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首页> 外文期刊>Journal of bacteriology >Proteolytic Cleavage of the FlhB Homologue YscU of Yersinia pseudotuberculosis Is Essential for Bacterial Survival but Not for Type III Secretion
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Proteolytic Cleavage of the FlhB Homologue YscU of Yersinia pseudotuberculosis Is Essential for Bacterial Survival but Not for Type III Secretion

机译：蛋白水解裂解的耶尔森氏菌假单胞菌的FlhB同源YscU是细菌生存所必需的，但对于III型分泌不是必需的。

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Pathogenic Yersinia species employ a type III secretion system (TTSS) to target antihost factors, Yop proteins, into eukaryotic cells. The secretion machinery is constituted of ca. 20 Ysc proteins, nine of which show significant homology to components of the flagellar TTSS. A key event in flagellar assembly is the switch from secreting-assembling hook substrates to filament substrates, a switch regulated by FlhB and FliK. The focus of this study is the FlhB homologue YscU, a bacterial inner membrane protein with a large cytoplasmic C-terminal domain. Our results demonstrate that low levels of YscU were required for functional Yop secretion, whereas higher levels of YscU lowered both Yop secretion and expression. Like FlhB, YscU was cleaved into a 30-kDa N-terminal and a 10-kDa C-terminal part. Expression of the latter in a wild-type strain resulted in elevated Yop secretion. The site of cleavage was at a proline residue, within the strictly conserved amino acid sequence NPTH. A YscU protein with an in-frame deletion of NPTH was cleaved at a different position and was nonfunctional with respect to Yop secretion. Variants of YscU with single substitutions in the conserved NPTH sequence—i.e., N263A, P264A, or T265A—were not cleaved but retained function in Yop secretion. Elevated expression of these YscU variants did, however, result in severe growth inhibition. From this we conclude that YscU cleavage is not a prerequisite for Yop secretion but is rather required to maintain a nontoxic fold.
机译：致病性耶尔森氏菌物种采用III型分泌系统（TTSS）将抗宿主因子Yop蛋白靶向真核细胞。分泌机由大约20个Ysc蛋白，其中9个与鞭毛TTSS的成分具有显着同源性。鞭毛组装中的关键事件是从秘密组装的钩形基板转换为细丝基板，这是由FlhB和FliK调节的转换。这项研究的重点是FlhB同源物YscU，一种具有大细胞质C末端结构域的细菌内膜蛋白。我们的结果表明，低水平的YscU是功能性Yop分泌所必需的，而较高水平的YscU会降低Yop的分泌和表达。像FlhB一样，YscU被切割成30kDa的N末端和10kDa的C末端部分。后者在野生型菌株中的表达导致Yop分泌增加。裂解位点在脯氨酸残基，在严格保守的氨基酸序列NPTH内。具有NPTH框内缺失的YscU蛋白在不同位置被切割，并且相对于Yop分泌是无功能的。保守的NPTH序列中具有单取代的YscU变体（即N263A，P264A或T265A）未被切割，但在Yop分泌中保留了功能。但是，这些YscU变体的表达升高确实导致了严重的生长抑制。据此我们得出结论，YscU裂解不是Yop分泌的前提，而是维持无毒折叠的必要条件。

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