Department of Chemistry, Center for Integrated Protein Science, Technische Universität München, D-85748 Garching, Germany.
Proc Natl Acad Sci U S A. 2012 Dec 11;109(50):20407-12. doi: 10.1073/pnas.1209565109. Epub 2012 Nov 26.
Small heat shock proteins (sHsps) are molecular chaperones that prevent the aggregation of nonnative proteins. The sHsps investigated to date mostly form large, oligomeric complexes. The typical bacterial scenario seemed to be a two-component sHsps system of two homologous sHsps, such as the Escherichia coli sHsps IbpA and IbpB. With a view to expand our knowledge on bacterial sHsps, we analyzed the sHsp system of the bacterium Deinococcus radiodurans, which is resistant against various stress conditions. D. radiodurans encodes two sHsps, termed Hsp17.7 and Hsp20.2. Surprisingly, Hsp17.7 forms only chaperone active dimers, although its crystal structure reveals the typical α-crystallin fold. In contrast, Hsp20.2 is predominantly a 36mer that dissociates into smaller oligomeric assemblies that bind substrate proteins stably. Whereas Hsp20.2 cooperates with the ATP-dependent bacterial chaperones in their refolding, Hsp17.7 keeps substrates in a refolding-competent state by transient interactions. In summary, we show that these two sHsps are strikingly different in their quaternary structures and chaperone properties, defining a second type of bacterial two-component sHsp system.
小分子热休克蛋白（sHsps）是一种分子伴侣，可以防止非天然蛋白质聚集。迄今为止研究过的 sHsp 大多形成大型寡聚复合物。典型的细菌情况似乎是由两个同源 sHsps 组成的二组分 sHsps 系统，例如大肠杆菌 sHsps IbpA 和 IbpB。为了扩展我们对细菌 sHsps 的了解，我们分析了耐各种应激条件的细菌 Deinococcus radiodurans 的 sHsp 系统。D. radiodurans 编码两种 sHsps，称为 Hsp17.7 和 Hsp20.2。令人惊讶的是，尽管其晶体结构揭示了典型的 α-晶状体折叠，但 Hsp17.7 仅形成具有伴侣活性的二聚体。相比之下，Hsp20.2 主要是 36mer，可解离成较小的寡聚体组装，稳定结合底物蛋白。虽然 Hsp20.2 与 ATP 依赖性细菌伴侣蛋白在重折叠过程中合作，但 Hsp17.7 通过瞬时相互作用使底物保持在重折叠状态。总之，我们表明这两种 sHsps 在其四级结构和伴侣特性上明显不同，定义了第二种细菌二组分 sHsps 系统。
