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首页> 外文期刊>Journal of Molecular Biology >Functional defect and restoration of temperature-sensitive mutants of flha, a subunit of the flagellar protein export apparatus
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Functional defect and restoration of temperature-sensitive mutants of flha, a subunit of the flagellar protein export apparatus

机译：flha（鞭毛蛋白输出装置的一个亚基）的温度敏感性突变体的功能缺陷和恢复

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摘要

The flagellar axial component proteins are exported to the distal end of the growing flagellum for self-assembly by the flagellar type III export apparatus. FlhA is a key membrane protein of the export apparatus, and its C-terminal cytoplasmic domain (FlhA C) is a part of an assembly platform for the three soluble export components, FliH, FliI, and FliJ, as well as export substrates and chaperone-substrate complexes. FlhA C is composed of a flexible linker region and four compact domains (A CD1-A CD4). At 42 °C, a temperature-sensitive (TS) G368C mutation in FlhA C blocks the export process after the FliH-FliI-FliJ-substrate complex binds to the assembly platform, but it remains unknown how it does so. In this study, we analyzed a TS mutant variant, FlhA C(G368C), and its pseudorevertant variants FlhA C(G368C/L359F), FlhA C(G368C/G364R), FlhA C(G368C/R370S), and FlhA C(G368C/P550S) using far-ultraviolet circular dichroism. Whereas the denaturation of the wild-type FlhA C occurs in a single step, FlhA C(G368C) and its pseudorevertant variants showed thermal transitions, at least, in two steps. The first transition of FlhA C(G368C) can further be divided into reversible and following irreversible transitions, which correspond to the denaturation of A CD2 and A CD1, respectively. We show the relation between the reversible transition and the TS defect in the exporting function of FlhA C(G368C) and that the loss of function is caused by denaturation of A CD2. We suggest that A CD2 is directly involved in the translocation of export substrates.
机译：鞭毛的轴向成分蛋白通过鞭毛III型输出设备输出到正在生长的鞭毛的远端，以便自组装。 FlhA是出口设备的关键膜蛋白，其C端胞质结构域（FlhA C）是FliH，FliI和FliJ三种可溶性出口成分以及出口底物和分子伴侣的装配平台的一部分。 -底物复合物。 FlhA C由柔性接头区和四个紧凑域（A CD1-A CD4）组成。在42°C时，FliH-FliI-FliJ-底物复合物结合到组装平台后，FlhA C中的温度敏感（TS）G368C突变阻止了出口过程，但如何进行仍是未知的。在这项研究中，我们分析了TS突变体FlhA C（G368C）及其假回复变体FlhA C（G368C / L359F），FlhA C（G368C / G364R），FlhA C（G368C / R370S）和FlhA C（G368C） / P550S）使用远紫外圆二色性。野生型FlhA C的变性是一步完成的，而FlhA C（G368C）及其假回复变体至少在两个步骤中显示出热转变。 FlhA C（G368C）的第一个转变可以进一步分为可逆转变和随后的不可逆转变，分别对应于A CD2和A CD1的变性。我们显示了FlhA C（G368C）的出口功能中可逆转变与TS缺陷之间的关系，并且功能丧失是由A CD2变性引起的。我们建议A CD2直接参与出口底物的易位。

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