Tyrosine-kinase Wzc from Escherichia coli possesses an ATPase activity regulated by autophosphorylation

The catalytic mechanism of bacterial tyrosine-kinases (PTK) is poorly understood. These enzymes possess Walker A and B ATP-binding motifs, which are effectively required for their autophosphorylation whereas these motifs are usually found in ATP-binding proteins but not in eukaryotic protein-kinases. It was previously shown that the PTK Wzc in Escherichia coli undergoes intra- and interphosphorylation. In this work, it is shown that, in addition to its kinase activity, Wzc produces free inorganic phosphate. It is demonstrated that this ATPase activity is increased significantly by intraphosphorylation of Wzc. The fact that intraphosphorylation of Wzc does not affect Wzc affinity for ATP was also demonstrated and it was suggested that it could rather modify the local environment of the ATP molecule in the catalytic site so as to render Wzc more liable to catalyze ATP hydrolysis and interphosphorylation. These results should contribute to better understanding of the catalytic mechanism of this particular class of tyrosine-kinases, which seems, so far, restricted to bacteria.