Covalent modification of proteins by mixed-function oxidation: recognition by intracellular proteases

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Mixed-function oxidation is a site-specific reaction modifying E. coli glutamine synthetase.
• This modification leads to catalytic inactivation and loss of a histidine residue, likely at a metal-binding site.

Purpose of the Study:

• To investigate the mechanism and implications of oxidative modification of E. coli glutamine synthetase.
• To explore the role of oxidative modification in protein degradation and cellular processes.

Main Methods:

• Studied the effects of mixed-function oxidation on E. coli glutamine synthetase activity and structure.
• Assessed the susceptibility of oxidatively modified glutamine synthetase to proteolytic attack.
• Compared oxidative modification with other inactivation methods like adenylylation.

Main Results:

• Oxidative modification results in catalytic inactivation and increased susceptibility to proteolysis.
• Proteases preferentially degrade the oxidatively modified enzyme, similar to major structural changes.
• Adenylylation, unlike oxidation, does not affect proteolysis rates.

Conclusions:

• E. coli glutamine synthetase degradation likely involves a two-step process initiated by oxidative inactivation.
• Oxidative modification may serve as a general signal for protein degradation in vivo.
• This mechanism could be involved in protein turnover, host defense, and aging processes.