosynthesis and maturation pathways and its implications for the evolution of eukaryotes
Hai-Feng Tian, Jin-Mei Feng，Jian-Fan Wen
Background Cardiolipin (CL) is an important component in mitochondrial inner and bacterial membranes. Its appearance in these two biomembranes has been considered as evidence of the endosymbiotic origin of mitochondria. But CL was reported to be synthesized through two distinct enzymes--CLS_cap and CLS_pld in eukaryotes and bacteria. Therefore, how the CL biosynthesis pathway evolved is an interesting question. Results Phylogenetic distribution investigation of CL synthase (CLS) showed: most bacteria have CLS_pld pathway, but in partial bacteria including proteobacteria and actinobacteria CLS_cap pathway has already appeared; in eukaryotes, Supergroup Opisthokonta and Archaeplastida, and Subgroup Stramenopiles, which all contain multicellular organisms, possess CLS_cap pathway, while Supergroup Amoebozoa and Excavata and Subgroup Alveolata, which all consist exclusively of unicellular eukaryotes, bear CLS_pld pathway; amitochondriate protists in any supergroups have neither. Phylogenetic analysis indicated the CLS_cap in eukaryotes have the closest relationship with those of alpha proteobacteria, while the CLS_pld in eukaryotes share a common ancestor but have no close correlation with those of any particular bacteria. Conclusions The first eukaryote common ancestor (FECA) inherited the CLS_pld from its bacterial ancestor (e. g. the bacterial partner according to any of the hypotheses about eukaryote evolution); later, when the FECA evolved into the last eukaryote common ancestor (LECA), the endosymbiotic mitochondria (alpha proteobacteria) brought in CLS_cap, and then in some LECA individuals the CLS_cap substituted the CLS_pld, and these LECAs would evolve into the protist lineages from which multicellular eukaryotes could arise, while in the other LECAs the CLS_pld was retained and the CLS_cap was lost, and these LECAs would evolve into the protist lineages possessing CLS_pld. Besides, our work indicated CL maturation pathway arose after the emergence of eukaryotes probably through mechanisms such as duplication of other genes, and gene duplication and loss occurred frequently at different lineage levels, increasing the pathway diversity probably to fit the complicated cellular process in various cells. Our work also implies the classification putting Stramenopiles and Alveolata together to form Chromalveolata may be unreasonable; the absence of CL synthesis and maturation pathways in amitochondriate protists is most probably due to secondary loss.
