Australian Research Council Centre of Excellence for Translational Photosynthesis, Research School of Biology, The Australian National University, Building 134, Linnaeus Way, Acton, ACT, 2601, Australia.
Australian Research Council Centre of Excellence in Synthetic Biology, Research School of Chemistry, The Australian National University, Building 46, Sullivan's Creek Road, Acton, ACT, 2601, Australia.
Photosynth Res. 2023 May;156(2):265-277. doi: 10.1007/s11120-023-01009-x. Epub 2023 Mar 9.
Carboxysomes are bacterial microcompartments, whose structural features enable the encapsulated Rubisco holoenzyme to operate in a high-CO environment. Consequently, Rubiscos housed within these compartments possess higher catalytic turnover rates relative to their plant counterparts. This particular enzymatic property has made the carboxysome, along with associated transporters, an attractive prospect to incorporate into plant chloroplasts to increase future crop yields. To date, two carboxysome types have been characterized, the α-type that has fewer shell components and the β-type that houses a faster Rubisco. While research is underway to construct a native carboxysome in planta, work investigating the internal arrangement of carboxysomes has identified conserved Rubisco amino acid residues between the two carboxysome types which could be engineered to produce a new, hybrid carboxysome. In theory, this hybrid carboxysome would benefit from the simpler α-carboxysome shell architecture while simultaneously exploiting the higher Rubisco turnover rates in β-carboxysomes. Here, we demonstrate in an Escherichia coli expression system, that the Thermosynechococcus elongatus Form IB Rubisco can be imperfectly incorporated into simplified Cyanobium α-carboxysome-like structures. While encapsulation of non-native cargo can be achieved, T. elongatus Form IB Rubisco does not interact with the Cyanobium carbonic anhydrase, a core requirement for proper carboxysome functionality. Together, these results suggest a way forward to hybrid carboxysome formation.
羧基体是细菌的微结构，其结构特征使包裹的 Rubisco 全酶能够在高 CO 环境中运行。因此，这些隔间内的 Rubisco 相对于其植物对应物具有更高的催化周转率。这种特殊的酶学特性使得羧基体及其相关转运蛋白成为一种有吸引力的前景，可以将其纳入植物叶绿体中，以提高未来的作物产量。迄今为止，已经鉴定出两种羧基体类型，即壳成分较少的α型和容纳更快 Rubisco 的β型。虽然正在进行构建天然羧基体的研究，但对羧基体内部排列的研究已经确定了两种羧基体类型之间保守的 Rubisco 氨基酸残基，这些残基可以被工程化以产生新的、杂交的羧基体。从理论上讲，这种杂交羧基体将受益于更简单的α-羧基体壳结构，同时利用β-羧基体中更高的 Rubisco 周转率。在这里，我们在大肠杆菌表达系统中证明，嗜热栖热菌 elongatus 形式 IB Rubisco 可以不完全掺入简化的 Cyanobium α-羧基体样结构中。虽然可以实现非天然货物的封装，但 T. elongatus Form IB Rubisco 不会与 Cyanobium 碳酸酐酶相互作用，而碳酸酐酶是羧基体正常功能的核心要求。总之，这些结果为杂交羧基体的形成提供了一种方法。
