title: Crystal structures of mutant monomeric hexokinase I reveal multiple ADP binding sites and conformational changes relevant to allosteric regulation.
abstract: Hexokinase I, the pacemaker of glycolysis in brain tissue, is composed of two structurally similar halves connected by an alpha-helix. The enzyme dimerizes at elevated protein concentrations in solution and in crystal structures; however, almost all published data reflect the properties of a hexokinase I monomer in solution. Crystal structures of mutant forms of recombinant human hexokinase I, presented here, reveal the enzyme monomer for the first time. The mutant hexokinases bind both glucose 6-phosphate and glucose with high affinity to their N and C-terminal halves, and ADP, also with high affinity, to a site near the N terminus of the polypeptide chain. Exposure of the monomer crystals to ADP in the complete absence of glucose 6-phosphate reveals a second binding site for adenine nucleotides at the putative active site (C-half), with conformational changes extending 15 A to the contact interface between the N and C-halves. The structures reveal distinct conformational states for the C-half and a rigid-body rotation of the N-half, as possible elements of a structure-based mechanism for allosteric regulation of catalysis.
authors.affiliation: Department of Biochemistry Biophysics and Molecular Biology, Iowa State University, Ames, IA 50011, USA.
authors.forename: A E
authors.initials: AE
authors.lastname: Aleshin
authors.forename: C
authors.initials: C
authors.lastname: Kirby
authors.forename: X
authors.initials: X
authors.lastname: Liu
authors.forename: G P
authors.initials: GP
authors.lastname: Bourenkov
authors.forename: H D
authors.initials: HD
authors.lastname: Bartunik
authors.forename: H J
authors.initials: HJ
authors.lastname: Fromm
authors.forename: R B
authors.initials: RB
authors.lastname: Honzatko
mesh_terms: D000244:Adenosine Diphosphate / Q000737:chemistry / Q000378:metabolism*; D000494:Allosteric Regulation; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000201:enzymology; D019298:Glucose-6-Phosphate / Q000737:chemistry / Q000378:metabolism; D006593:Hexokinase / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D011487:Protein Conformation
chemical_list: D019298:Glucose-6-Phosphate; D000244:Adenosine Diphosphate; D006593:Hexokinase