A novel mode of control of Mycoplasma pneumoniae HPr kinase/phosphatase activity reflects its parasitic lifestyle.

Among the few regulatory proteins encoded by Mycoplasma pneumoniae is HPr kinase/phosphatase (HPrK/P), the key regulator of carbon metabolism in low-GC Gram-positive bacteria. The corresponding gene, hprK, and the gene encoding the target protein HPr, ptsH, were overexpressed. In vitro analysis of the purified proteins confirmed ATP-dependent phosphorylation of HPr by HPrK/P. In contrast to HPrK/P of Bacillus subtilis, which is by default a phosphatase and needs high ATP concentrations for kinase activity, the M. pneumoniae enzyme exhibits kinase activity at very low ATP concentrations and depends on P(i) for phosphatase activity. This inverted control of enzymic activity may result from the adaptation to very different ecological niches. While the standard activities of HPrK/P from M. pneumoniae and other Gram-positive bacteria differ, they are both modulated by the concentration of ATP, P(i) and glycolytic intermediates. Site-directed mutagenesis of a potential ATP-binding site and of the HPrK/P signature sequence resulted in four different activity classes: (i) inactive proteins, (ii) enzymes with reduced kinase and phosphatase activities, (iii) enzymes that had lost phosphatase, but not kinase activity, and (iv) enzymes that exhibited increased phosphatase activity.