The effect of water on the binding of glycosaminoglycan saccharides to hydroxyapatite surfaces: a molecular dynamics study.

Sergio E Ruiz Hernandez,Nora H De Leeuw,Ian Streeter

doi:10.1039/c5cp02630j

Abstract

Classical molecular dynamics (MD) simulations have been employed to study the interaction of the saccharides glucuronic acid (GlcA) and N-acetylgalactosamine (GalNAc) with the (0001) and (011̄0) surfaces of the mineral hydroxyapatite (HAP). GlcA and GalNAc are the two constituent monosaccharides of the glycosaminoglycan chondroitin sulfate, which is commonly found in bone and cartilage and has been implicated in the modulation of the hydroxyapatite biomineralization process. MD simulations of the mineral surfaces and the saccharides in the presence of solvent water allowed the calculation of the adsorption energies of the saccharides on the HAP surfaces. The calculations show that GalNAc interacts with HAP principally through the sulfate and the carbonyl of acetyl amine groups, whereas the GlcA interacts primarily through the carboxylate functional groups. The mode and strength of the interaction depends on the orientation of the saccharide with respect to the surface and the level of disruption of the layer of water competing with the saccharide for adsorption sites on the HAP surface, suggesting that chondroitin 4-sulfate binds to the layer of solvent water rather than to HAP.

Highlights

Mineralised tissues such as bone and tooth enamel have a complex composite micro-architecture, in which an underlying matrix of fibrous organic material becomes strengthened by the deposition of inorganic apatite crystals
Where Esurf,solv is the average configurational energy of the hydrated surface, Esurf is the energy of the dry surface, EH2O is the energy of one liquid water molecule and n is the number of solvent water molecules
We have performed a series of molecular dynamics simulations to investigate the adsorption of two monosaccharides of a common glycosaminoglycan at three major surfaces of hydroxyapatite in aqueous environment

Summary

Introduction

Mineralised tissues such as bone and tooth enamel have a complex composite micro-architecture, in which an underlying matrix of fibrous organic material becomes strengthened by the deposition of inorganic apatite crystals. Glycosaminoglycans (GAGs) are polysaccharide molecules that are abundant in mineralised tissues, and are known to interact strongly with apatite crystals.[3,4,5] A GAG molecule is an unbranched polymer chain of two different types of monosaccharides linked together in alternation.[6] The most prevalent GAG found in mineralised tissues is chondroitin sulfate, shown, in which the alternating monosaccharides are glucuronic acid (GlcA) and N-acetylgalactosamine (GalNAc) shown in Fig. 1(b) and (c) respectively. This GAG can be sulfated to some a Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK

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Conclusion