Phosphorylation/dephosphorylation of the receiver module at the conserved aspartate residue controls transphosphorylation activity of histidine kinase in sensor protein ArcB of Escherichia coli.

A membrane sensor protein, ArcB, recognizes anaerobic environments and signals the information to the cognate regulator, ArcA. This in vitro study presents the process and control of the signal-transduction phosphorylation. In the presence of ATP, the ArcB transmitter module undergoes autophosphorylation and then transfers the phosphoryl group to its own receiver module as well as to the ArcA receiver module. Results suggest that the phosphoryl group of the ArcB receiver module is released by an intrinsic phosphatase activity. D-Lactate inhibits the phosphatase activity that removes phosphoaspartate groups from the receiver module in ArcB, and the associated increase in phosphorylation of this module leads to an activation of transphosphorylation of subsequently added phosphohistidine groups on ArcB to the receiver module of ArcA. A similar effect was also observed in the presence of pyruvate, acetate, or NADH. Conversely, the non-phosphorylated ArcB receiver module completely inhibits the intermolecular transphosphorylation. Thus, the phosphorylation state of the ArcB receiver module controls signal transduction from ArcB to ArcA. Since the intrinsic phosphatase activity is inhibited by cellular metabolites that increasingly accumulate by anaerobiosis, the enzyme portion of ArcB may be involved in sensing anaerobic environments through cellular metabolites in vivo.