REGULATION OF HEXOKINASE-I - CRYSTAL-STRUCTURE OF RECOMBINANT HUMAN BRAIN HEXOKINASE COMPLEXED WITH GLUCOSE AND PHOSPHATE

Hexokinase I, the pacemaker of glycolysis in brain tissue and red bloo d cells, is comprised of two similar domains fused into a single polyp eptide chain. The C-terminal half of hexokinase I is catalytically act ive, whereas the N-terminal half is necessary for the relief of produc t inhibition by phosphate. A crystalline complex of recombinant human hexokinase I with glucose and phosphate (2.8 Angstrom resolution) reve als a single binding site for phosphate and glucose at the N-terminal half of the enzyme. Glucose and phosphate stabilize the N-terminal hal f in a closed conformation. Unexpectedly, glucose binds weakly to the C-terminal half of the enzyme and does not by itself stabilize a close d conformation. Evidently a stable, closed C-terminal half requires ei ther ATP or glucose 6-phosphate along with glucose. The crystal struct ure here, in conjunction with other studies in crystallography and dir ected mutation, puts the phosphate regulatory site at the N-terminal h alf, the site of potent product inhibition at the C-terminal half, and a secondary site for the weak interaction of glucose 6-phosphate at t he N-terminal half of the enzyme. The relevance of crystal structures of hexokinase I to the properties of monomeric hexokinase I and oligom ers of hexokinase I bound to the surface of mitochondria is discussed. (C) 1998 Academic Press.