Matson Jyl S, DiRita Victor J
Department of Microbiology and Immunology and Unit for Laboratory Animal Medicine, University of Michigan Medical School, Ann Arbor, MI 48109-0620, USA.
Proc Natl Acad Sci U S A. 2005 Nov 8;102(45):16403-8. doi: 10.1073/pnas.0505818102. Epub 2005 Oct 27.
A common mechanism inhibiting the activity of transcription factors is their sequestration to the membrane until they are needed, at which point they are released from the membrane by proteolysis. Acting in contrast to this inhibition mechanism are virulence regulators of Vibrio cholerae, the ToxR and TcpP proteins, which are localized to the inner membrane of the cell, where they bind promoter DNA and activate gene expression. TcpP is rapidly degraded in the absence of another protein, TcpH. We used a genetic screen to identify regulators of TcpP stability and identified the YaeL membrane-localized zinc metalloprotease as responsible for degrading TcpP in the absence of TcpH. In Escherichia coli, DegS and YaeL cooperate to degrade RseA, an antisigma factor that sequesters sigma(E) to the inner membrane, thereby inhibiting the activity of sigma(E). When yaeL was disrupted in a V. cholerae tcpH mutant, we observed accumulation of a lower molecular weight species of TcpP. This observation is consistent with TcpP being partially degraded in the absence of YaeL. A mutant lacking both DegS and YaeL continued to accumulate the TcpP degradation product, indicating that protease other than DegS is acting before YaeL in degrading TcpP. The YaeL-dependent degradation pathway is active in TcpH(+) cells under conditions that are not favorable for virulence gene activation. This work expands the knowledge of YaeL-dependent processing in the bacterial cell and reveals an unexpected layer of virulence gene regulation in V. cholerae.
抑制转录因子活性的一种常见机制是将它们隔离在膜上,直到需要时,此时它们通过蛋白水解作用从膜上释放出来。与这种抑制机制相反的是霍乱弧菌的毒力调节因子,即ToxR和TcpP蛋白,它们定位于细胞内膜,在那里它们结合启动子DNA并激活基因表达。在没有另一种蛋白质TcpH的情况下,TcpP会迅速降解。我们通过遗传筛选来鉴定TcpP稳定性的调节因子,并确定膜定位的锌金属蛋白酶YaeL在没有TcpH的情况下负责降解TcpP。在大肠杆菌中,DegS和YaeL协同作用降解RseA,RseA是一种抗σ因子,它将σ(E)隔离在内膜上,从而抑制σ(E)的活性。当在霍乱弧菌tcpH突变体中破坏yaeL时,我们观察到一种分子量较低的TcpP物种的积累。这一观察结果与TcpP在没有YaeL的情况下被部分降解是一致的。同时缺乏DegS和YaeL的突变体继续积累TcpP降解产物,这表明除DegS之外的蛋白酶在YaeL之前参与降解TcpP。在不利于毒力基因激活的条件下,YaeL依赖性降解途径在TcpH(+)细胞中是活跃的。这项工作扩展了对细菌细胞中YaeL依赖性加工的认识,并揭示了霍乱弧菌中毒力基因调控的一个意想不到的层面。