Facial Selectivity between Carbohydrates and Aromatic Amino Acids Explained by a Combination of NCI, NBO and EDA Techniques with NMR Spectroscopy

The influence of electrostatic and dispersion components of intermolecular interactions on the recognition of carbohydrates by aromatic protein residues is important for many biological processes. Interactions between glucose and galactose and aromatic moieties of tryptophan, phenylalanine and histidine were investigated through H-1 nuclear magnetic resonance (NMR) chemical shift perturbation and fully explained by molecular modelling at the density functional theory (DFT) level. According to NMR experiments, aromatic amino acids interact preferably with one face of the carbohydrate and the calculations showed how intermolecular interactions were determinant in explaining the selectivity. Non-covalent interaction surfaces revealed that a CH bond oriented toward the center of the aromatic ring maximized the attractive interaction while minimizing the steric repulsion. Energy decomposition analyses showed that the dispersion component was stronger than the electrostatic component and contributes more when hydrogen bonds are not present in the studied complexes. However, it was the electrostatic component that correlated with the facial preference, especially for the complexes with tryptophan.