Structural model of human glucokinase in complex with glucose and ATP - Implications for the mutants that cause hypo- and hyperglycemia

Mutations In human glucokinase are implicated in the development of diabete s and hypoglycemia. Human glucokinase shares 54% identical amino acid resid ues with human brain hexokinase I. This similarity was used to model the st ructure of glucokinase by analogy to the crystal structure of brain hexokin ase. Glucokinase was modeled with both its substrates, glucose and MgATP, t o understand the effect of mutations. The glucose is predicted to form hydr ogen bond interactions with the side chains of glucokinase residues Thr 168 , Lys 169, Asn 204, Asp 205, Asn 231, and Glu 290, similar to those observe d for brain hexokinase I. The magnesium ion is coordinated by the carboxyla tes of Asp 78 and Asp 205 and the gamma-phosphate of ATP. ATP is predicted to form hydrogen bond interactions with residues Gly 81, Thr 82, Asn 83, Ar g 85, Lys 169, Thr 228, Lys 296, Thr 332, and Ser 336. Mutations of residue s close to the predicted ATP binding site produced dramatic changes in the K-m for ATP, the catalytic rate, and a loss of cooperativity, which confirm ed our model. Mutations of residues in the glucose binding site dramaticall y reduced the catalytic activity, as did a mutation that was predicted to d isrupt an alpha-helix. Other mutations located far from the active site gav e smaller changes in kinetic parameters. In the absence of a crystal struct ure for glucokinase, our models help rationalize the potential effects of m utations in diabetes and hypoglycemia, and the models may also facilitate t he discovery of pharmacological glucokinase activators and inhibitors.