In Salmonella enterica, 2-methylcitrate blocks gluconeogenesis

Area of Science:

• Microbiology
• Metabolic Biochemistry

Background:

• Salmonella enterica serovar Typhimurium LT2 strains deficient in the 2-methylcitric acid cycle (2-MCC) exhibit heightened propionate sensitivity.
• This sensitivity is partly attributed to 2-methylcitrate (2-MC) generated by citrate synthase (GltA) from the Krebs cycle.

Purpose of the Study:

• To identify the molecular target of 2-MC produced by GltA in Salmonella.
• To elucidate the mechanism of propionate toxicity in 2-MCC deficient strains.
• To explore strategies for overcoming this toxicity.

Main Methods:

• In vivo and in vitro assays were performed.
• Fructose-1,6-bisphosphatase (FBPase) activity was assessed.
• Genetic manipulation of FBPase was employed.
• Comparative toxicity studies of different 2-MC isomers were conducted.

Main Results:

• 2-MC produced by GltA (2-MC(GltA)) directly inhibits fructose-1,6-bisphosphatase (FBPase), a key gluconeogenesis enzyme.
• Increased FBPase levels or micromolar glucose concentrations rescued growth inhibition.
• A specific FBPase mutation (S123F) conferred resistance to 2-MC(GltA).
• 2-MC(GltA) was significantly more toxic than 2-MC produced by PrpC (2-MC(PrpC)).

Conclusions:

• GltA-derived 2-MC inhibits FBPase, causing propionate sensitivity in Salmonella lacking the 2-MCC.
• The differential toxicity of 2-MC isomers suggests GltA produces non-metabolizable isomers that disrupt FBPase.
• These findings offer insights into propionate metabolism disorders and potential therapeutic targets.