In Salmonella enterica, 2-methylcitrate blocks gluconeogenesis.
Strains of Salmonella enterica serovar Typhimurium LT2 lacking a functional 2-methylcitric acid cycle (2-MCC) display increased sensitivity to propionate. Previous work from our group indicated that this sensitivity to propionate is in part due to the production of 2-methylcitrate (2-MC) by the Krebs cycle enzyme citrate synthase (GltA). Here we report in vivo and in vitro data which show that a target of the 2-MC isomer produced by GltA (2-MC(GltA)) is fructose-1,6-bisphosphatase (FBPase), a key enzyme in gluconeogenesis. Lack of growth due to inhibition of FBPase by 2-MC(GltA) was overcome by increasing the level of FBPase or by micromolar amounts of glucose in the medium. We isolated an fbp allele encoding a single amino acid substitution in FBPase (S123F), which allowed a strain lacking a functional 2-MCC to grow in the presence of propionate. We show that the 2-MC(GltA) and the 2-MC isomer synthesized by the 2-MC synthase (PrpC; 2-MC(PrpC)) are not equally toxic to the cell, with 2-MC(GltA) being significantly more toxic than 2-MC(PrpC). This difference in 2-MC toxicity is likely due to the fact that as a si-citrate synthase, GltA may produce multiple isomers of 2-MC, which we propose are not substrates for the 2-MC dehydratase (PrpD) enzyme, accumulate inside the cell, and have deleterious effects on FBPase activity. Our findings may help explain human inborn errors in propionate metabolism.
Rocco
Christopher J
CJ
Department of Bacteriology, University of Wisconsin, 1550 Linden Dr., Madison, WI 53706-1521, USA.
Escalante-Semerena
Jorge C
JC
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002950:Citrate (si)-Synthase / Q000235:genetics / Q000378:metabolism; D002951:Citrates / Q000494:pharmacology*; D006597:Fructose-Bisphosphatase / Q000378:metabolism / Q000502:physiology; D005943:Gluconeogenesis / Q000187:drug effects*; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology; D006836:Hydro-Lyases / Q000235:genetics / Q000378:metabolism; D008954:Models, Biological; D011422:Propionates / Q000494:pharmacology; D019779:Salmonella enterica / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*
D001426:Bacterial Proteins; D002951:Citrates; D011422:Propionates; C031605:2-methylcitric acid; D002950:Citrate (si)-Synthase; D006597:Fructose-Bisphosphatase; C092884:methylcitrate synthase; D006836:Hydro-Lyases; D005947:Glucose