Comparison and contrasts between the active site PKs of Mn-superoxide dismutase and those of Fe-superoxide dismutase.
Comparison and contrasts between the active site PKs of Mn-superoxide dismutase and those of Fe-superoxide dismutase.
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DOI：
10.1021/ja027319z
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发表时间：
2002-11
影响因子：
15
通讯作者：
J. Maliekal;A. Karapetian;C. Vance;Emine Yikilmaz;Qiang Wu;Timothy A. Jackson;T. Brunold;T. Spiro;Anne‐Frances Miller
中科院分区：
文献类型：
--
作者：
J. Maliekal;A. Karapetian;C. Vance;Emine Yikilmaz;Qiang Wu;Timothy A. Jackson;T. Brunold;T. Spiro;Anne‐Frances Miller
含铁和锰的超氧化物歧化酶催化相同的反应，并具有几乎重叠的活性位点。因此，假定其机制的细节相似。然而，我们现在表明，大肠杆菌MnSOD活性的pH依赖性反映了不同的活性位点质子平衡（氧化）Mn（3+）SOD比的事件，影响活性位点pK的氧化FeSOD。我们发现，在Fe（3+）SOD中pK高于11.5的普遍保守的Tyr 34负责Mn（3+）SOD的pK接近9.5，因此，Mn（3+）SOD的氧化态pK对应于外球事件，而Fe（3+）SOD的氧化态pK对应于内球事件[Bull，C.;费，J.A. J. Am. 1985，107，3295-3304]。我们还提出了第一个描述的还原态pK MnSOD。Mn（2+）SOD的pK涉及Tyr 34的去质子化，Fe（2+）SOD的pK也是如此[Sorkin，D. L.的;米勒A.- F. Biochemistry 1997，36，4916-4924]。然而，分别为10.5和8.5的pK值是相当不同的，并且Mn（2+）SOD的pK影响Mn（2+）的配位几何形状，最可能是通过保守的Gln 146的极化，该Gln 146与轴向配位的H（2）O形成氢键。我们的发现与Mn（2+/3+）与Fe（2+/3+）的不同电子构型一致，例如MnSOD中Gln 146与配位溶剂之间的氢键比FeSOD中类似的Gln 69与配位溶剂之间的氢键更强，以及Mn（2+）SOD中Mn（2+）的第六配位位点附近存在弱局部H（2）O [Borgstahl等人，J. Mol. Biol. 2000，296，951-959]。
The Fe- and Mn-containing superoxide dismutases catalize the same reaction and have almost superimposable active sites. Therefore, the details of their mechanisms have been assumed to be similar. However, we now show that the pH dependence of Escherichia coli MnSOD activity reflects a different active site proton equilibrium in (oxidized) Mn(3+)SOD than the event that affects the active site pK of oxidized FeSOD. We find that the universally conserved Tyr34 that has a pK above 11.5 in Fe(3+)SOD is responsible for the pK near 9.5 of Mn(3+)SOD and, thus, that the oxidized state pK of Mn(3+)SOD corresponds to an outer-sphere event whereas that of Fe(3+)SOD corresponds to an inner sphere event [Bull, C.; Fee, J. A. J. Am. Chem. Soc. 1985, 107, 3295-3304]. We also present the first description of a reduced-state pK for MnSOD. Mn(2+)SOD's pK involves deprotonation of Tyr34, as does Fe(2+)SOD's pK [Sorkin, D. L.; Miller A.-F. Biochemistry 1997, 36, 4916-4924]. However, the values of the pKs, 10.5 and 8.5 respectively, are quite different and Mn(2+)SOD's pK affects the coordination geometry of Mn(2+), most likely via polarization of the conserved Gln146 that hydrogen bonds to axially coordinated H(2)O. Our findings are consistent with the different electronic configurations of Mn(2+/3+) vs Fe(2+/3+), such as the stronger hydrogen bonding between Gln146 and coordinated solvent in MnSOD than that between the analogous Gln69 and coordinated solvent in FeSOD, and the existence of weakly localized H(2)O near the sixth coordination site of Mn(2+) in Mn(2+)SOD [Borgstahl et al. J. Mol. Biol. 2000, 296, 951-959].