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Catalytic activation of human glucokinase by substrate binding – residue contacts involved in the binding of D ‐glucose to the super‐open form and conformational transitions
Author(s) -
Molnes Janne,
Bjørkhaug Lise,
Søvik Oddmund,
Njølstad Pål R.,
Flatmark Torgeir
Publication year - 2008
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2008.06391.x
Subject(s) - glucokinase , conformational change , chemistry , stereochemistry , tryptophan , binding site , mutagenesis , residue (chemistry) , saturated mutagenesis , enzyme , active site , biochemistry , site directed mutagenesis , biophysics , crystallography , mutation , biology , mutant , amino acid , gene
α‐ d ‐Glucose activates glucokinase (EC 2.7.1.1) on its binding to the active site by inducing a global hysteretic conformational change. Using intrinsic tryptophan fluorescence as a probe on the α‐ d ‐glucose induced conformational changes in the pancreatic isoform 1 of human glucokinase, key residues involved in the process were identified by site‐directed mutagenesis. Single‐site W→F mutations enabled the assignment of the fluorescence enhancement (Δ F / F 0 ) mainly to W99 and W167 in flexible loop structures, but the biphasic time course of Δ F / F 0 is variably influenced by all tryptophan residues. The human glucokinase–α‐ d ‐glucose association ( K d = 4.8 ± 0.1 m m at 25 °C) is driven by a favourable entropy change (Δ S = 150 ± 10 J·mol −1 ·K −1 ). Although X‐ray crystallographic studies have revealed the α‐ d ‐glucose binding residues in the closed state, the contact residues that make essential contributions to its binding to the super‐open conformation remain unidentified. In the present study, we combined functional mutagenesis with structural dynamic analyses to identify residue contacts involved in the initial binding of α‐ d ‐glucose and conformational transitions. The mutations N204A, D205A or E256A/K in the L‐domain resulted in enzyme forms that did not bind α‐ d ‐glucose at 200 m m and were essentially catalytically inactive. Our data support a molecular dynamic model in which a concerted binding of α‐ d ‐glucose to N204, N231 and E256 in the super‐open conformation induces local torsional stresses at N204/D205 propagating towards a closed conformation, involving structural changes in the highly flexible interdomain connecting region II (R192‐N204), helix 5 (V181‐R191), helix 6 (D205‐Y215) and the C‐terminal helix 17 (R447‐K460).