Küberl Andreas, Polen Tino, Bott Michael
IBG-1: Biotechnology, Institute of Bio- and Geosciences, Forschungszentrum Jülich, 52425 Juelich, Germany.
IBG-1: Biotechnology, Institute of Bio- and Geosciences, Forschungszentrum Jülich, 52425 Juelich, Germany
Proc Natl Acad Sci U S A. 2016 Apr 26;113(17):4806-11. doi: 10.1073/pnas.1514529113. Epub 2016 Apr 12.
The balance of sufficient iron supply and avoidance of iron toxicity by iron homeostasis is a prerequisite for cellular metabolism and growth. Here we provide evidence that, in Actinobacteria, pupylation plays a crucial role in this process. Pupylation is a posttranslational modification in which the prokaryotic ubiquitin-like protein Pup is covalently attached to a lysine residue in target proteins, thus resembling ubiquitination in eukaryotes. Pupylated proteins are recognized and unfolded by a dedicated AAA+ ATPase (Mycobacterium proteasomal AAA+ ATPase; ATPase forming ring-shaped complexes). In Mycobacteria, degradation of pupylated proteins by the proteasome serves as a protection mechanism against several stress conditions. Other bacterial genera capable of pupylation such as Corynebacterium lack a proteasome, and the fate of pupylated proteins is unknown. We discovered that Corynebacterium glutamicum mutants lacking components of the pupylation machinery show a strong growth defect under iron limitation, which was caused by the absence of pupylation and unfolding of the iron storage protein ferritin. Genetic and biochemical data support a model in which the pupylation machinery is responsible for iron release from ferritin independent of degradation.
通过铁稳态实现充足的铁供应与避免铁毒性之间的平衡是细胞代谢和生长的先决条件。在此，我们提供证据表明，在放线菌中，小泛素样修饰蛋白（Pup）化在这一过程中起着关键作用。Pup化是一种翻译后修饰，其中原核泛素样蛋白Pup共价连接到靶蛋白中的赖氨酸残基上，因此类似于真核生物中的泛素化。Pup化蛋白被一种专门的AAA+ATP酶（分枝杆菌蛋白酶体AAA+ATP酶；形成环形复合物的ATP酶）识别并展开。在分枝杆菌中，蛋白酶体对Pup化蛋白的降解作为一种针对多种应激条件的保护机制。其他能够进行Pup化的细菌属，如棒状杆菌，缺乏蛋白酶体，Pup化蛋白的命运尚不清楚。我们发现，缺乏Pup化机制成分的谷氨酸棒状杆菌突变体在铁限制条件下表现出强烈的生长缺陷，这是由于铁储存蛋白铁蛋白缺乏Pup化和展开所致。遗传和生化数据支持一种模型，即Pup化机制负责从铁蛋白中释放铁，而与降解无关。
