Institute of Biochemistry and Biotechnology, Martin-Luther-University Halle-Wittenberg, Kurt-Mothes-Str. 3a, 06120, Halle, Saale, Germany.
Biocenter of the University, Martin-Luther-University Halle-Wittenberg, Weinbergweg 22, 06120, Halle, Saale, Germany.
Nat Commun. 2020 Apr 3;11(1):1662. doi: 10.1038/s41467-020-15539-8.
The proteasome is an essential protein-degradation machinery in eukaryotic cells that controls protein turnover and thereby the biogenesis and function of cell organelles. Chloroplasts import thousands of nuclear-encoded precursor proteins from the cytosol, suggesting that the bulk of plastid proteins is transiently exposed to the cytosolic proteasome complex. Therefore, there is a cytosolic equilibrium between chloroplast precursor protein import and proteasomal degradation. We show here that a shift in this equilibrium, induced by mild genetic proteasome impairment, results in elevated precursor protein abundance in the cytosol and significantly increased accumulation of functional photosynthetic complexes in protein import-deficient chloroplasts. Importantly, a proteasome lid mutant shows improved photosynthetic performance, even in the absence of an import defect, signifying that functional precursors are continuously degraded. Hence, turnover of plastid precursors in the cytosol represents a mechanism to constrain thylakoid membrane assembly and photosynthetic electron transport.
蛋白酶体是真核细胞中一种重要的蛋白质降解机制，它控制着蛋白质的周转，从而影响细胞器官的生物发生和功能。叶绿体从细胞质中导入数千种核编码的前体蛋白，这表明大部分质体蛋白是暂时暴露在细胞质蛋白酶体复合物中的。因此，在叶绿体前体蛋白的导入和蛋白酶体降解之间存在细胞质平衡。我们在这里表明，这种平衡的转变，由轻度遗传蛋白酶体损伤引起，导致细胞质中前体蛋白丰度升高，并显著增加了在蛋白质导入缺陷的叶绿体中功能性光合作用复合物的积累。重要的是，蛋白酶体盖突变体表现出改善的光合作用性能，即使在没有导入缺陷的情况下也是如此，这表明功能性前体蛋白是不断降解的。因此，质体前体在细胞质中的周转代表了一种限制类囊体膜组装和光合作用电子传递的机制。
