Investigation of glucose binding sites on insulin

Possible insulin binding sites for D-glucose have been investigated theor. by docking and mol. dynamics (MD) simulations.  Two different docking programs for small mols. were used; Multiple Copy Simultaneous Search (MCSS) and Solvation Energy for Exhaustive Docking (SEED) programs.  The configurations resulting from the MCSS search were evaluated with a scoring function developed to est. the binding free energy.  SEED calcns. were performed using various values for the dielec. const. of the solute.  It is found that scores emphasizing non-polar interactions gave a preferential binding site in agreement with that inferred from recent fluorescence and NMR NOESY expts.  The calcd. binding affinity of -1.4 to -3.5 kcal/mol is within the measured range of -2.0±0.5 kcal/mol.  The validity of the binding site is suggested by the dynamical stability of the bound glucose when examd. with MD simulations with explicit solvent.  Alternative binding sites were found in the simulations and their relative stabilities were estd.  The motions of the bound glucose during mol. dynamics simulations are correlated with the motions of the insulin side chains that are in contact with it and with larger scale insulin motions.  These results raise the question of whether glucose binding to insulin could play a role in its activity.  The results establish the complementarity of mol. dynamics simulations and normal mode analyses with the search for binding sites proposed with small mol. docking programs.