Sugar recognition by a glucose/galactose receptor. Evaluation of binding energetics from molecular dynamics simulations.

A new theoretical method for free energy calculations is used to compute the absolute binding constants for beta-D-glucose and methyl-beta-D-galactoside to the periplasmic glucose/galactose receptor from Salmonella typhimurium. The computer simulation results agree well with available experimental data and make it possible to assess the sources of both the high affinity as well as the specificity for glucose. It was found that the major contribution to the binding energy comes from electrostatic interactions and particularly hydrogen bonds of the charge-dipole type. We also predict the structure of the complex with methyl-galactoside as this has not yet been experimentally determined.