YddG from Escherichia coli promotes export of aromatic amino acids

The inner membrane protein YddG of Escherichia coli is a homologue of the known amino acid exporters RhtA and YdeD. It was found that the yddG gene overexpression conferred resistance upon E. coli cells to the inhibiting concentrations of L-phenylalanine and aromatic amino acid analogues, DL-p-fluorophenylalanine, DL-o-fluorophenylalanine and DL-5-fluorotryptophan. In addition, yddG overexpression enhanced the production of L-phenylalanine, L-tyrosine or L-tryptophan by the respective E. coli-producing strains. On the other hand, the inactivation of yddG decreased the aromatic amino acid accumulation by these strains. The cells of the E. coli L-phenylalanine-producing strain containing overexpressed yddG accumulated less L-phenylalanine inside and exported the amino acid at a higher rate than the cells of the isogenic strain containing wild-type yddG. Taken together, these results indicate that YddG functions as an aromatic amino acid exporter.