Search for novel targets of the PII signal transduction protein in Bacteria identifies the BCCP component of acetyl‐CoA carboxylase as a PII binding partner

The P_II family comprises a group of widely distributed signal transduction proteins. The archetypal function of P_II is to regulate nitrogen metabolism in bacteria. As P_II can sense a range of metabolic signals, it has been suggested that the number of metabolic pathways regulated by P_II may be much greater than described in the literature. In order to provide experimental evidence for this hypothesis a P_II protein affinity column was used to identify P_II targets in Azospirillum brasilense. One of the P_II partners identified was the biotin carboxyl carrier protein (BCCP), a component of the acetyl‐CoA carboxylase which catalyses the committed step in fatty acid biosynthesis. As BCCP had been previously identified as a P_II target in Arabidopsis thaliana we hypothesized that the P_II–BCCP interaction would be conserved throughout Bacteria. In vitro experiments using purified proteins confirmed that the P_II–BCCP interaction is conserved in Escherichia coli. The BCCP–P_II interaction required MgATP and was dissociated by increasing 2‐oxoglutarate. The interaction was modestly affected by the post‐translational uridylylation status of P_II; however, it was completely dependent on the post‐translational biotinylation of BCCP.