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首页> 美国卫生研究院文献>other >Two-dimensional NMR Spectroscopy and Structures of Six Lipid A Species from Rhizobium etli CE3 DETECTION OF AN ACYLOXYACYL RESIDUE IN EACH COMPONENT AND ORIGIN OF THE AMINOGLUCONATE MOIETY
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Two-dimensional NMR Spectroscopy and Structures of Six Lipid A Species from Rhizobium etli CE3 DETECTION OF AN ACYLOXYACYL RESIDUE IN EACH COMPONENT AND ORIGIN OF THE AMINOGLUCONATE MOIETY

机译：氨基葡糖部分的每个成分和来源中的根瘤菌CE3六种脂质A的二维NMR光谱和结构检测酰氧基残基

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摘要

The chemical structures of six lipid A species (A, B, C, D-1, D-2, and E) purified from Rhizobium etli CE3 were investigated by one- and two-dimensional NMR spectroscopy. The R. etli lipid A subtypes each contain an unusual acyloxyacyl residue at position 2′ as part of a conserved distal glucosamine moiety but differ in their proximal units. All R. etli lipid A species lack phosphate groups. However, they are derivatized with an α-linked galacturonic acid group at position 4′, as shown by nuclear Overhauser effect spectroscopy. Component B, which had been not been reported in previous studies, features a β, 1′-6 linked disaccharide of glucosamine acylated at positions 2, 3, 2′, and 3′ in a pattern that is typical of lipid A found in other Gram-negative bacteria. D-1 contains an acylated aminogluconate unit in place of the proximal glucosamine residue of B. C and E lack ester-linked β-hydroxyacyl chains at position 3, as judged by their H-3 chemical shifts, and may be synthesized from B and D-1, respectively, by the R. etli 3-O-deacylase. D-2 is an isomer of D-1 that forms nonenzymatically by acyl chain migration. A may be an elimination product derived from D-1 during hydrolysis at 100 °C (pH 4.5), a step needed to release lipid A from lipopolysaccharide. Based on these findings, we propose a biosynthetic scheme for R. etli lipid A in which B is generated first by a variation of the E. coli pathway. The aminogluconate unit of D-1 could then be made from B by enzymatic oxidation of the proximal glucosamine. As predicted by our hypothesis, enzyme(s) can be demonstrated in extracts of R. etli that convert 14C-labeled B to D-1.
机译：通过一维和二维NMR光谱研究了从根瘤菌CE3纯化的六个脂质A种类（A，B，C，D-1，D-2和E）的化学结构。 R. etli脂质A亚型各自在位置2'处包含一个不寻常的酰氧基酰基残基，作为保守的远端葡糖胺部分的一部分，但它们的近端单元不同。所有的R. etli脂质A种类都没有磷酸基团。然而，如核Overhauser效应光谱法所示，它们在位置4'被α-连接的半乳​​糖醛酸基团衍生。先前研究中尚未报道的组分B的特征是，在位置2、3、2'和3'上的氨基葡萄糖的β，1'-6连接的二糖被酰化，其模式类似于在其他脂质中发现的脂质A。革兰氏阴性细菌。 D-1含有酰化的氨基葡萄糖酸酯单元，取代了B的近端氨基葡萄糖残基。C和E的H-3化学位移可判断其在3位上没有酯键连接的β-羟酰基链，可以由B和D-1分别由R. etli 3-O-脱酰基酶。 D-2是D-1的异构体，通过酰基链迁移以非酶形式形成。 A可能是在100°C（pH 4.5）水解过程中衍生自D-1的消除产物，该步骤是从脂多糖释放脂质A的步骤。基于这些发现，我们提出了一种R. etli脂质A的生物合成方案，其中B是首先通过大肠杆菌途径的变化而产生的。然后，D-1的氨基葡萄糖酸酯单元可以由B通过近端葡萄糖胺的酶促氧化制得。正如我们的假设所预测的，酶可以在R. etli的提取物中得到证明，这些提取物将 14 C标记的B转化为D-1。

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