The mechanism of regulation of hexokinase: new insights from the crystal structure of recombinant human brain hexokinase complexed with glucose and glucose-6-phosphate.
BACKGROUND
Hexokinase I is the pacemaker of glycolysis in brain tissue. The type I isozyme exhibits unique regulatory properties in that physiological levels of phosphate relieve potent inhibition by the product, glucose-6-phosphate (Gluc-6-P). The 100 kDa polypeptide chain of hexokinase I consists of a C-terminal (catalytic) domain and an N-terminal (regulatory) domain. Structures of ligated hexokinase I should provide a basis for understanding mechanisms of catalysis and regulation at an atomic level.


RESULTS
The complex of human hexokinase I with glucose and Gluc-6-P (determined to 2.8 A resolution) is a dimer with twofold molecular symmetry. The N- and C-terminal domains of one monomer interact with the C- and N-terminal domains, respectively, of the symmetry-related monomer. The two domains of a monomer are connected by a single alpha helix and each have the fold of yeast hexokinase. Salt links between a possible cation-binding loop of the N-terminal domain and a loop of the C-terminal domain may be important to regulation. Each domain binds single glucose and Gluc-6-P molecules in proximity to each other. The 6-phosphoryl group of bound Gluc-6-P at the C-terminal domain occupies the putative binding site for ATP, whereas the 6-phosphoryl group at the N-terminal domain may overlap the binding site for phosphate.


CONCLUSIONS
The binding synergism of glucose and Gluc-6-P probably arises out of the mutual stabilization of a common (glucose-bound) conformation of hexokinase I. Conformational changes in the N-terminal domain in response to glucose, phosphate, and/or Gluc-6-P may influence the binding of ATP to the C-terminal domain.
Aleshin
A E
AE
Department of Biochemistry and Biophysics, Iowa State University, Ames 50011, USA.
Zeng
C
C
Bourenkov
G P
GP
Bartunik
H D
HD
Fromm
H J
HJ
Honzatko
R B
RB
D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D001665:Binding Sites; D001921:Brain / Q000201:enzymology*; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005656:Fungal Proteins / Q000737:chemistry; D005947:Glucose / Q000737:chemistry*; D019298:Glucose-6-Phosphate / Q000737:chemistry*; D005991:Glycerol Kinase / Q000737:chemistry; D006593:Hexokinase / Q000737:chemistry*; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D016415:Sequence Alignment
D004791:Enzyme Inhibitors; D005656:Fungal Proteins; D011994:Recombinant Proteins; D019298:Glucose-6-Phosphate; D000255:Adenosine Triphosphate; D006593:Hexokinase; D005991:Glycerol Kinase; D005947:Glucose