Purification and in vitro phosphorylation of Myxococcus xanthus AsgA protein

The deduced amino acid sequence of the Myxococcus xanthus AsgA protein contains an N-terminal domain that is homologous to the receiver of response regulators and a C-terminal domain that is homologous to the transmitter of histidine protein kinases. We overexpressed affinity-tagged AsgA in Escherichia coli, purified the recombinant protein, and showed that AsgA has autokinase activity in vitro. The results of chemical-stability assays suggest that AsgA is phosphorylated on a histidine and provide no evidence for transfer of the phosphoryl group to the conserved aspartate of the receiver domain.