Krajewski Stefanie S, Joswig Matthias, Nagel Miriam, Narberhaus Franz
Microbial Biology, Ruhr University Bochum, Bochum, Germany.
Environ Microbiol. 2014 Jun;16(6):1835-53. doi: 10.1111/1462-2920.12432. Epub 2014 Mar 27.
Small heat shock proteins (sHsps) including the well-studied IbpA protein from Escherichia coli are molecular chaperones that bind to non-native proteins and prevent them from aggregation. We discovered an entirely unexplored tricistronic small heat shock gene cluster in Pseudomonas putida. The genes pp3314, pp3313 and pp3312 (renamed to hspX, hspY and hspZ respectively) are transcribed in a single transcript. In addition to σ(32) -dependent transcriptional control, translation of the first and second gene of the operon is controlled by RNA thermometers with novel architectures. Biochemical analysis of HspY, HspZ and P. putida IbpA demonstrated that they assemble into homo-oligomers of different sizes whose quaternary structures alter in a temperature-dependent manner. IbpA and HspY are able to prevent the model substrate citrate synthase from thermal aggregation in vitro. Increased stress sensitivity of a P. putida strain lacking HspX, HspY and HspZ revealed an important role of these sHsps in stress adaptation. The hspXYZ operon is conserved among metabolically related bacteria that live in hostile environments including polluted soils. This heat shock operon might act as a protective system to promote survival in such ecological niches.
小热休克蛋白（sHsps），包括来自大肠杆菌的经过充分研究的IbpA蛋白，是分子伴侣，它们与非天然蛋白质结合并防止其聚集。我们在恶臭假单胞菌中发现了一个完全未被探索的三顺反子小热休克基因簇。基因pp3314、pp3313和pp3312（分别重新命名为hspX、hspY和hspZ）在单个转录本中被转录。除了依赖σ(32)的转录调控外，操纵子的第一个和第二个基因的翻译由具有新颖结构的RNA温度计控制。对HspY、HspZ和恶臭假单胞菌IbpA的生化分析表明，它们组装成不同大小的同型寡聚体，其四级结构随温度而改变。IbpA和HspY能够在体外防止模型底物柠檬酸合酶发生热聚集。缺乏HspX、HspY和HspZ的恶臭假单胞菌菌株对应激敏感性的增加揭示了这些sHsps在应激适应中的重要作用。hspXYZ操纵子在生活在包括污染土壤在内的恶劣环境中的代谢相关细菌中是保守的。这个热休克操纵子可能作为一种保护系统，以促进在这种生态位中的生存。
