Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA.
Biological Sciences Department, Purdue University, West Lafayette, IN, USA.
Nat Commun. 2022 Aug 18;13(1):4863. doi: 10.1038/s41467-022-32584-7.
Despite the importance of microcompartments in prokaryotic biology and bioengineering, structural heterogeneity has prevented a complete understanding of their architecture, ultrastructure, and spatial organization. Here, we employ cryo-electron tomography to image α-carboxysomes, a pseudo-icosahedral microcompartment responsible for carbon fixation. We have solved a high-resolution subtomogram average of the Rubisco cargo inside the carboxysome, and determined the arrangement of the enzyme. We find that the H. neapolitanus Rubisco polymerizes in vivo, mediated by the small Rubisco subunit. These fibrils can further pack to form a lattice with six-fold pseudo-symmetry. This arrangement preserves freedom of motion and accessibility around the Rubisco active site and the binding sites for two other carboxysome proteins, CsoSCA (a carbonic anhydrase) and the disordered CsoS2, even at Rubisco concentrations exceeding 800 μM. This characterization of Rubisco cargo inside the α-carboxysome provides insight into the balance between order and disorder in microcompartment organization.
尽管微区室在原核生物学和生物工程中非常重要，但结构异质性阻碍了人们对其结构、超微结构和空间组织的全面理解。在这里，我们使用冷冻电子断层扫描来对 α-羧酶体进行成像，这是一种负责碳固定的拟二十面体微区室。我们已经解决了羧酶体内 Rubisco 货物的高分辨率亚断层平均图像，并确定了酶的排列方式。我们发现，来自 H. neapolitanus 的 Rubisco 在体内聚合，由小的 Rubisco 亚基介导。这些原纤维可以进一步包装，形成具有六重拟对称的晶格。这种排列方式在 Rubisco 浓度超过 800 μM 的情况下，保持了 Rubisco 活性位点及其它两个羧酶体蛋白（碳酸酐酶 CsoSCA 和无规卷曲的 CsoS2）周围运动和可及性的自由度。这种对 α-羧酶体内部 Rubisco 货物的描述提供了对微区室组织中有序和无序之间平衡的深入了解。
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