XAS investigation of the structure and function of Ni in acireductone dioxygenase
XAS investigation of the structure and function of Ni in acireductone dioxygenase
复制标题
DOI：
10.1021/bi012209a
复制
发表时间：
2002-05-28
期刊：
影响因子：
2.9
通讯作者：
Maroney, MJ
中科院分区：
文献类型：
--
作者：
Al-Mjeni, F;Ju, T;Maroney, MJ
乙酰丙酮双加氧酶 (ARD) 是参与蛋氨酸循环途径的酶，可调节细胞周期的各个方面。肺炎克雷伯菌产生两种酶，它们具有共同的多肽序列，仅存在的金属离子不同。 Acireductone（1,2-二羟基-3-酮基-5-甲基硫代戊烯）与 Fe-ARD 和分子氧反应生成甲酸和 2-酮基-4-甲基硫代丁酸（甲硫氨酸的 α-酮酸前体）。 Ni-ARD 与 acreductone 和分子氧反应生成硫代丙酸甲酯、CO 和甲酸盐，并且不位于蛋氨酸循环途径中。报道了对静止 Ni-ARD 酶和酶-底物复合物中催化 Ni 中心结构的 X 射线吸收光谱 (XAS) 研究。本研究建立了静息 Ni-ARD 中 Ni 位点的结构，包含由 O/N 供体配体（包括 3-4 个组氨酸残基）组成的六配位 Ni 位点，证明底物通过置换两个配体（其中至少一个是组氨酸配体）以双齿方式与 Ni 中心结合，并深入了解含 Ni 双加氧酶所采用的催化机制。在 Ni-ARD 的 H-1 核磁共振谱中观察到有效弛豫和超精细位移共振，这可归因于 His 咪唑连接顺磁性 Ni 离子，并且与 His 连接的 XAS 结果一致。这些共振在底物存在的情况下显示出显着的扰动，证实金属离子直接与底物相互作用。
Acireductone dioxygenases (ARDs) are enzymes involved in the methionine recycle pathway, which regulates aspects of the cell cycle. Klebsiella pneumoniae produces two enzymes that share a common polypeptide sequence and differ only in the metal ion present. Reaction of acireductone (1,2-dihydroxy-3-keto-5-methylthiopentene) with Fe-ARD and dioxygen produces formate and 2-keto-4-methylthiobutanoic acid, the alpha-ketoacid precursor of methionine. Ni-ARD reacts with acireductone and dioxygen to produce methylthiopropionate, CO, and formate and does not lie on the methionine recycle pathway. An X-ray absorption spectroscopy (XAS) study of the structure of the catalytic Ni center in resting Ni-ARD enzyme and the enzyme-substrate complex is reported. This study establishes the structure of the Ni site in resting Ni-ARD as containing a six coordinate Ni site composed of O/N-donor ligands including 3-4 histidine residues, demonstrates that the substrate binds to the Ni center in a bidentate fashion by displacing two ligands, at least one of which is a histidine ligand, and provides insight into the mechanism of catalysis employed by a Ni-containing dioxygenase. Efficiently relaxed and hyperfine-shifted resonances are observed in the H-1 nuclear magnetic resonance spectrum of Ni-ARD that can be attributed to the His imidazoles ligating the paramagnetic Ni ion and are consistent with the XAS results regarding His ligation. These resonances show significant perturbation in the presence of substrate, confirming that the metal ion interacts directly with the substrate.