Conserved Pyridoxal Protein That Regulates Ile and Val Metabolism

Escherichia coli YggS is a member of the highly conserved uncharacterized protein family that binds pyridoxal 5′-phosphate (PLP). To assist with the functional assignment of the YggS family,in vivo andin vitro analyses were performed using ayggS -deficientE. coli strain (ΔyggS ) and a purified form of YggS, respectively. In the stationary phase, the ΔyggS strain exhibited a completely different intracellular pool of amino acids and produced a significant amount ofl -Val in the culture medium. The log-phase ΔyggS strain accumulated 2-ketobutyrate, its aminated compound 2-aminobutyrate, and, to a lesser extent,l -Val. It also exhibited a 1.3- to 2.6-fold increase in the levels of Ile and Val metabolic enzymes. The fact that similar phenotypes were induced in wild-typeE. coli by the exogenous addition of 2-ketobutyrate and 2-aminobutyrate indicates that the 2 compounds contribute to the ΔyggS phenotypes. We showed that the initial cause of the keto acid imbalance was the reduced availability of coenzyme A (CoA); supplementation with pantothenate, which is a CoA precursor, fully reversed phenotypes conferred by theyggS mutation. The plasmid-borne expression of YggS and orthologs fromBacillus subtilis ,Saccharomyces cerevisiae , and humans fully rescued the ΔyggS phenotypes. Expression of a mutant YggS lacking PLP-binding ability, however, did not reverse the ΔyggS phenotypes. These results demonstrate for the first time that YggS controls Ile and Val metabolism by modulating 2-ketobutyrate and CoA availability. Its function depends on PLP, and it is highly conserved in a wide range species, from bacteria to humans.