Activation of Bacillus subtilis Ugd by the BY-kinase PtkA proceeds via phosphorylation of its residue tyrosine 70.

The phosphorylation-dependent activation of bacterial UDP-glucose dehydrogenases by BY-kinases has been previously described in several bacterial model organisms, but the identity of phosphorylated tyrosine(s) and the exact activation mechanism remained unknown. A recent site-specific phosphoproteomic study indicated that tyrosine 70 is phosphorylated in the Bacillus subtilis UDP-glucose dehydrogenase Ugd. In this study we confirm that this tyrosine 70 is indeed the main residue phosphorylated by the cognate BY-kinase PtkA. Homology-based modeling of the Ugd structure using structures from UDP-glucose/GDP-mannose dehydrogenases revealed that this residue is in close proximity to the NAD-binding site. We identified lysine 108 as the second important residue involved in Ugd activation. Enzymatic characterization of the Ugd proteins mutated in residues tyrosine 70 or lysine 108 suggested a phosphorylation-based regulatory mechanism. This study represents the first attempt to understand the activation of a bacterial enzyme by tyrosine phosphorylation at the molecular level.