A repeat protein links Rubisco to form the eukaryotic carbon-concentrating organelle
A repeat protein links Rubisco to form the eukaryotic carbon-concentrating organelle
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DOI：
10.1073/pnas.1522866113
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发表时间：
2016-05-24
影响因子：
11.1
通讯作者：
Jonikas, Martin C.
中科院分区：
文献类型：
--
作者：
Mackinder, Luke C. M.;Meyer, Moritz T.;Jonikas, Martin C.
生物碳固定是全球碳循环中的一个关键步骤，它在调节大气成分的同时，生产我们食用的食物和我们燃烧的燃料。全球大约三分之一的碳固定发生在一种被忽视的藻类细胞器——淀粉核中。淀粉核含有固定二氧化碳的酶Rubisco，并通过为Rubisco提供高浓度的二氧化碳来增强碳固定。自130多年前发现淀粉核以来，这种具有重要生态意义的细胞器的分子结构和生物发生一直是个谜。在这里，我们利用模式绿藻莱茵衣藻发现一种低复杂性重复蛋白——必需淀粉核成分1（EPYC1）将Rubisco连接起来形成淀粉核。我们发现EPYC1的含量与Rubisco相当，并在整个淀粉核中与Rubisco共定位。我们表明，在低二氧化碳条件下，EPYC1对于正常的淀粉核大小、数量、形态、Rubisco含量以及高效的碳固定是必不可少的。我们通过发现EPYC1结合Rubisco形成淀粉核基质来解释EPYC1在淀粉核生物发生中的核心作用。我们提出了两种模型，其中EPYC1的四个重复结构可能产生在莱茵衣藻淀粉核中观察到的Rubisco晶格排列。我们的研究结果表明了一个令人惊讶的简单分子机制，即Rubisco如何被包装形成淀粉核基质，这可能解释了Rubisco包装成淀粉核是如何通过趋同进化在广泛的光合真核生物中进化的。此外，我们的发现是朝着将淀粉核工程化引入作物以提高其碳固定效率迈出的关键一步。
Biological carbon fixation is a key step in the global carbon cycle that regulates the atmosphere's composition while producing the food we eat and the fuels we burn. Approximately one-third of global carbon fixation occurs in an overlooked algal organelle called the pyrenoid. The pyrenoid contains the CO2-fixing enzyme Rubisco and enhances carbon fixation by supplying Rubisco with a high concentration of CO2. Since the discovery of the pyrenoid more that 130 y ago, the molecular structure and biogenesis of this ecologically fundamental organelle have remained enigmatic. Here we use the model green alga Chlamydomonas reinhardtii to discover that a low-complexity repeat protein, Essential Pyrenoid Component 1 (EPYC1), links Rubisco to form the pyrenoid. We find that EPYC1 is of comparable abundance to Rubisco and colocalizes with Rubisco throughout the pyrenoid. We show that EPYC1 is essential for normal pyrenoid size, number, morphology, Rubisco content, and efficient carbon fixation at low CO2. We explain the central role of EPYC1 in pyrenoid biogenesis by the finding that EPYC1 binds Rubisco to form the pyrenoid matrix. We propose two models in which EPYC1's four repeats could produce the observed lattice arrangement of Rubisco in the Chlamydomonas pyrenoid. Our results suggest a surprisingly simple molecular mechanism for how Rubisco can be packaged to form the pyrenoid matrix, potentially explaining how Rubisco packaging into a pyrenoid could have evolved across a broad range of photosynthetic eukaryotes through convergent evolution. In addition, our findings represent a key step toward engineering a pyrenoid into crops to enhance their carbon fixation efficiency.