Silipo Alba, Zhang Zhenqing, Cañada F Javier, Molinaro Antonio, Linhardt Robert J, Jiménez-Barbero Jesús
Centro de Investigaciones Biològicas, CSIC, Ramiro de Maeztu 9,28040 Madrid, Spain.
Chembiochem. 2008 Jan 25;9(2):240-52. doi: 10.1002/cbic.200700400.
The solution conformation behavior of a dermatan-derived tetrasaccharide--Delta HexA-(1-->3)-GalNAc4S-beta-(1-->4)-IdoA-alpha-(1-->3)-red-GalNAc4S (S is a sulfate group)--has been explored by means of NMR spectroscopy, especially by NOE-based conformational analysis. The tetrasaccharide was present as four species, two of which are chemically different in the anomeric orientation of the reducing 2-deoxy-2-acetamido-galactose (red-GalNAc) residue, while the other two are the result of different conformations of the iduronic acid (IdoA) unit. The two alpha-beta-interconverting anomers were present in a 0.6:1 ratio. Ring conformations have been defined by analysis of (3)J(H,H) coupling constants and interresidual NOE contacts. Both 2-deoxy-2-acetamido-galactose (GalNAc) residues were found in the (4)C(1) chair conformation, the unsaturated uronic acid (Delta-Hex A) adopts a strongly predominant half-chair (1)H(2) conformation, while the IdoA residue exists either in the (1)C(4) chair or in the (2)S(0) skewed boat geometries, in a 4:1 ratio. There is a moderate flexibility of Phi and Psi torsions as suggested by nuclear Overhauser effects (NOEs), molecular modeling (MM), and molecular dynamics (MD) studies. This was further investigated by residual dipolar couplings (RDCs). One-bond C--H RDCs ((1)D(C,H)) and long-range H-H ((3)D(H,H)) RDCs were measured for the tetrasaccharide in a phage solution and interpreted in combination with restrained MD simulation. The RDC-derived data substantially confirmed the validity of the conformer distribution resulting from the NOE-derived simulations, but allowed an improved definition of the conformational behavior of the oligosaccharides in solution. In summary, the data show a moderate flexibility of the four tetrasaccharide species at the central glycosidic linkage. Differences in the shapes of species with the IdoA in skew and in chair conformations and in the distribution of the sulfate groups have also been highlighted.
已通过核磁共振光谱法，特别是基于核Overhauser效应（NOE）的构象分析，探究了一种源自硫酸皮肤素的四糖——ΔHexA-(1→3)-GalNAc4S-β-(1→4)-IdoA-α-(1→3)-red-GalNAc4S（S为硫酸基团）的溶液构象行为。该四糖以四种形式存在，其中两种在还原型2-脱氧-2-乙酰氨基半乳糖（red-GalNAc）残基的异头构型上存在化学差异，而另外两种则是艾杜糖醛酸（IdoA）单元不同构象的结果。两种α-β互变端基异构体的比例为0.6:1。通过分析(3)J(H,H)耦合常数和残基间NOE接触来确定环构象。发现两个2-脱氧-2-乙酰氨基半乳糖（GalNAc）残基均处于(4)C(1)椅式构象，不饱和糖醛酸（Δ-Hex A）主要采取半椅式(1)H(2)构象，而IdoA残基以4:1的比例存在于(1)C(4)椅式或(2)S(0)扭船式几何构象中。如核Overhauser效应（NOEs）、分子建模（MM）和分子动力学（MD）研究所表明的，Phi和Psi扭转具有适度的灵活性。通过残余偶极耦合（RDCs）对此进行了进一步研究。在噬菌体溶液中测量了该四糖的一键C-H RDCs（(1)D(C,H)）和远程H-H（(3)D(H,H)）RDCs，并结合受限MD模拟进行了解释。RDC衍生的数据充分证实了由NOE衍生模拟得出的构象异构体分布的有效性，但有助于更好地定义寡糖在溶液中的构象行为。总之，数据表明这四种四糖物种在中心糖苷键处具有适度的灵活性。还突出显示了IdoA处于扭船式和椅式构象的物种形状差异以及硫酸基团的分布差异。
