A redox switch shapes the Lon protease exit pore to facultatively regulate proteolysis

Area of Science:

• Biochemistry
• Molecular Biology
• Microbiology

Background:

• The Lon AAA+ protease degrades misfolded proteins but its environmental regulation is unknown.
• Facultative anaerobic bacteria like Enterobacteriaceae adapt to both aerobic and anaerobic conditions.
• Bacterial Lon proteases possess unique surface cysteine residues forming a disulfide bond.

Purpose of the Study:

• To investigate the regulatory mechanism of Lon AAA+ protease activity in response to environmental changes.
• To elucidate the role of cysteine residues and disulfide bonds in Lon protease function.

Main Methods:

• Structural analysis of the Lon protease P-domain.
• Biochemical assays to measure protease activity.
• Redox potential measurements.

Main Results:

• The two cysteine residues on the Lon protease P-domain surface form a redox-sensitive disulfide bond.
• Disulfide bond reduction narrows the P-domain exit pore by ~30%, decreasing protease activity by 80%.
• Oxidation restores pore size and activity, with a redox switch potential (E°' = -227 mV) tuned to environmental oxygen levels.

Conclusions:

• Bacterial Lon protease activity is regulated by a redox switch involving cysteine residues.
• This switch optimizes cellular proteolysis levels for different oxygen environments (anaerobic vs. aerobic).
• The findings reveal a novel mechanism for environmental adaptation in bacteria.