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A 3D-structural model of unsulfated chondroitin from high-field NMR: 4-sulfation has little effect on backbone conformation.

ABSTRACT: The glycosaminoglycan chondroitin sulfate is essential in human health and disease but exactly how sulfation dictates its 3D-structure at the atomic level is unclear. To address this, we have purified homogenous oligosaccharides of unsulfated chondroitin (with and without (15)N-enrichment) and analysed them by high-field NMR to make a comparison published chondroitin sulfate and hyaluronan 3D-structures. The result is the first full assignment of the tetrasaccharide and an experimental 3D-model of the hexasaccharide (PDB code 2KQO). In common with hyaluronan, we confirm that the amide proton is not involved in strong, persistent inter-residue hydrogen bonds. However, in contrast to hyaluronan, a hydrogen bond is not inferred between the hexosamine OH-4 and the glucuronic acid O5 atoms across the beta(1-->3) glycosidic linkage. The unsulfated chondroitin bond geometry differs slightly from hyaluronan by rotation about the beta(1-->3) psi dihedral (as previously predicted by simulation), while the beta(1-->4) linkage is unaffected. Furthermore, comparison shows that this glycosidic linkage geometry is similar in chondroitin-4-sulfate. We therefore hypothesise that both hexosamine OH-4 and OH-6 atoms are solvent exposed in chondroitin, explaining why it is amenable to sulfation and hyaluronan is not, and also that 4-sulfation has little effect on backbone conformation. Our conclusions exemplify the value of the 3D-model presented here and progress our understanding of glycosaminoglycan molecular properties.

SUBMITTER: Sattelle BM

PROVIDER: S-EPMC3098369 | biostudies-literature | 2010 Jan

REPOSITORIES: biostudies-literature

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A 3D-structural model of unsulfated chondroitin from high-field NMR: 4-sulfation has little effect on backbone conformation.

Sattelle Benedict M BM Shakeri Javad J Roberts Ian S IS Almond Andrew A

Carbohydrate research 20091123 2

The glycosaminoglycan chondroitin sulfate is essential in human health and disease but exactly how sulfation dictates its 3D-structure at the atomic level is unclear. To address this, we have purified homogenous oligosaccharides of unsulfated chondroitin (with and without (15)N-enrichment) and analysed them by high-field NMR to make a comparison published chondroitin sulfate and hyaluronan 3D-structures. The result is the first full assignment of the tetrasaccharide and an experimental 3D-model ...[more]

PMID: 20022001

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Project description:Chondroitin sulfate (CS) is one of several glycosaminoglycans that are major components of proteoglycans. A linear polymer consisting of repeats of the disaccharide -4GlcA?1-3GalNAc?1-, CS undergoes differential sulfation resulting in five unique sulfation patterns. Because of the dimer repeat, the CS glycosidic "backbone" has two distinct sets of conformational degrees of freedom defined by pairs of dihedral angles: (?1, ?1) about the ?1-3 glycosidic linkage and (?2, ?2) about the ?1-4 glycosidic linkage. Differential sulfation and the possibility of cation binding, combined with the conformational flexibility and biological diversity of CS, complicate experimental efforts to understand CS three-dimensional structures at atomic resolution. Therefore, all-atom explicit-solvent molecular dynamics simulations with Adaptive Biasing Force sampling of the CS backbone were applied to obtain high-resolution, high-precision free energies of CS disaccharides as a function of all possible backbone geometries. All 10 disaccharides (?1-3 vs ?1-4 linkage × five different sulfation patterns) were studied; additionally, ion effects were investigated by considering each disaccharide in the presence of either neutralizing sodium or calcium cations. GlcA?1-3GalNAc disaccharides have a single, broad, thermodynamically important free-energy minimum, whereas GalNAc?1-4GlcA disaccharides have two such minima. Calcium cations but not sodium cations bind to the disaccharides, and binding is primarily to the GlcA -COO(-) moiety as opposed to sulfate groups. This binding alters the glycan backbone thermodynamics in instances where a calcium cation bound to -COO(-) can act to bridge and stabilize an interaction with an adjacent sulfate group, whereas, in the absence of this cation, the proximity of a sulfate group to -COO(-) results in two like charges being both desolvated and placed adjacent to each other and is found to be destabilizing. In addition to providing information on sulfation and cation effects, the present results can be applied to building models of CS polymers and as a point of comparison in studies of CS polymer backbone dynamics and thermodynamics.

Dataset Information

A 3D-structural model of unsulfated chondroitin from high-field NMR: 4-sulfation has little effect on backbone conformation.

Publications

A 3D-structural model of unsulfated chondroitin from high-field NMR: 4-sulfation has little effect on backbone conformation.

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