EVIDENCE FOR CONFORMATIONAL EQUILIBRIUM OF THE SULFATED L-IDURONATE RESIDUE IN HEPARIN AND IN SYNTHETIC HEPARIN MONOSACCHARIDES AND OLIGOSACCHARIDES - NMR AND FORCE-FIELD STUDIES
EVIDENCE FOR CONFORMATIONAL EQUILIBRIUM OF THE SULFATED L-IDURONATE RESIDUE IN HEPARIN AND IN SYNTHETIC HEPARIN MONOSACCHARIDES AND OLIGOSACCHARIDES - NMR AND FORCE-FIELD STUDIES
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DOI：
10.1021/ja00281a052
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发表时间：
1986-10-15
影响因子：
15
通讯作者：
CHOAY, J
中科院分区：
文献类型：
--
作者：
FERRO, DR;PROVASOLI, A;CHOAY, J
通过1H NMR研究了硫酸l -伊杜醛酸（I2S）在不同肝素序列中的构象，包括代表抗凝血酶III （AT-III）结合位点的特定五糖序列。对于单体甲基- 2- o-磺。-L-iduronate相邻质子间耦合常数都很小（1.8-3.4 Hz），占1C4椅的主要贡献。相比之下，当I2S插入两个N，6-二磺酸d -氨基葡萄糖残基之间时，一些偶联（特别是j2,3）变得更大（高达6 Hz），就像肝素的常规序列一样，当I2S被AT-III结合位点典型的N，3,6-三磺酸d -氨基葡萄糖残基糖基化时，偶联甚至更大（高达7.5 Hz）。用力场法计算了I2S （1C4、2S0和4C1）的质子间偶联常数，并计算了它们在不同肝素序列上的近似等能构象。基于能量的考虑，其他构象被抛弃了。采用最小二乘拟合方法，将共形体混合的平均耦合常数与观测值拟合得到共形体种群。当I2S是规则肝素序列的一部分时，2So的斜船形成为重要的贡献者(.apprx。40%)到硫酸化的伊杜酸残基的构象。当使I2S糖基化的氨基糖残基被三硫化时（如AT-III的结合位点），2S0成为优势（约60%）。力场计算表明，这种向2S0构象的驱动与独特的3-硫酸盐基团的静电效应有关。
The conformation of sulfated L-iduronic acid (I2S) in different heparin sequences, including the specific pentasaccharide sequence representing the binding site to antithrombin III (AT-III), was investigated by 1H NMR spectroscopy on suitable synthetic mono- and oligosaccharides. For the monomer methyl 2-O-sulfo-.alpha.-L-iduronate vicinal interproton coupling constants are all small (1.8-3.4 Hz), accounting for a predominant contribution of a 1C4 chair. By contrast, some couplings (especially J2,3) become larger (up to 6 Hz) when I2S is inserted between two N,6-disulfated D-glucosamine residues as occurring in the regular sequences of heparin, and even larger (up to 7.5 Hz) when I2S is glycosylated by the N,3,6-trisulfated D-glucosamine residues typical of the binding site to AT-III. The interproton coupling constants of the individual, nearly isoenergetic conformers of I2S (1C4, 2S0, and 4C1) were evaluated for different heparin sequences by using molecular geometries obtained by a force field method. Other conformations were discarded on the basis of energy considerations. The conformer populations were obtained by least-squares fitting the average computed coupling constants of the conformer mixture to the observed values. When I2S is part of regular heparin sequences, the skew-boat form 2So becomes an important contributor (.apprx. 40%) to the conformation of the sulfated iduronate residues. When the amino sugar residues glycosylating the I2S is trisulfated (as in the binding site to AT-III), 2S0 becomes predominant (> 60%). Force field calculations suggest that such a drive toward the 2S0 conformation is associated with electrostatic effects of the unique 3-sulfate group.