Department of Chemistry, Kyungpook National University, Daegu, Republic of Korea.
J Biol Inorg Chem. 2010 Feb;15(2):175-82. doi: 10.1007/s00775-009-0581-x. Epub 2009 Aug 26.
Superoxide dismutases (SODs) protect cells against oxidative stress by disproportionating O2(-) to H(2)O(2) and O(2). The recent finding of a nickel-containing SOD (Ni-SOD) has widened the diversity of SODs in terms of metal contents and SOD catalytic mechanisms. The coordination and geometrical structure of the metal site and the related electronic structure are the keys to understanding the dismutase mechanism of the enzyme. We performed Q-band (14)N,(1/2)H continuous wave (CW) and pulsed electron-nuclear double resonance (ENDOR) and X-band (14)N electron spin echo envelope modulation (ESEEM) on the resting-state Ni-SOD extracted from Streptomyces seoulensis. In-depth analysis of the data obtained from the multifrequency advanced electron paramagnetic resonance techniques detailed the electronic structure of the active site of Ni-SOD. The analysis of the field-dependent Q-band (14)N CW ENDOR yielded the nuclear hyperfine and quadrupole coupling tensors of the axial N(delta) of the His-1 imidazole ligand. The tensors are coaxial with the g-tensor frame, implying the g-tensor direction is modulated by the imidazole plane. X-band (14)N ESEEM characterized the hyperfine coupling of N(epsilon) of His-1 imidazole. The nuclear quadrupole coupling constant of the nitrogen suggests that the hydrogen-bonding between N(epsilon)-H and O(Glu-17) present for the reduced-state Ni-SOD is weakened or broken upon oxidizing the enzyme. Q-band (1)H CW ENDOR and pulsed (2)H Mims ENDOR showed a strong hyperfine coupling to the protons(s) of the equatorially coordinated His-1 amine and a weak hyperfine coupling to either the proton(s) of a water in the pocket at the side opposite the axial N(delta) or the proton of a water hydrogen-bonded to the equatorial thiolate ligand.
超氧化物歧化酶（SODs）通过将 O2(-)歧化为 H2O2 和 O2 来保护细胞免受氧化应激。最近发现的一种含镍的 SOD（Ni-SOD）拓宽了 SOD 的多样性，涉及金属含量和 SOD 催化机制。金属位点的配位和几何结构以及相关的电子结构是理解酶歧化酶机制的关键。我们对从链霉菌属中提取的处于静止状态的 Ni-SOD 进行了 Q 波段（14）N，（1/2）H 连续波（CW）和脉冲电子-核双共振（ENDOR）以及 X 波段（14）N 电子自旋回波调制（ESEEM）实验。来自多频先进电子顺磁共振技术的数据的深入分析详细描述了 Ni-SOD 活性位点的电子结构。对场依赖的 Q 波段（14）N CW ENDOR 的分析得到了轴向 N(delta)的 His-1 咪唑配体的核超精细和四极偶合张量。张量与 g-张量框架同轴，表明 g-张量方向被咪唑平面调制。X 波段（14）N ESEEM 表征了 His-1 咪唑的 N(epsilon)的超精细耦合。氮的核四极偶合常数表明，对于还原态 Ni-SOD，N(epsilon)-H 和 O(Glu-17)之间的氢键在氧化酶时减弱或断裂。Q 波段（1）H CW ENDOR 和脉冲（2）H Mims ENDOR 显示与赤道配位的 His-1 胺的质子（s）具有很强的超精细耦合，与口袋中位于轴向 N(delta)相反一侧的水的质子（s）或与赤道硫醇配体氢键合的水的质子具有较弱的超精细耦合。
