A DENSITY-FUNCTIONAL THEORY INVESTIGATION OF METAL-ION BINDING-SITES IN MONOSACCHARIDES

The density functional theory method is used to study metal ion bindin g to simple carbohydrates such as cis-inositol and beta-D-glucose. The complexes formed between Be2+, Mg2+, Ca2+, and Li+ and cis-inositol a nd the complexes formed between Ca2+ and beta-D-glucose are optimized and metal binding sites are identified. There are two metal binding si tes in cis-inositol and five in beta-D-glucose. Our calculations demon strate that smaller ions such as Be2+ prefer to bind in the ax-ax-ax s ite of cis-inositol, while larger ions such Mg2+ and Li+ favor the ax- eq-ax site of cis-inositol. The preferred metal binding site in Ca2+-c is-inositol is defined by four hydroxyl groups instead of three (one e quatorial and three axial OH). Among the five metal binding sites in b eta-D-glucose, the one defined by the ring oxygen atom, C1-OH and C6-O H is the most preferred site where Ca2+ binds to three oxygen atoms. T his tendency of metal ions to maximize interactions with carbohydrate ligands in the gas phase is in agreement with previous experimental an d theoretical studies. The relevance of these metal-carbohydrate inter actions in cell surface carbohydrate-binding proteins is also discusse d. This study has demonstrated that the density functional theory meth od is a good method for identifying metal ion binding sites in carbohy drates.