Abstract

Chondroitinase ABC I (cABC-I) is the enzyme which cleaves the β-1,4 glycosidic linkage of chondroitin sulfate (CS) by β-elimination. To elucidate more accurately the substrate specificity of cABC-I, we evaluated the kinetic parameters of cABC-I and its reactivity with CS isomers displaying less structural heterogeneity as substrates, e.g., approximately 90 percent of disaccharide units in Chondroitin sulfate A (CSA) or Chondroitin sulfate C (CSC) is D-glucuronic acid and 4-O-sulfated N-acetyl galactosamine (GalNAc) (A-unit) or D-glucuronic acid and 6-O-sulfated GalNAc (C-unit), respectively. cABC-I showed the highest reactivity to CSA and CSC among all CS isomers, and the k_cat/K_m of cABC-I was higher for CSA than for CSC. Next, we determined the crystal structures of cABC-I in complex with CS disaccharides, and analyzed the crystallographic data in combination with molecular docking data. Arg500 interacts with 4-O-sulfated and 6-O-sulfated GalNAc residues. The distance between Arg500 and the 4-O-sulfate group was 0.8 Å shorter than that between Arg500 and the 6-O-sulfated group. Moreover, it is likely that the 6-O-sulfated group is electrostatically repulsed by the nearby Asp490. Thus, we demonstrated that cABC-I has the highest affinity for the CSA richest in 4-O-sulfated GalNAc residues among all CS isomers. Recently, cABC-I was used to treat lumbar disc herniation. The results provide useful information to understand the mechanism of the pharmacological action of cABC-I.

中文翻译：

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基于与二糖复合物的生化反应和晶体结构分析的软骨素酶 ABC I 的底物特异性

摘要

软骨素酶 ABC I (cABC-I) 是通过 β-消除来切割硫酸软骨素 (CS) 的 β-1,4 糖苷键的酶。为了更准确地阐明 cABC-I 的底物特异性，我们评估了 cABC-I 的动力学参数及其与作为底物显示较少结构异质性的 CS 异构体的反应性，例如硫酸软骨素 A (CSA) 中约 90% 的二糖单元或硫酸软骨素 C (CSC) 分别是 D-葡萄糖醛酸和 4- O-硫酸化N-乙酰半乳糖胺 (GalNAc)（A-单元）或 D-葡萄糖醛酸和 6- O-硫酸化 GalNAc（C-单元）。cABC-I 在所有 CS 异构体中对 CSA 和 CSC 的反应性最高，k _cat / K _mCSA 的 cABC-I 比 CSC 高。接下来，我们确定了与 CS 二糖复合的 cABC-I 的晶体结构，并结合分子对接数据分析了晶体学数据。Arg500 与 4- O-硫酸化和 6 - O-硫酸化 GalNAc 残基相互作用。Arg500 和 4-O-硫酸盐基团之间的距离比Arg500 和 6- O-硫酸盐基团之间的距离短 0.8 Å。此外，6 - O-硫酸化基团很可能被附近的 Asp490 静电排斥。因此，我们证明了 cABC-I 对富含 4- O的 CSA 具有最高的亲和力。所有 CS 异构体中的硫酸化 GalNAc 残基。最近，cABC-I被用于治疗腰椎间盘突出症。该结果为了解 cABC-I 的药理作用机制提供了有用的信息。