Promiscuous substrate recognition in folding and assembly activities of the trigger factor chaperone

Area of Science:

• Bacterial protein synthesis and folding
• Molecular chaperones and protein homeostasis

Background:

• Trigger factor (TF) is a bacterial molecular chaperone known to interact with nascent polypeptide chains on ribosomes.
• The activity and substrate specificity of ribosome-free TF in the cytosol remain less characterized.
• In vitro studies suggest TF's role in promoting protein refolding.

Purpose of the Study:

• To investigate the function of ribosome-free TF in the bacterial cytosol.
• To identify the range of full-length proteins that interact with and are rescued by cytosolic TF.
• To elucidate the structural basis of TF's interaction with a physiological substrate.

Main Methods:

• Proteomic analysis to identify cytosolic TF substrates in Escherichia coli.
• Biochemical characterization of a TF:S7 complex from Thermotoga maritima.
• X-ray crystallography to determine the atomic structure of the TF:S7 complex.

Main Results:

• Ribosome-free TF stably associates with and rescues over 170 full-length proteins from misfolding.
• Ribosomal protein S7 was identified as a cytosolic TF substrate.
• The crystal structure of the TF:S7 complex provides atomic-level insight into substrate recognition and chaperone mechanism.

Conclusions:

• Cytosolic TF possesses a broad substrate repertoire, acting as a promiscuous chaperone.
• TF plays a significant role in maintaining protein homeostasis and preventing misfolding in the bacterial cytosol.
• The TF:S7 complex structure reveals mechanisms for substrate binding and suggests TF's involvement in protein complex biogenesis.