Oligosaccharides Display Both Rigidity and High Flexibility in Water as Determined by 13C NMR Relaxation and 1H,1H NOE Spectroscopy: Evidence of anti-ϕ and anti-ψ Torsions in the Same Glycosidic Linkage
✍ Scribed by Christer Höög; Clas Landersjö; Göran Widmalm
- Publisher
- John Wiley and Sons
- Year
- 2001
- Tongue
- English
- Weight
- 177 KB
- Volume
- 7
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
The trisaccharide b-d-Glcp-(1 3 2)-b-d-Glcp-(1 3 3)-a-d-Glcp-OMe has been investigated by molecular dynamics (MD) simulations and NMR experiments in water. 13 C spinlattice (T 1 ) and spin ± spin (T 2 ) relaxation times, together with 1 H, 13 C NOE data were measured at two magnetic field strengths (9.4 and 14.1 T) in a 277 K D 2 O solution. Relaxation data interpreted by means of the model-free formalism revealed a rigid (S 2 $ 0.9) oligosaccharide tumbling in solution.
1 H, 1 H Cross-relaxation rates were determined at 600 MHz by 1D DPFGSE NOESY and T-ROESY experiments, which provided high quality data and subsequently proton ± proton distances within the trisaccharide. The presence of anti conformers at both torsions of a glycosidic linkage is demonstrated for the first time. MD simulations were carried out to facilitate analysis of the NOE data. In total, 15 simulationsÐ starting from five different conformational statesÐwere performed, with production runs of up to 10 ns, resulting in 83 ns of oligosaccharide dynamics in water. anti Conformers were populated to different degrees in the simulations, especially at the f 2 torsion angle. By combining the results from the NOE experiments and the MD simulations, the anti conformers at the (1 3 2)-linkage were quantified as 7 % anti-f 2 and 2 % anti-y 2 , revealing a highly flexible trisaccharide in which large conformational changes occur. From the MD simulations, interresidue hydrogen bonding, from HO2'' to O2 or O3, was significantly populated ($ 40 %) in both of the anti conformational states. The contentious issue over rigidity versus flexibility in oligosaccharides has thus been thoroughly examined, showing that the dynamics should be taken into account for a relevant description of the molecular system.