DegP Chaperone Suppresses Toxic Inner Membrane Translocation Intermediates

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Pathogenesis

Background:

• Gram-negative bacteria utilize periplasmic molecular chaperones for protein folding and targeting.
• DegP, a protease, also functions as a chaperone in the periplasmic quality control network.
• Autotransporter virulence proteins, like pertactin, require proper folding and secretion pathways.

Purpose of the Study:

• To investigate the role of DegP in the secretion and folding of the Bordetella pertussis autotransporter pertactin.
• To elucidate the connection between DegP's chaperone activity and protein translocation across the inner membrane (IM).
• To understand the mechanism by which DegP prevents toxicity during protein secretion.

Main Methods:

• Utilized Escherichia coli ΔdegP strains for studying pertactin production.
• Manipulated signal sequences of pertactin to alter inner membrane translocation timing (co-translational vs. post-translational).
• Assessed bacterial growth, periplasmic protein levels, and stress response indicators (soluble σE).

Main Results:

• Pertactin production was lethal in E. coli lacking DegP, indicating a critical role for DegP.
• DegP's chaperone activity restored bacterial growth during pertactin production.
• An E. coli signal sequence promoting co-translational IM translocation suppressed lethality, while a post-translational signal sequence recapitulated the lethal phenotype.
• Lethality correlated with the loss of periplasmic proteins and the σE stress response.

Conclusions:

• DegP's chaperone function is essential for preventing lethal protein misfolding during the secretion of certain proteins.
• The mechanism of protein translocation across the inner membrane (co-translational vs. post-translational) significantly impacts the requirement for DegP.
• Post-translational translocation can generate toxic periplasmic folding intermediates that DegP actively suppresses.