Minagawa Jun, Dann Marcel
Division of Environmental Photobiology, National Institute for Basic Biology (NIBB), Aichi, Okazaki 444-8585, Japan.
Plant Molecular Biology, Ludwig-Maximilian University (LMU) Munich, 82152 Planegg, Germany.
Plants (Basel). 2023 Jan 6;12(2):265. doi: 10.3390/plants12020265.
Cyanobacteria mostly rely on the active uptake of hydrated CO (i.e., bicarbonate ions) from the surrounding media to fuel their inorganic carbon assimilation. The dehydration of bicarbonate in close vicinity of RuBisCO is achieved through the activity of carboxysomal carbonic anhydrase (CA) enzymes. Simultaneously, many cyanobacterial genomes encode extracellular α- and β-class CAs (EcaA, EcaB) whose exact physiological role remains largely unknown. To date, the CahB1 enzyme of (formerly /) remains the sole described active extracellular β-CA in cyanobacteria, but its molecular features strongly suggest it to be a carboxysomal rather than a secreted protein. Upon expression of CahB1 in sp. PCC6803, we found that its expression complemented the loss of endogenous CcaA. Moreover, CahB1 was found to localize to a carboxysome-harboring and CA-active cell fraction. Our data suggest that CahB1 retains all crucial properties of a cellular carboxysomal CA and that the secretion mechanism and/or the machinations of the carboxysome are different from those of .
蓝藻大多依赖于从周围介质中主动摄取水合CO₂（即碳酸氢根离子）来为其无机碳同化提供燃料。在核酮糖-1,5-二磷酸羧化酶/加氧酶（RuBisCO）附近，碳酸氢根的脱水是通过羧基体碳酸酐酶（CA）的活性来实现的。同时，许多蓝藻基因组编码细胞外α-和β-类CA（EcaA、EcaB），但其确切的生理作用在很大程度上仍不清楚。迄今为止，（以前的/）的CahB1酶仍然是蓝藻中唯一被描述的有活性的细胞外β-CA，但它的分子特征强烈表明它是一种羧基体蛋白而非分泌蛋白。在 种PCC6803中表达CahB1后，我们发现其表达弥补了内源性CcaA的缺失。此外，发现CahB1定位于含有羧基体且有CA活性的细胞组分中。我们的数据表明，CahB1保留了细胞羧基体CA的所有关键特性，并且 羧基体的分泌机制和/或机制与 的不同。
