Molecular Plant Physiology, Plant Science Division, Research School of Biology, College of Medicine, Biology and Environment, The Australian National University, Canberra, ACT, Australia.
Photosynth Res. 2011 Sep;109(1-3):33-45. doi: 10.1007/s11120-011-9659-8. Epub 2011 May 20.
Carboxysomes, containing the cell's complement of RuBisCO surrounded by a specialized protein shell, are a central component of the cyanobacterial CO(2)-concentrating mechanism. The ratio of two forms of the β-carboxysomal protein CcmM (M58 and M35) may affect the carboxysomal carbonic anhydrase (CcaA) content. We have over-expressed both M35 and M58 in the β-cyanobacterium Synechococcus PCC7942. Over-expression of M58 resulted in a marked increase in the amount of this protein in carboxysomes at the expense of M35, with a concomitant increase in the observed CcaA content of carboxysomes. Conversely, M35 over-expression diminished M58 content of carboxysomes and led to a decrease in CcaA content. Carboxysomes of air-grown wild-type cells contained slightly elevated CcaA and M58 content and slightly lower M35 content compared to their 2% CO(2)-grown counterparts. Over a range of CcmM expression levels, there was a strong correlation between M58 and CcaA content, indicating a constant carboxysomal M58:CcaA stoichiometry. These results also confirm a role for M58 in the recruitment of CcaA into the carboxysome and suggest a tight regulation of M35 and M58 translation is required to produce carboxysomes with an appropriate CA content. Analysis of carboxysomal protein ratios, resulting from the afore-mentioned over-expression studies, revealed that β-carboxysomal protein stoichiometries are relatively flexible. Determination of absolute protein quantities supports the hypothesis that M35 is distributed throughout the β-carboxysome. A modified β-carboxysome packing model is presented.
羧基体，包含 RuBisCO 酶及其周围的特殊蛋白壳，是蓝细菌 CO2 浓缩机制的核心组成部分。两种β-羧基体蛋白 CcmM（M58 和 M35）的比例可能会影响羧基体碳酸酐酶（CcaA）的含量。我们在β-蓝藻聚球藻 PCC7942 中过表达了 M35 和 M58。过表达 M58 导致羧基体中这种蛋白的含量显著增加，而 M35 减少，同时羧基体中观察到的 CcaA 含量也增加。相反，M35 的过表达减少了羧基体中的 M58 含量，并导致 CcaA 含量降低。与 2% CO2 生长的对应物相比，空气生长的野生型细胞的羧基体中 CcaA 和 M58 的含量略高，而 M35 的含量略低。在 CcmM 表达水平的范围内，M58 和 CcaA 含量之间存在很强的相关性，表明羧基体中 M58 和 CcaA 的比例是恒定的。这些结果还证实了 M58 在将 CcaA 招募到羧基体中的作用，并表明需要严格调节 M35 和 M58 的翻译，以产生具有适当 CA 含量的羧基体。对上述过表达研究中羧基体蛋白比例的分析表明，β-羧基体蛋白的比例相对灵活。绝对蛋白质数量的测定支持了 M35 分布在整个β-羧基体中的假设。提出了一种改良的β-羧基体包装模型。
