The ancestors of diatoms evolved a unique mitochondrial dehydrogenase to oxidize photorespiratory glycolate
The ancestors of diatoms evolved a unique mitochondrial dehydrogenase to oxidize photorespiratory glycolate
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硅藻的祖先进化出了一种独特的线粒体脱氢酶来氧化光呼吸乙醇酸
DOI：
10.1007/s11120-017-0355-1
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发表时间：
--
影响因子：
3.7
通讯作者：
Veronica G. Maurino
中科院分区：
文献类型：
--
作者：
Jessica Schmitz;Nishtala V. Srikanth;Meike Hüdig;Gereon Poschmann;Martin J. Lercher ;Veronica G. Maurino
像其他产氧光合生物一样，硅藻产生乙醇酸，一种有毒的中间体，作为Rubisco的加氧酶活性的结果。硅藻可以通过排泄和作为光呼吸途径的一部分的氧化来去除乙醇酸。三角褐指藻（Phaeodactylum tricornutum）编码两种被认为参与乙醇酸代谢的蛋白质：PtGO1和PtGO2。我们发现，这些蛋白质的序列有很大的不同，在其他物种，乙醇酸氧化酶（GOX）和乙醇酸脱氢酶的乙醇酸氧化的实验特征的蛋白质。我们证明PtGO1和PtGO2是P.与GOX同源的三角形。我们的系统发育分析表明，硅藻的祖先收购PtGO1在拟议的第一次二级内共生与绿藻类，这可能是以前从变形菌获得这个基因。相比之下，PtGO2是orthophosphate到一个未知的蛋白inGaldieria sulphuraria，与其收购过程中的第二次内共生与红色荧光素，引起了目前的质体。在保守位置的氨基酸残基的分析表明，PtGO2，它定位于过氧化物酶体，可能使用的底物以外的乙醇酸，解释缺乏GOX活性，我们体外培养。相反，PtGO1，而只有非常遥远的关系，以前的特点GOX蛋白，进化乙醇酸氧化活性，如凝胶活性测定和质谱分析所示。PtGO1定位于线粒体，与以前的建议，硅藻的光呼吸在这些细胞器中进行。我们的结论是，硅藻的祖先进化出一种独特的替代氧化光呼吸乙醇酸：线粒体脱氢酶同源GOX能够使用电子受体以外的O2。
Like other oxygenic photosynthetic organisms, diatoms produce glycolate, a toxic intermediate, as a consequence of the oxygenase activity of Rubisco. Diatoms can remove glycolate through excretion and through oxidation as part of the photorespiratory pathway. The diatomPhaeodactylum tricornutumencodes two proteins suggested to be involved in glycolate metabolism: PtGO1 and PtGO2. We found that these proteins differ substantially from the sequences of experimentally characterized proteins responsible for glycolate oxidation in other species, glycolate oxidase (GOX) and glycolate dehydrogenase. We show that PtGO1 and PtGO2 are the only sequences ofP. tricornutumhomologous to GOX. Our phylogenetic analyses indicate that the ancestors of diatoms acquired PtGO1 during the proposed first secondary endosymbiosis with a chlorophyte alga, which may have previously obtained this gene from proteobacteria. In contrast, PtGO2 is orthologous to an uncharacterized protein inGaldieria sulphuraria, consistent with its acquisition during the secondary endosymbiosis with a red alga that gave rise to the current plastid. The analysis of amino acid residues at conserved positions suggests that PtGO2, which localizes to peroxisomes, may use substrates other than glycolate, explaining the lack of GOX activity we observein vitro. Instead, PtGO1, while only very distantly related to previously characterized GOX proteins, evolved glycolate-oxidizing activity, as demonstrated by in gel activity assays and mass spectrometry analysis. PtGO1 localizes to mitochondria, consistent with previous suggestions that photorespiration in diatoms proceeds in these organelles. We conclude that the ancestors of diatoms evolved a unique alternative to oxidize photorespiratory glycolate: a mitochondrial dehydrogenase homologous to GOX able to use electron acceptors other than O2.
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