Binding of glycosaminoglycan saccharides to hydroxyapatite surfaces: A density functional theory study

Density functional theory calculations implemented by the SIESTA code are used to study the interactions of the saccharides N-acetylgalactosamine (GalNAc) and glucuronic acid (GlcA) with the (0001) and [Formula: see text] surfaces of the mineral hydroxyapatite (HAP). GalNAc and GlcA are the constituent monosaccharides of chondroitin, which is a glycosaminoglycan found in bone and cartilage, and whose interactions with HAP have been implicated as a controlling factor in the process of biomineralisation. Geometry optimisation calculations are used to identify low energy adsorption structures of the monosaccharides on the HAP surfaces, and to calculate the corresponding adsorption energies. The calculations show that GalNAc interacts with HAP principally through its hydroxy and acetyl amine functional groups, and deprotonated GlcA interacts principally through its hydroxy and carboxylate functional groups. The mode and strength of adsorption depends on the orientation of the saccharide with respect to the HAP surface, which has implications for the structural conformation of chondroitin chains in the presence of hydroxyapatite. Both monosaccharides bind more strongly to the [Formula: see text] surface than to the (0001) surface.