Majeran Wojciech, Wostrikoff Katia, Wollman Francis-André, Vallon Olivier
Institute of Plant Sciences Paris-Saclay (IPS2), CNRS, Université Paris-Diderot, Université Paris-Sud, INRA, Université Evry, Université Paris-Saclay, Rue de Noetzlin, 91190 Gif-sur-Yvette, France.
UMR7141 CNRS/Sorbonne Université, Institut de Biologie Physico-Chimique, 13 rue Pierre et Marie Curie, 75005 Paris, France.
Plants (Basel). 2019 Jun 26;8(7):191. doi: 10.3390/plants8070191.
Ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) associates a chloroplast- and a nucleus-encoded subunit (LSU and SSU). It constitutes the major entry point of inorganic carbon into the biosphere as it catalyzes photosynthetic CO fixation. Its abundance and richness in sulfur-containing amino acids make it a prime source of N and S during nutrient starvation, when photosynthesis is downregulated and a high RuBisCO level is no longer needed. Here we show that translational attenuation of ClpP1 in the green alga results in retarded degradation of RuBisCO during S- and N-starvation, suggesting that the Clp protease is a major effector of RubisCO degradation in these conditions. Furthermore, we show that ClpP cannot be attenuated in the context of point mutations that prevent LSU folding. The mutant LSU remains in interaction with the chloroplast chaperonin complex. We propose that degradation of the mutant LSU by the Clp protease is necessary to prevent poisoning of the chaperonin. In the total absence of LSU, attenuation of ClpP leads to a dramatic stabilization of unassembled SSU, indicating that Clp is responsible for its degradation. In contrast, attenuation of ClpP in the absence of SSU does not lead to overaccumulation of LSU, whose translation is controlled by assembly. Altogether, these results point to RuBisCO degradation as one of the major house-keeping functions of the essential Clp protease. In addition, we show that non-assembled subunits of the ATP synthase are also stabilized when ClpP is attenuated. In the case of the mutation, this can even allow the assembly of a small amount of CF1, which partially restores phototrophy.
1,5-二磷酸核酮糖羧化酶/加氧酶（RuBisCO）由一个叶绿体编码亚基和一个细胞核编码亚基（大亚基和小亚基）组成。它催化光合二氧化碳固定，是无机碳进入生物圈的主要入口。其丰富性以及含硫氨基酸的含量使其成为营养饥饿期间氮和硫的主要来源，此时光合作用下调，不再需要高含量的RuBisCO。在这里，我们表明绿藻中ClpP1的翻译衰减导致在硫和氮饥饿期间RuBisCO的降解延迟，这表明Clp蛋白酶是这些条件下RubisCO降解的主要效应因子。此外，我们表明在阻止大亚基折叠的点突变背景下，ClpP无法被衰减。突变的大亚基仍与叶绿体伴侣蛋白复合体相互作用。我们提出，Clp蛋白酶对突变大亚基的降解对于防止伴侣蛋白中毒是必要的。在完全没有大亚基的情况下，ClpP的衰减导致未组装的小亚基显著稳定，表明Clp负责其降解。相反，在没有小亚基的情况下ClpP的衰减不会导致大亚基的过度积累，大亚基的翻译受组装控制。总之，这些结果表明RuBisCO降解是必需的Clp蛋白酶的主要看家功能之一。此外，我们表明当ClpP衰减时，ATP合酶的未组装亚基也会稳定。在突变的情况下，这甚至可以允许少量CF1的组装，从而部分恢复光合营养。
