The orbital ground state of the azide-substrate complex of human heme oxygenase is an indicator of distal H-bonding: implications for the enzyme mechanism.
The orbital ground state of the azide-substrate complex of human heme oxygenase is an indicator of distal H-bonding: implications for the enzyme mechanism.
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DOI：
10.1021/bi802360g
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发表时间：
2009-04-14
期刊：
影响因子：
2.9
通讯作者：
La Mar, Gerd N.
中科院分区：
文献类型：
--
作者：
Ogura, Hiroshi;Evans, John P.;Peng, Dungeng;Satterlee, James D.;de Montellano, Paul R. Ortiz;La Mar, Gerd N.
底物结合的人血红素加氧酶-1（hHO）的叠氮化物复合物的活性位点的电子结构已通过1H NMR光谱研究，揭示了轨道/自旋基态作为酶的独特的远端口袋环境的指标。底物和底物接触残基信号的2D 1H NMR分配揭示了底物甲基接触位移的模式，其将孤铁π-自旋置于dxz轨道中，而不是在氰化物络合物中发现的dyz轨道。铁的自旋弛豫率，磁各向异性和磁化率的比较认为，低自旋，（dxy）2（dyz，dxz）3，在叠氮化物和氰化物的配合物的基态。从氰化物的单占据dyz到hHO的叠氮化物复合物的dxz的转换被证明与由后者复合物中的叠氮化物π平面确定的轨道空穴一致，后者在平面内从咪唑π平面旋转了约90°。在叠氮化物中相对于氰化物HHO复合物的改变的轨道基态的诱导，以及甲基超精细位移的平均低场偏置和它们相对于球蛋白中的顺磁弛豫率，表明叠氮化物在HHO中比在球蛋白中施加更强的配体场，或者叠氮化物的远端氢键在HHO中比在球蛋白中弱。消除活性的Asp 140 → Ala hHO突变体保留了不寻常的WT叠氮化物复合物自旋/轨道基态。我们的研究结果为其他HO复合物和HO机制的相关性进行了讨论。
The active site electronic structure of the azide complex of substrate-bound human heme oxygenase-1, (hHO) has been investigated by 1H NMR spectroscopy to shed light on the orbital/spin ground state as an indicator of the unique distal pocket environment of the enzyme. 2D 1H NMR assignments of the substrate and substrate-contact residue signals reveal a pattern of substrate methyl contact shifts, that places the lone iron π-spin in the dxz orbital, rather than the dyz orbital found in the cyanide complex. Comparison of iron spin relaxivity, magnetic anisotropy and magnetic susceptibilities argues for a low-spin, (dxy)2(dyz,dxz)3, ground state in both azide and cyanide complexes. The switch from singly-occupied dyz for the cyanide to dxz for the azide complex of hHO is shown to be consistent with the orbital hole determined by the azide π-plane in the latter complex, which is ∼90° in-plane rotated from that of the imidazole π-plane. The induction of the altered orbital ground state in the azide relative to the cyanide hHO complex, as well as the mean low-field bias of methyl hyperfine shifts and their paramagnetic relaxivity relative to those in globins, indicate that azide exerts a stronger ligand field in hHO than in the globins, or that the distal H-bonding to azide is weaker in hHO than in globins. The Asp140 → Ala hHO mutant that abolishes activity retains the unusual WT azide complex spin/orbital ground state. The relevance of our findings for other HO complexes and the HO mechanism is discussed.
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影响因子：
2.9
作者：
HERNANDEZ, G;WILKS, A;LAMAR, GN
通讯作者：
LAMAR, GN
影响因子：
15
作者：
Caignan, GA;Deshmukh, R;Rivera, M
通讯作者：
Rivera, M
影响因子：
15
作者：
Fujii, H;Zhang, XH;Yoshida, T
通讯作者：
Yoshida, T
DOI：
10.1016/0005-2795(69)90250-5
发表时间：
1969-01-01
期刊：
BIOCHIMICA ET BIOPHYSICA ACTA
影响因子：
--
作者：
IIZUKA, T;KOTANI, M
通讯作者：
KOTANI, M
影响因子：
15
作者：
Kumar, D;de Visser, SP;Shaik, S
通讯作者：
Shaik, S