Dynamic Behavior of Trigger Factor on the Ribosome.

Area of Science:

• Bacterial protein synthesis and folding
• Molecular chaperones
• Ribosome-nascent chain complexes

Background:

• Trigger factor (TF) is the sole ribosome-associated chaperone in bacteria.
• TF interacts with hydrophobic segments of nascent chains (NCs) emerging from the ribosome.
• TF's N-terminal ribosome-binding domain (RBD) binds to ribosomal protein uL23.

Purpose of the Study:

• To investigate the flexibility of TF when bound to the ribosome.
• To elucidate the structural dynamics of TF during nascent chain elongation.
• To understand the molecular basis of TF's chaperone activity.

Main Methods:

• Cryo-electron microscopy (cryo-EM) of TF bound to translating ribosomes.
• Structural analysis of TF-ribosome complexes with varying nascent chain lengths.
• Molecular dynamics (MD) simulations to complement structural data.

Main Results:

• Two distinct cryo-EM structures of TF bound to E. coli ribosomes were determined.
• Distinct domain flexibility within TF was observed, with a conformational rearrangement of the RBD upon ribosome binding.
• Increased rigidity of TF was noted as the nascent chain extended.
• MD simulations supported the observed structural dynamics and provided a molecular explanation.

Conclusions:

• Bacterial TF is a flexible chaperone, not a rigid molecule as previously thought.
• TF undergoes conformational changes upon ribosome binding and nascent chain extension.
• These dynamics are crucial for TF's function in protein folding and preventing aggregation.