Université de Lyon, F69003, Université Lyon 1, F69622, INSA-Lyon F69621, France.
J Bacteriol. 2012 Nov;194(22):6131-42. doi: 10.1128/JB.01419-12. Epub 2012 Sep 7.
The twin arginine translocation (Tat) pathway exports folded proteins from the cytoplasm to the periplasm of bacteria. The targeting of the exported proteins to the Tat pathway relies on a specific amino-terminal signal sequence, which is cleaved after exportation. In the phytopathogen Dickeya dadantii, the pectin lyase homologue PnlH is exported by the Tat pathway without cleavage of its signal sequence, which anchors PnlH into the outer membrane. In proteobacteria, the vast majority of outer membrane proteins consists of β-barrel proteins and lipoproteins. Thus, PnlH represents a new kind of outer membrane protein. In Escherichia coli, periplasmic chaperones SurA, Skp, and DegP work together with the β-barrel assembly machinery (Bam) to target and insert β-barrel proteins into the outer membrane. In this work, we showed that SurA is required for an efficient targeting of PnlH to the outer membrane. Moreover, we were able to detect an in vitro interaction between SurA and the PnlH signal sequence. Since the PnlH signal sequence contains a highly hydrophobic region, we propose that SurA protects it from the hydrophobic periplasm during targeting of PnlH to the outer membrane. We also studied the nature of the information carried by the PnlH signal sequence responsible for its targeting to the outer membrane after exportation by the Tat system.
双精氨酸转运（Tat）途径将折叠的蛋白质从细胞质输出到细菌的周质中。输出蛋白质到 Tat 途径的靶向依赖于特定的氨基末端信号序列，该序列在输出后被切割。在植物病原体迪基氏菌（Dickeya dadantii）中，果胶裂解酶同源物 PnlH 通过 Tat 途径输出，其信号序列不被切割，从而将 PnlH 锚定在外膜上。在变形菌中，绝大多数外膜蛋白由β-桶蛋白和脂蛋白组成。因此，PnlH 代表了一种新型的外膜蛋白。在大肠杆菌中，周质伴侣蛋白 SurA、Skp 和 DegP 与β-桶组装机制（Bam）一起作用，将β-桶蛋白靶向并插入外膜中。在这项工作中，我们表明 SurA 是 PnlH 有效靶向外膜所必需的。此外，我们能够检测到 SurA 与 PnlH 信号序列之间的体外相互作用。由于 PnlH 信号序列包含一个高度疏水的区域，我们提出 SurA 在将 PnlH 靶向外膜时保护它免受疏水环境的影响。我们还研究了 PnlH 信号序列所携带的信息的性质，这些信息负责在 Tat 系统输出后将其靶向到外膜。
