Cross-Talk between the Canonical and the Nitrogen-Related Phosphotransferase Systems Modulates Synthesis of the KdpFABC Potassium Transporter in Escherichia coli

Abstract

Many Proteobacteria possess the regulatory nitrogen-related phosphotransferase system (PTS(Ntr)), which operates in parallel to the transport PTS. PTS(Ntr) is composed of the proteins EI(Ntr) and NPr and the final phosphate acceptor EIIA(Ntr). Both PTSs can exchange phosphoryl groups among each other. Proteins governing K(+) uptake represent a major target of PTS(Ntr) in Escherichia coli. Nonphosphorylated EIIA(Ntr) binds and stimulates the K(+) sensor KdpD, which activates expression of the kdpFABC operon encoding a K(+) transporter. Here we show that this regulation also operates in an ilvG(+) strain ruling out previous concern about interference with a nonfunctional ilvG allele present in many strains. Furthermore, we analyzed phosphorylation of EIIA(Ntr). In wild-type cells EIIA(Ntr) is predominantly phosphorylated, regardless of the growth stage and the utilized carbon source. However, cross-phosphorylation of EIIA(Ntr) by the transport PTS becomes apparent in the absence of EI(Ntr): EIIA(Ntr) is predominantly nonphosphorylated when cells grow on a PTS sugar and phosphorylated when a non-PTS carbohydrate is utilized. These differences in phosphorylation are transduced into corresponding kdpFABC transcription levels. Thus, the transport PTS may affect phosphorylation of EIIA(Ntr) and accordingly modulate processes controlled by EIIA(Ntr). Our data suggest that this cross-talk becomes most relevant under conditions that would inhibit activity of EI(Ntr).