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

Abstract

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 E to the inner membrane, thereby inhibiting the activity of 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.gene regulation ͉ pathogenesis ͉ membrane regulators

Bile salt–induced intermolecular disulfide bond formation activates Vibrio cholerae virulence

“…S3B). We found that bile salts had no effect on TcpP stability, and that TcpA protein production was dependent on the presence of TcpH only if YaeL was also present, as has been previously reported (14).…”

“…2C). TcpP is known to be rapidly degraded through proteolysis by the protease YaeL in the absence of a second protective protein, TcpH (14). To test whether bile salts affect TcpP stability through TcpH, we examined the bile salt effects on TcpP stability ( Fig.…”

Design principles of the proteolytic cascade governing the σE-mediated envelope stress response in Escherichia coli: keys to graded, buffered, and rapid signal transduction

“…We have suggested that RseP cleavage of full-length RseA is blocked so that DegS cleavage of RseA will be rate-limiting over a wide range of OMP signal. Interestingly, other RIP proteases that are widely used to transmit signals via a protease cascade between the compartments of a bacterial cell appear to occupy an intermediate position in every cascade: They transmit the signal rather than initiate the cascade and their activity is inhibited until the initial cleavage event is completed (Schobel et al 2004;Chen et al 2005;Matson and DiRita 2005). Cells use widely different proteins to accomplish inhibition; it remains an open question as to whether these inhibitory events are mechanistically similar or distinct (Resnekov and Losick 1998;Dong and Cutting 2003;Kroos 2004, 2005).…”

Formation of an Intramolecular Periplasmic Disulfide Bond in TcpP Protects TcpP and TcpH from Degradation in Vibrio cholerae

“…TcpPH, along with constitutively expressed ToxRS, activates transcription of toxT, resulting in colonization and CT secretion in a temporally coordinated fashion (13). Under noninducing conditions, TcpP is specifically targeted for degradation by the site 1 periplasmic protease, Tsp, followed by the membrane-localized metalloprotease YaeL (10,14,24).TcpP and ToxR have three distinct domains: an N-terminal cytoplasmic DNA-binding domain, a single membrane-spanning domain, and a C-terminal periplasmic domain. The cytoplasmic domain of TcpP and ToxR is homologous to that of the OmpR/ PhoB family of w-HTH transcription factors (15).…”