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Ligand crowding at a nascent signal sequence.

Gottfried Eisner1, Hans-Georg Koch, Konstanze Beck

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The signal sequence of E. coli secretory proteins interacts with ribosomal protein L23 and chaperones like Trigger Factor (TF) as it emerges from the ribosome. TF sequesters the signal sequence, potentially controlling its access to other proteins.

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Area of Science:

  • Molecular biology
  • Protein folding
  • Bacterial protein secretion

Background:

  • The signal sequence directs secretory proteins to their destinations.
  • Understanding its early interactions is crucial for protein secretion.
  • Escherichia coli provides a model system for studying these processes.

Purpose of the Study:

  • To systematically analyze the molecular environment of the pOmpA signal sequence during its emergence from the ribosome.
  • To investigate the role of chaperones and ribosomal proteins in this process.
  • To determine how these interactions change with nascent chain growth.

Main Methods:

  • Stage- and site-specific cross-linking in Escherichia coli.
  • Analysis of protein-protein interactions involving the pOmpA signal sequence.
  • Investigating the influence of the Trigger Factor (TF) chaperone.

Main Results:

  • The pOmpA signal sequence initially contacts ribosomal protein L23, Ffh (signal recognition particle), and SecA.
  • As the nascent chain grows, the signal sequence becomes sequestered by Trigger Factor (TF).
  • TF's absence leads to prolonged interactions with L23 and Ffh, but not SecB.

Conclusions:

  • The signal sequence of E. coli secretory proteins undergoes dynamic changes in its molecular environment upon ribosomal exit.
  • Trigger Factor (TF) plays a key role in sequestering the signal sequence, modulating its accessibility.
  • These findings provide insights into the regulation of bacterial protein secretion.