Degradation of the membrane-localized virulence activator TcpP by the YaeL protease in Vibrio cholerae.

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.