Visualizing Individual RuBisCO and Its Assembly into Carboxysomes in Marine Cyanobacteria by Cryo-Electron Tomography
Visualizing Individual RuBisCO and Its Assembly into Carboxysomes in Marine Cyanobacteria by Cryo-Electron Tomography
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DOI：
10.1016/j.jmb.2018.08.013
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发表时间：
2018-10-19
影响因子：
5.6
通讯作者：
Chiu, Wah
中科院分区：
文献类型：
--
作者：
Dai, Wei;Chen, Muyuan;Chiu, Wah
蓝细菌是光合生物，负责地球上25%的有机碳固定。碳固定的一个关键步骤是由核酮糖二磷酸羧化酶/加氧酶（RuBisCO）催化的，这是生物圈中最丰富的酶。应用Zernike相衬电子低温断层扫描和自动注释，我们确定了单个RuBisCO分子及其组装中间体，导致Syn5噬藻体感染的蓝细菌Synechococcus sp.WH8109细胞内形成羧基体。令人惊讶的是，更多的RuBisCO分子被发现存在作为细胞溶质的独立的复合物或簇比作为包装的组件内carboxysomes。胞质RuBisCO集群和部分组装的carboxysomes中确定的细胞断层扫描支持一个并行的组装模型，涉及蛋白质壳和封闭的RuBisCO。在成熟的羧基体中，RuBisCO既不是随机的，也不是严格的二十面体包装在可变大小的蛋白质壳内。时间平均的分子动力学模拟表明，半液体的概率分布的RuBisCO在carboxysomes和相关性以及与carboxysome subtomogram平均值。我们的结构观察揭示了RuBisCO组装的各个阶段，这对于理解细胞功能可能很重要。(C)2018爱思唯尔有限公司版权所有
Cyanobacteria are photosynthetic organisms responsible for similar to 25% of the organic carbon fixation on earth. A key step in carbon fixation is catalyzed by ribulose bisphosphate carboxylase/oxygenase (RuBisCO), the most abundant enzyme in the biosphere. Applying Zernike phase-contrast electron cryo-tomography and automated annotation, we identified individual RuBisCO molecules and their assembly intermediates leading to the formation of carboxysomes inside Syn5 cyanophage infected cyanobacteria Synechococcus sp. WH8109 cells. Surprisingly, more RuBisCO molecules were found to be present as cytosolic free-standing complexes or clusters than as packaged assemblies inside carboxysomes. Cytosolic RuBisCO clusters and partially assembled carboxysomes identified in the cell tomograms support a concurrent assembly model involving both the protein shell and the enclosed RuBisCO. In mature carboxysomes, RuBisCO is neither randomly nor strictly icosahedrally packed within protein shells of variable sizes. A time-averaged molecular dynamics simulation showed a semi-liquid probability distribution of the RuBisCO in carboxysomes and correlated well with carboxysome subtomogram averages. Our structural observations reveal the various stages of RuBisCO assemblies, which could be important for understanding cellular function. (C) 2018 Elsevier Ltd. All rights reserved.