Hyaluronan: the absence of amide-carboxylate hydrogen bonds and the chain conformation in aqueous solution are incompatible with stable secondary and tertiary structure models
Hyaluronan: the absence of amide-carboxylate hydrogen bonds and the chain conformation in aqueous solution are incompatible with stable secondary and tertiary structure models
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DOI：
10.1042/bj20060085
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发表时间：
2006-06-15
影响因子：
4.1
通讯作者：
Almond, Andrew
中科院分区：
文献类型：
--
作者：
Blundell, Charles D.;DeAngelis, Paul L.;Almond, Andrew
文献中对糖胺聚糖透明质酸（HA）水溶液构象的描述存在矛盾。根据流体动力学和模拟数据，HA分子在局部水平上通过快速交换的瞬态氢键网络加强，而在全局水平上没有明显的关联。与此形成鲜明对比的是，从核磁共振数据中得出的模型表明，二级结构包括持久的氢键，并且链之间的强关联可以形成巨大的稳定的三级结构。这些模型需要一个扩展的2倍螺旋构象的HA链和特定的氢键之间的酰胺和羧酸基团。为了验证这些描述，我们使用n -15标记的低聚糖和高场核磁共振来测量对乙酰氨基基团的相关性质。酰胺质子化学位移摄动和羧酸基pK(a)值与酰胺和羧酸基之间高度密集的氢键不一致。酰胺质子温度系数和化学交换速率证实了这一结论。低聚物与聚合物HA的性质比较表明，在八糖中心和聚合物之间的酰胺质子环境没有明显的差异，与三级结构的形成不一致。在HA八糖上记录的[H-1-H-1-N-15] noesi - hsqc（异核单量子相关）光谱显示，中心的酰胺基团呈反取向，平均溶液构象不是延长的2倍螺旋。因此，二级和三级结构模型的两个关键方面不太可能是正确的。相反，这些新的核磁共振数据与水动力和模拟数据的描述一致。
Contradictory descriptions for the aqueous solution conformation of the glycosaminoglycan hyaluronan (HA) exist in the literature. According to hydrodynamic and simulation data, HA molecules are stiffened by a rapidly interchanging network of transient hydrogen bonds at the local level and do not significantly associate at the global level. In marked contrast, models derived from NMR data suggest that the secondary structure involves persistent hydrogen bonds and that strong associations between chains can occur to form vast stable tertiary structures. These models require an extended 2-fold helical conformation of the HA chain and specific hydrogen bonds between amide and carboxylate groups. To test these descriptions, we have used N-15-labelled oligosaccharides and high-field NMR to measure pertinent properties of the acetamido group. The amide proton chemical shift perturbation and carboxylate group pK(a) value are inconsistent with a highly populated hydrogen bond between the amide and carboxylate groups. Amide proton temperature coefficients and chemical exchange rates confirm this conclusion. Comparison of oligomer properties with polymeric HA indicates that there is no discernible difference in amide proton environment between the centre of octasaccharides and the polymer, inconsistent with the formation of tertiary structures. A [H-1-H-1-N-15] NOESY-HSQC (heteronuclear single-quantum correlation) spectrum recorded on an HA octasaccharide revealed that amide groups in the centre are in a trans orientation and that the average solution conformation is not an extended 2-fold helix. Therefore the two key aspects of the secondary and tertiary structure models are unlikely to be correct. Rather, these new NMR data agree with descriptions from hydrodynamic and simulations data.