The quorum sensing regulator HapR downregulates the expression of the virulence gene transcription factor AphA in Vibrio cholerae by antagonizing Lrp- and VpsR-mediated activation
The quorum sensing regulator HapR downregulates the expression of the virulence gene transcription factor AphA in Vibrio cholerae by antagonizing Lrp- and VpsR-mediated activation
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DOI：
10.1111/j.1365-2958.2007.05693.x
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发表时间：
2007-05-01
影响因子：
3.6
通讯作者：
Skorupski, Karen
中科院分区：
文献类型：
--
作者：
Lin, Wei;Kovacikova, Gabriela;Skorupski, Karen
HapR 是一种群体感应调节转录因子，通过与 aphA 启动子中以 -71 为中心的特定位点结合来抑制霍乱弧菌中的毒力级联，最终阻止弧菌致病岛上 tcpPH 启动子的激活。为了阐明 HapR 抑制 aphA 表达的机制，我们鉴定了两个转录调节因子 Lrp 和 VpsR，它们都激活 aphA 启动子。 Lrp 是亮氨酸响应性调节蛋白，与启动子中 -136 和 -123 之间的区域结合以启动 aphA 表达。 VpsR 是控制生物膜形成的反应调节因子，与 -123 和 -73 之间的区域结合以激活 aphA 表达。 HapR 通过拮抗这两种激活剂的功能来抑制 aphA 表达。 -71 处的 HapR 结合位点位于 Lrp 结合位点下游并与 VpsR 结合位点重叠。 HapR 结合因此直接阻断 VpsR 接近启动子。 aphA 启动子 (G-77T) 中天然存在的点突变先前已被证明可以阻止 HapR 结合，也可以阻止 VpsR 结合。在缺乏 HapR 的情况下，Lrp 或 VpsR 都能够实现 aphA 启动子的几乎完全表达，但当它们一起存在时，它们的作用在某种程度上是相加的。 aphA 启动子也是负向自动调节的，AphA 结合位点集中在 -20。这里的结果提供了 Lrp 和 VpsR 对 aphA 启动子的双重激活以及 HapR 和 AphA 的双重抑制的模型。
HapR is a quorum sensing-regulated transcription factor that represses the virulence cascade in Vibrio cholerae by binding to a specific site centred at -71 in the aphA promoter, ultimately preventing activation of the tcpPH promoter on the Vibrio pathogenicity island. In an effort to elucidate the mechanism by which HapR represses aphA expression, we identified two transcriptional regulators, Lrp and VpsR, both of which activate the aphA promoter. Lrp, the leucine-responsive regulatory protein, binds to a region between -136 and -123 in the promoter to initiate aphA expression. VpsR, the response regulator that controls biofilm formation, binds to a region between -123 and -73 to activate aphA expression. HapR represses aphA expression by antagonizing the functions of both of these activators. The HapR binding site at -71 lies downstream of the Lrp binding site and overlaps the VpsR binding site. HapR binding thus directly blocks access of VpsR to the promoter. A naturally occurring point mutation in the aphA promoter (G-77T), which has previously been shown to prevent HapR binding, also prevents VpsR binding. In the absence of HapR, either Lrp or VpsR is capable of achieving nearly full expression of the aphA promoter, but when present together their effects are to some degree additive. The aphA promoter is also negatively autoregulated and an AphA binding site is centred at -20. The results here provide a model for the dual activation of the aphA promoter by Lrp and VpsR as well as its dual repression by HapR and AphA.