Dataset Information

Heat shock transcription factor ?32 co-opts the signal recognition particle to regulate protein homeostasis in E. coli.

ABSTRACT: All cells must adapt to rapidly changing conditions. The heat shock response (HSR) is an intracellular signaling pathway that maintains proteostasis (protein folding homeostasis), a process critical for survival in all organisms exposed to heat stress or other conditions that alter the folding of the proteome. Yet despite decades of study, the circuitry described for responding to altered protein status in the best-studied bacterium, E. coli, does not faithfully recapitulate the range of cellular responses in response to this stress. Here, we report the discovery of the missing link. Surprisingly, we found that ?(32), the central transcription factor driving the HSR, must be localized to the membrane rather than dispersed in the cytoplasm as previously assumed. Genetic analyses indicate that ?(32) localization results from a protein targeting reaction facilitated by the signal recognition particle (SRP) and its receptor (SR), which together comprise a conserved protein targeting machine and mediate the cotranslational targeting of inner membrane proteins to the membrane. SRP interacts with ?(32) directly and transports it to the inner membrane. Our results show that ?(32) must be membrane-associated to be properly regulated in response to the protein folding status in the cell, explaining how the HSR integrates information from both the cytoplasm and bacterial cell membrane.

SUBMITTER: Lim B

PROVIDER: S-EPMC3866087 | biostudies-literature | 2013 Dec

REPOSITORIES: biostudies-literature

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Heat shock transcription factor σ32 co-opts the signal recognition particle to regulate protein homeostasis in E. coli.

Lim Bentley B Miyazaki Ryoji R Neher Saskia S Siegele Deborah A DA Ito Koreaki K Walter Peter P Akiyama Yoshinori Y Yura Takashi T Gross Carol A CA

PLoS biology 20131217 12

All cells must adapt to rapidly changing conditions. The heat shock response (HSR) is an intracellular signaling pathway that maintains proteostasis (protein folding homeostasis), a process critical for survival in all organisms exposed to heat stress or other conditions that alter the folding of the proteome. Yet despite decades of study, the circuitry described for responding to altered protein status in the best-studied bacterium, E. coli, does not faithfully recapitulate the range of cellula ...[more]

PMID: 24358019

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Project description:Correct targeting of membrane proteins is essential for membrane integrity, cell physiology, and viability. Cotranslational targeting depends on the universally conserved signal recognition particle (SRP), which is a ribonucleoprotein complex comprised of the protein component Ffh and the 4.5S RNA in Escherichia coli About 25?years ago it was reported that Ffh is an unstable protein, but the underlying mechanism has never been explored. Here, we show that Lon is the primary protease responsible for adjusting the cellular Ffh level. When overproduced, Ffh is particularly prone to degradation during transition from exponential to stationary growth and the cellular Ffh amount is lowest in stationary phase. The Ffh protein consists of two domains, the NG domain, responsible for GTP hydrolysis and docking to the membrane receptor FtsY, and the RNA-binding M domain. We find that the NG domain alone is stable, whereas the isolated M domain is degraded. Consistent with the importance of Lon in this process, the M domain confers synthetic lethality to the lon mutant. The Ffh homolog from the model plant Arabidopsis thaliana, which forms a protein-protein complex rather than a protein-RNA complex, is stable, suggesting that the RNA-binding ability residing in the M domain of E. coli Ffh is important for proteolysis. Our results support a model in which excess Ffh not bound to 4.5S RNA is subjected to proteolysis until an appropriate Ffh concentration is reached. The differential proteolysis adjusts Ffh levels to the cellular demand and maintains cotranslational protein transport and membrane integrity.IMPORTANCE Since one-third of all bacterial proteins reside outside the cytoplasm, protein targeting to the appropriate address is an essential process. Cotranslational targeting to the membrane relies on the signal recognition particle (SRP), which is a protein-RNA complex in bacteria. We report that the protein component Ffh is a substrate of the Lon protease. Regulated proteolysis of Ffh provides a simple mechanism to adjust the concentration of the essential protein to the cellular demand. This is important because elevated or depleted SRP levels negatively impact protein targeting and bacterial fitness.

Dataset Information

Heat shock transcription factor ?32 co-opts the signal recognition particle to regulate protein homeostasis in E. coli.

Publications

Heat shock transcription factor σ32 co-opts the signal recognition particle to regulate protein homeostasis in E. coli.

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