Division of Biology, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA.
J Mol Biol. 2010 Feb 12;396(1):105-17. doi: 10.1016/j.jmb.2009.11.019. Epub 2009 Nov 17.
Carboxysomes are polyhedral inclusion bodies that play a key role in autotrophic metabolism in many bacteria. Using electron cryotomography, we examined carboxysomes in their native states within intact cells of three chemolithoautotrophic bacteria. We found that carboxysomes generally cluster into distinct groups within the cytoplasm, often in the immediate vicinity of polyphosphate granules, and a regular lattice of density frequently connects granules to nearby carboxysomes. Small granular bodies were also seen within carboxysomes. These observations suggest a functional relationship between carboxysomes and polyphosphate granules. Carboxysomes exhibited greater size, shape, and compositional variability in cells than in purified preparations. Finally, we observed carboxysomes in various stages of assembly, as well as filamentous structures that we attribute to misassembled shell protein. Surprisingly, no more than one partial carboxysome was ever observed per cell. Based on these observations, we propose a model for carboxysome assembly in which the shell and the internal RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) lattice form simultaneously, likely guided by specific interactions between shell proteins and RuBisCOs.
羧基体是多面内含体，在许多细菌的自养代谢中起着关键作用。使用电子晶体断层扫描，我们在三种化能自养细菌的完整细胞内研究了天然状态下的羧基体。我们发现，羧基体通常在细胞质内聚集形成不同的群组，通常靠近多磷酸盐颗粒，并且密度的规则晶格经常将颗粒与附近的羧基体连接起来。在羧基体内部也观察到了小的颗粒体。这些观察结果表明羧基体和多磷酸盐颗粒之间存在功能关系。与纯化制剂相比，羧基体在细胞中的大小、形状和组成变异更大。最后，我们观察到了处于不同组装阶段的羧基体，以及我们归因于错误组装的壳蛋白的丝状结构。令人惊讶的是，每个细胞中从未观察到超过一个部分羧基体。基于这些观察结果，我们提出了一个羧基体组装的模型，其中壳和内部 RuBisCO（核酮糖-1,5-二磷酸羧化酶/加氧酶）晶格同时形成，可能由壳蛋白和 RuBisCO 之间的特定相互作用引导。
