The dynamics of SecM-induced translational stalling

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• SecM acts as an Escherichia coli (E. coli) secretion monitor, stalling translation on prokaryotic ribosomes without requiring cofactors.
• Previous studies showed SecM's nascent chain interacts with the 50S subunit exit tunnel, inhibiting peptide bond formation.
• The precise dynamics and pathways of SecM-mediated stalling on mRNA remained largely undefined.

Purpose of the Study:

• To elucidate the dynamic mechanism and timescales of SecM-mediated translational stalling.
• To investigate the role of peptide-ribosome interactions in controlling translation elongation.

Main Methods:

• Employed single-molecule fluorescence techniques to directly track ribosome elongation dynamics.
• Focused on ribosomes translating the specific SecM stall sequence (FSTPVWISQAQGIRAGP).

Main Results:

• Observed cooperative peptide-ribosome interactions involving three distinct interactions within the last five codons of SecM.
• Demonstrated severely impaired elongation rates, commencing at the terminal proline and persisting for four codons.
• Characterized these interactions occurring within a 1-minute timeframe.

Conclusions:

• Translational stalling by SecM is intrinsically linked to the dynamic processes of translation elongation.
• The 50S ribosomal subunit exit tunnel and the nascent SecM chain play critical roles in regulating fundamental translation steps.
• Provides a dynamic model for SecM-mediated translational arrest.