Astbury Centre for Structural Molecular Biology, School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, UK.
Astbury Centre for Structural Molecular Biology, School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, UK.
J Mol Biol. 2019 Mar 15;431(6):1267-1283. doi: 10.1016/j.jmb.2019.01.032. Epub 2019 Feb 1.
SurA is a conserved ATP-independent periplasmic chaperone involved in the biogenesis of outer-membrane proteins (OMPs). Escherichia coli SurA has a core domain and two peptidylprolyl isomerase (PPIase) domains, the role(s) of which remain unresolved. Here we show that while SurA homologues in early proteobacteria typically contain one or no PPIase domains, the presence of two PPIase domains is common in SurA in later proteobacteria, implying an evolutionary advantage for this domain architecture. Bioinformatics analysis of >350,000 OMP sequences showed that their length, hydrophobicity and aggregation propensity are similar across the proteobacterial classes, ruling out a simple correlation between SurA domain architecture and these properties of OMP sequences. To investigate the role of the PPIase domains in SurA activity, we deleted one or both PPIase domains from E.coli SurA and investigated the ability of the resulting proteins to bind and prevent the aggregation of tOmpA (19 kDa) and OmpT (33 kDa). The results show that wild-type SurA inhibits the aggregation of both OMPs, as do the cytoplasmic OMP chaperones trigger factor and SecB. However, while the ability of SurA to bind and prevent tOmpA aggregation does not depend on its PPIase domains, deletion of even a single PPIase domain ablates the ability of SurA to prevent OmpT aggregation. The results demonstrate that the core domain of SurA endows its generic chaperone ability, while the presence of PPIase domains enhances its chaperone activity for specific OMPs, suggesting one reason for the conservation of multiple PPIase domains in SurA in proteobacteria.
SurA 是一种保守的 ATP 非依赖性周质伴侣，参与外膜蛋白 (OMP) 的生物发生。大肠杆菌 SurA 具有核心结构域和两个肽基脯氨酰顺反异构酶 (PPIase) 结构域，其作用尚不清楚。本文表明，早期变形菌中的 SurA 同源物通常含有一个或没有 PPIase 结构域，而在后期变形菌中 SurA 中两个 PPIase 结构域的存在很常见，这暗示了这种结构域架构的进化优势。对超过 350,000 个 OMP 序列的生物信息学分析表明，它们在整个变形菌门中的长度、疏水性和聚集倾向相似，排除了 SurA 结构域架构与 OMP 序列这些特性之间的简单相关性。为了研究 PPIase 结构域在 SurA 活性中的作用，我们从大肠杆菌 SurA 中缺失一个或两个 PPIase 结构域，并研究了产生的蛋白质结合和防止 tOmpA（19 kDa）和 OmpT（33 kDa）聚集的能力。结果表明，野生型 SurA 抑制两种 OMP 的聚集，细胞质 OMP 伴侣触发因子和 SecB 也是如此。然而，尽管 SurA 结合和防止 tOmpA 聚集的能力不依赖于其 PPIase 结构域，但即使缺失单个 PPIase 结构域也会消除 SurA 防止 OmpT 聚集的能力。结果表明，SurA 的核心结构域赋予其通用伴侣能力，而 PPIase 结构域的存在增强了其对特定 OMP 的伴侣活性，这表明在变形菌中多个 PPIase 结构域在 SurA 中保守的一个原因。
