Domain Bridging Interactions in the Allosteric Network for IIAGlc Inhibition of the Escherichia coli Glycerol Kinase
Previous studies on inhibition of the Escherichia coli glycerol kinase enzyme have suggested that subunit-subunit or domain bridging interactions form part of the network in communicating ligand binding to inhibition. In this study, five amino acids were identified to be in close proximity to an Arg369 residue which is a domain bridging residue. Three of the amino acid residues (Q37, Y39 and Q104) are in domain I of the enzyme subunit, while the other two (M308 and Q314) are in domain II of the enzyme subunit. To evaluate the importance of each domain bridging residue in IIAGlc inhibition, alanine substitutions were made of the residues, and the kinetic properties characterized with respect to IIAGlc inhibition. Kinetic parameters obtained for each variant glycerol kinase enzyme was compared to values obtained for the Wild Type enzyme to assess the importance of the amino acid residue in IIAGlc inhibition. The effects of the substitutions on FBP inhibition as well as catalysis of the enzyme were also analyzed by obtaining kinetic parameters for each of the variant enzymes. The results from this study indicate that the domain I bridging interactions with Arg369 are important in IIAGlc regulation of the E. coli glycerol kinase enzyme. The domain II bridging interactions appear to be unimportant in regulating IIAGlc inhibition. Two of the domain I bridging residues studied were also found to be important in FBP inhibition. These results indicate that some the domain bridging residues seen to be involved in IIAGlc regulation also appear to be involved in FBP regulation. In catalysis, with the exception of Q314, the rest of the domain I and II bridging residues appear to be important for substrate binding and/or catalysis.