Gan Yong-Liang, Yang Li-Yan, Yang Li-Chao, Li Wan-Lian, Liang Xue-Lian, Jiang Wei, Jiang Guo-Feng, Hang Xiao-Hong, Yang Mei, Tang Ji-Liang, Jiang Bo-Le
State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, Nanning, China.
College of Forest, Guangxi University, Nanning, China.
PLoS One. 2021 Jan 28;16(1):e0246033. doi: 10.1371/journal.pone.0246033. eCollection 2021.
Many animal and plant pathogenic bacteria employ a type three secretion system (T3SS) to deliver type three effector proteins (T3Es) into host cells. Efficient secretion of many T3Es in the plant pathogen Xanthomonas campestris pv. campestris (Xcc) relies on the global chaperone HpaB. However, how the domain of HpaB itself affects effector translocation/secretion is poorly understood. Here, we used genetic and biochemical approaches to identify a novel domain at the C-terminal end of HpaB (amino acid residues 137-160) that contributes to virulence and hypersensitive response (HR). Both in vitro secretion assay and in planta translocation assay showed that the secretion and translocation of T3E proteins depend on the C-terminal region of HpaB. Deletion of the C-terminal region of HpaB did not affect binding to T3Es, self-association or interaction with T3SS components. However, the deletion of C-terminal region sharply reduced the mounts of free T3Es liberated from the complex of HpaB with the T3Es, a reaction catalyzed in an ATP-dependent manner by the T3SS-associated ATPase HrcN. Our findings demonstrate the C-terminal domain of HpaB contributes to disassembly of chaperone-effector complex and reveal a potential molecular mechanism underpinning the involvement of HpaB in secretion of T3Es in Xcc.
许多动植物致病细菌利用三型分泌系统（T3SS）将三型效应蛋白（T3Es）输送到宿主细胞中。植物病原菌野油菜黄单胞菌野油菜致病变种（Xcc）中许多T3Es的有效分泌依赖于全局伴侣蛋白HpaB。然而，HpaB自身的结构域如何影响效应蛋白的转运/分泌却知之甚少。在这里，我们使用遗传学和生物化学方法在HpaB的C末端鉴定了一个新的结构域（氨基酸残基137 - 160），该结构域对毒力和过敏反应（HR）有贡献。体外分泌试验和植物体内转运试验均表明，T3E蛋白的分泌和转运依赖于HpaB的C末端区域。删除HpaB的C末端区域并不影响其与T3Es的结合、自我缔合或与T3SS组件的相互作用。然而，C末端区域的缺失显著减少了从HpaB与T3Es的复合物中释放的游离T3Es的量，这一反应由T3SS相关的ATP酶HrcN以ATP依赖的方式催化。我们的研究结果表明，HpaB的C末端结构域有助于伴侣蛋白 - 效应蛋白复合物的解离，并揭示了HpaB参与Xcc中T3Es分泌的潜在分子机制。
