Structure of the Enterococcal Glycerol Kinase: Regulation of Enzymatic Activity Via Direct Phosphorylation. Joanne I. Yeh1, Al Claiborne3, Josef Deutscher4, and Wim G.J. Hol1, 1Department of Biological Structure, 2Howard Hughes Medical Institute, University of Washington, 3Department of Biochemistry, Wake Forest University, 4Institute de Biologie et Chimie des Proteines, CNRS
The x-ray crystal structure of the glycerol kinase has been determined by a combination of MIR and molecular replacement techniques. This kinase, isolated from the Gram-positive Enterococcus casseliflavus bacterium, is significantly different from the Gram-negative kinase, in the quaternary structural organization and in its mechanism of regulation. In the Gram-positive systems, glycerol kinase is regulated via phosphorylation on a histidyl residue by the protein HPr (Deutscher and Sauerwald, 1986). This is in contrast to Gram-negative systems where the kinase is regulated by allosteric interaction with Enzyme IIAGlc (de Boer et al, 1986). Enzyme IIAGlc appears to have no regulatory role on the activity of the glycerol kinase in the enterococcus system.
The structures of the enterococcal glycerol kinase provide interesting insight to how the kinase is activated by phosphorylation. The phosphorylation site is distally located from the glycerol-binding site and the structures of the native and mutants of the kinase suggests the structural changes that may result in activation of the enzyme. In addition to the native structure of the kinase, the structure of a mutant where the phosphorylated histidyl residue has been changed so that its activity is no longer stimulated by phosphorylation, has also been determined. Interestingly, the mutant contains some significant structural changes from the native. Comparison of the structures of the Enterococcus casseliflavus and Escherichia coli glycerol kinases and the results of these structural studies are likely to be generally applicable to the respective Gram-positive and Gram-negative systems.
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