ATOMIC INTERACTIONS BETWEEN PROTEINS AND CARBOHYDRATES. F. A. Quiocho^* N. K. Vyas^*, M. N. Vyas^* J. C. Spurlino^*, L. E. Rodseth^* and D. R. Bundle^{[[daggerdbl]]}, ^*Howard Hughes Medical Institute and Department of Biochemistry, Baylor College of Medicine Houston, Texas 77030, USA and ^{[[daggerdbl]]}Department of Chemistry, University of Alberta, Edmonton, Alberta TGG 2C6, Canada

Major features of the atomic interactions between proteins and carbohydrates that will be presented are based on the following refined structures: i) L-arabinose-binding protein (ABP) complexed with L-arabinose, D-galactose, D-fucose, and 4 deoxy and halide derivatives of D-galactose; ii) D-glucose/D-galactose-binding protein (GGBP) complexed with D-glucose and D-galactose; iii) maltodextrin-binding protein (MBP) complexed with maltose, maltotriose, maltotetraose and ß-cyclodextrin; and iv) antibody against the lipolysaccharides O-antigen of Shigella flexneri in the absence and presence of trisaccharide and pentasaccharide O-antigen segments. The first three proteins serve as initial receptors for bacterial active transport and chemotaxis. All proteins that bind carbohydrates can be distinguished into two groups or types depending primarily on the location of the binding site. Whereas the sites in proteins belonging to Group I (e.g., ABP, GGBP, lacI family of repressors) are buried and able to sequester the ligands, those of group II (e.g, immunoglobulins, lectins, etc.) are near the protein surface. Each group further possesses somewhat unique features. MBP has a binding site groove which exhibits properties of the two groups. Features of protein-carbohydrate interactions that will be discussed include i) hydrogen-bonding interactions, ii) van der Waals interactions, especially those arising from stacking interactions with aromatic residues, iii) role of water molecule, iv) structural plasticity, v) bound oligosaccharide conformations, vi) specificity, and vii) affinity.