HK Utrecht: missense mutation in the active site of human hexokinase associated with hexokinase deficiency and severe nonspherocytic hemolytic anemia.
van Wijk R., Rijksen G., Huizinga E.G., Nieuwenhuis H.K., van Solinge W.W.
Hexokinase deficiency is a rare autosomal recessive disease with a clinical phenotype of severe hemolysis. We report a novel homozygous missense mutation in exon 15 (c.2039C>G, HK [hexokinase] Utrecht) of HK1, the gene that encodes red blood cell-specific hexokinase-R, in a patient previously diagnosed with hexokinase deficiency. The Thr680Ser substitution predicted by this mutation affects a highly conserved residue in the enzyme's active site that interacts with phosphate moieties of adenosine diphosphate, adenosine triphosphate (ATP), and inhibitor glucose-6-phosphate. We correlated the molecular data to the severe clinical phenotype of the patient by means of altered enzymatic properties of partially purified hexokinase from the patient, notably with respect to Mg(2+)-ATP binding. These kinetic properties contradict those obtained from a recombinant mutant brain hexokinase-I with the same Thr680Ser substitution. This contradiction thereby stresses the valuable contribution of studying patients with hexokinase deficiency to achieve a better understanding of hexokinase's key role in glycolysis.