The protein-protein interaction network of the Escherichia coli EIIANtr regulatory protein reveals a role in cell motility and metabolic control.

The nitrogen-related PTSNtr system, present in many Proteobacteria including Escherichia coli, acts as a phosphorelay cascade composed of the EINtr, NPr and EIIANtr proteins. Phosphotransfer initiates with phosphoenolpyruvate-dependent EINtr autophosphorylation, the phosphoryl group is then transferred to NPr and finally to a conserved histidine residue on EIIANtr. The reporter metabolites l-glutamine and 2-oxoglutarate reciprocally regulate EINtr autophosphorylation (Lee et al., 2013) and consequently the phosphorylation status of the PTSNtr components is controlled by the availability of nitrogen and carbon. The final phosphate acceptor, EIIANtr, regulates a range of cellular process by acting as the central hub of a complex protein-protein interaction network. Contact between EIIANtr and its target proteins is usually regulated by the EIIANtr phosphorylation status. In this study we performed ligand fishing assays coupled to label-free quantitative proteomics to examine the protein-protein interaction network of E. coli EIIANtr and a phosphomimic variant of the protein. The ligand fishing data, along with phenotypic analysis, indicated that EIIANtr interacts with proteins related to chemotaxis and thereby regulates cell motility. Important metabolic enzymes were also identified as potential EIIANtr binding partners.