Department of Structural and Molecular Biology, Division of Biosciences, Darwin Building, University College London, Gower Street, London WC1E 6BT, United Kingdom.
J Biol Chem. 2011 Jul 15;286(28):24842-54. doi: 10.1074/jbc.M111.226027. Epub 2011 May 16.
The highly sulfated polysaccharides heparin and heparan sulfate (HS) play key roles in the regulation of physiological and pathophysiological processes. Despite its importance, no molecular structures of free HS have been reported up to now. By combining analytical ultracentrifugation, small angle x-ray scattering, and constrained scattering modeling recently used for heparin, we have analyzed the solution structures for eight purified HS fragments degree of polymerization 6-18 (dp6-dp18) and dp24, corresponding to the predominantly unsulfated GlcA-GlcNAc domains of heparan sulfate. Unlike heparin, the sedimentation coefficient s(20,)(w) of HS dp6-dp24 showed a small rotor speed dependence, where similar s(20,)(w) values of 0.82-1.26 S (absorbance optics) and 1.05-1.34 S (interference optics) were determined. The corresponding x-ray scattering measurements of HS dp6-dp24 gave radius of gyration (R(G)) values from 1.03 to 2.82 nm, cross-sectional radius of gyration (R(XS)) values from 0.31 to 0.65 nm, and maximum lengths (L) from 3.0 to 10.0 nm. These data showed that HS has a longer and more bent structure than heparin. Constrained scattering modeling starting from 5000-8000 conformationally randomized HS structures gave best fit dp6-dp16 molecular structures that were longer and more bent than their equivalents in heparin. No fits were obtained for HS dp18 or dp24, indicating their higher flexibility. We conclude that HS displays an extended bent conformation that is significantly distinct from that for heparin. The difference is attributed to the different predominant monosaccharide sequence and reduced sulfation of HS, indicating that HS may interact differently with proteins compared with heparin.
高度硫酸化的多糖肝素和硫酸乙酰肝素 (HS) 在调节生理和病理生理过程中发挥着关键作用。尽管其重要性不言而喻，但迄今为止尚未报道过游离 HS 的分子结构。通过结合最近用于肝素的分析超速离心、小角 X 射线散射和约束散射建模，我们分析了 8 个纯化的 HS 片段（聚合度为 6-18[dp6-dp18]和 dp24）的溶液结构，这些片段对应于硫酸乙酰肝素中主要未硫酸化的 GlcA-GlcNAc 结构域。与肝素不同，HS dp6-dp24 的沉降系数 s(20,)(w) 对转子转速的依赖性较小，通过吸收光学法和干涉光学法确定了相似的 s(20,)(w) 值 0.82-1.26 S 和 1.05-1.34 S。HS dp6-dp24 的相应 X 射线散射测量给出了回转半径 (R(G)) 值从 1.03 到 2.82 nm，截面回转半径 (R(XS)) 值从 0.31 到 0.65 nm，最大长度 (L) 从 3.0 到 10.0 nm。这些数据表明 HS 具有比肝素更长且更弯曲的结构。从 5000-8000 个构象随机化的 HS 结构开始的约束散射建模给出了最佳拟合的 dp6-dp16 分子结构，其长度和弯曲度均大于肝素中的相应结构。未获得 HS dp18 或 dp24 的拟合结果，表明其具有更高的灵活性。我们得出结论，HS 表现出伸展的弯曲构象，与肝素的构象明显不同。这种差异归因于 HS 中不同的主要单糖序列和较低的硫酸化程度，表明 HS 与蛋白质的相互作用可能与肝素不同。
