Ophthalmic acid accumulation in an Escherichia coli mutant lacking the conserved pyridoxal 5 '-phosphate-binding protein YggS

摘要

Escherichia coli YggS is a highly conserved pyridoxal 5'-phosphate (PLP)-binding protein whose biochemical function is currently unknown. A previous study with a yggS-deficient E. coli strain (Delta yggS) demonstrated that YggS controls L-Ile- and L-Val-metabolism by modulating 2-ketobutyrate (2-KB), L-2-aminobutyrate (L-2-AB), and/or coenzyme A (CoA) availability in a PLP-dependent fashion. In this study, we found that Delta yggS accumulates an unknown metabolite as judged by amino acid analyses. LC/MS and MS/MS analyses of the compound with propyl chloroformate derivatization, and co-chromatography analysis identified this compound as gamma-L-glutamyl-L-2-aminobutyryl-glycine (ophthalmic acid), a glutathione (GSH) analogue in which the L-Cys moiety is replaced by L-2-AB. We also determine the metabolic consequence of the yggS mutation. Absence of YggS initially increases L-2-AB availability, and then causes ophthalmic acid accumulation and CoA limitation in the cell. The expression of a gamma-glutamylcysteine synthetase and a glutathione synthetase in a Delta yggS background causes high-level accumulation of ophthalmic acid in the cells (similar to 1.2 nmol/mg cells) in a minimal synthetic medium. This opens the possibility of a first fermentative production of ophthalmic acid. (C) 2016, The Society for Biotechnology, Japan. All rights reserved.