Structure of the Regulatory Complex of Escherichia coli III Glc with Glycerol Kinase

The phosphocarrier protein III Glc is an integral component of the bacterial phosphotransferase (PTS) system. Unphosphorylated III Glc inhibits non-PTS carbohydrate transport systems by binding to diverse target proteins. The crystal structure at 2.6 Å resolution of one of the targets, glycerol kinase (GK), in complex with unphosphorylated III Glc , glycerol, and adenosine diphosphate was determined. GK contains a region that is topologically identical to the adenosine triphosphate binding domains of hexokinase, the 70-kD heat shock cognate, and actin. III Glc binds far from the catalytic site of GK, indicating that long-range conformational changes mediate the inhibition of GK by III Glc . GK and III Glc are bound by hydrophobic and electrostatic interactions, with only one hydrogen bond involving an uncharged group. The phosphorylation site of III Glc , His 90 , is buried in a hydrophobic environment formed by the active site region of III Glc and a 3 10 helix of GK, suggesting that phosphorylation prevents III Glc binding to GK by directly disrupting protein-protein interactions.