Eklund Robert, Lycknert Kristina, Söderman Peter, Widmalm Göran
Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, S-10691 Stockholm, Sweden.
J Phys Chem B. 2005 Oct 27;109(42):19936-45. doi: 10.1021/jp053198o.
The conformational preference of alpha-l-Rhap-(1-->2)[alpha-l-Rhap-(1-->3)]-alpha-l-Rhap-OMe in solution has been studied by NMR spectroscopy using one-dimensional (1)H,(1)H T-ROESY experiments and measurement of trans-glycosidic (3)J(C,H) coupling constants. Molecular dynamics (MD) simulations with a CHARMM22 type of force field modified for carbohydrates were performed with water as the explicit solvent. The homonuclear cross-relaxation rates, interpreted as effective proton-proton distances, were compared to those obtained from simulation. Via a Karplus torsional relationship, (3)J(C,H) values were calculated from simulation and compared to experimental data. Good agreement was observed between experimental data and the MD simulation, except for one inter-residue T-ROE between protons in the terminal sugar residues. The results show that the trisaccharide exhibits substantial conformational flexibility, in particular along the psi glycosidic torsion angles. Notably, for these torsions, a high degree of correlation (77%) was observed in the MD simulation revealing either psi(2)(+) psi(3)(+) or psi(2)(-)psi(3)(-) states. The simulations also showed that non-exoanomeric conformations were present at the phi torsion angles, but to a limited extent, with the phi(3) state populated to a larger extent than the phi(2) state. Further NMR analysis of the trisaccharide by translational diffusion measurements and (13)C T(1) relaxation experiments quantified global reorientation using an anisotropic model together with interpretation of the internal dynamics via the "model-free" approach. Fitting of the dynamically averaged states to experimental data showed that the psi(2)(+)psi(3)(+) state is present to approximately 49%, psi(2)(-) psi(3)(-) to approximately 39%, and phi(3) (non-exo) to approximately 12%. Finally, using a dynamic and population-averaged model, (1)H,(1)H T-ROE buildup curves were calculated using a full relaxation matrix approach and were found to be in excellent agreement with experimental data, in particular for the above inter-residue proton-proton interaction between the terminal residues.
通过核磁共振光谱法，利用一维氢氢T-ROESY实验和反式糖苷键碳氢耦合常数（³J(C,H)）的测量，研究了α-L-鼠李糖基-(1→2)[α-L-鼠李糖基-(1→3)]-α-L-鼠李糖甲酯在溶液中的构象偏好。采用为碳水化合物修改的CHARMM22型力场进行分子动力学（MD）模拟，以水作为显式溶剂。将解释为有效质子-质子距离的同核交叉弛豫率与模拟得到的结果进行比较。通过Karplus扭转关系，从模拟中计算³J(C,H)值并与实验数据进行比较。实验数据与MD模拟之间观察到良好的一致性，但末端糖残基中质子之间的一个残基间T-ROE除外。结果表明，三糖表现出显著的构象灵活性，特别是沿着ψ糖苷扭转角。值得注意的是，对于这些扭转，在MD模拟中观察到高度相关性（77%），揭示了ψ₂⁺ψ₃⁺或ψ₂⁻ψ₃⁻状态。模拟还表明，在φ扭转角处存在非异头构象，但程度有限，φ₃状态的占据程度大于φ₂状态。通过平移扩散测量和¹³C T₁弛豫实验对三糖进行进一步的核磁共振分析，使用各向异性模型量化整体重排，并通过“无模型”方法解释内部动力学。将动态平均状态拟合到实验数据表明，ψ₂⁺ψ₃⁺状态约占49%，ψ₂⁻ψ₃⁻状态约占39%，φ₃（非异头）状态约占12%。最后，使用动态和种群平均模型，采用完整弛豫矩阵方法计算氢氢T-ROE积累曲线，发现与实验数据非常吻合，特别是对于末端残基之间上述残基间质子-质子相互作用。
