Mathé Christelle, Nivière Vincent, Houée-Levin Chantal, Mattioli Tony A
Laboratoire de Biophysique du Stress Oxydant, SBE and CNRS URA 2096, Département de Biologie Joliot Curie, CEA Saclay, 91191 Gif-sur-Yvette cedex, France.
Biophys Chem. 2006 Jan 1;119(1):38-48. doi: 10.1016/j.bpc.2005.06.013. Epub 2005 Aug 9.
Superoxide reductases (SORs) are superoxide (O2-)-detoxifying enzymes that catalyse the reduction of O2- into hydrogen peroxide. Three different classes of SOR have been reported on the basis of the presence or not of an additional N-terminal domain. They all share a similar active site, with an unusual non-heme Fe atom coordinated by four equatorial histidines and one axial cysteine residues. Crucial catalytic reaction intermediates of SOR are purported to be Fe(3+)-(hydro)peroxo species. Using resonance Raman spectroscopy, we compared the vibrational properties of the Fe3+ active site of two different classes of SOR, from Desulfoarculus baarsii and Treponema pallidum, along with their ferrocyanide and their peroxo complexes. In both species, rapid treatment with H2O2 results in the stabilization of a side-on high spin Fe(3+)-(eta(2)-OO) peroxo species. Comparison of these two peroxo species reveals significant differences in vibrational frequencies and bond strengths of the Fe-O2 (weaker) and O-O (stronger) bonds for the T. pallidum enzyme. Thus, the two peroxo adducts in these two SORs have different stabilities which are also seen to be correlated with differences in the Fe-S coordination strengths as gauged by the Fe-S vibrational frequencies. This was interpreted from structural variations in the two active sites, resulting in differences in the electron donating properties of the trans cysteine ligand. Our results suggest that the structural differences observed in the active site of different classes of SORs should be a determining factor for the rate of release of the iron-peroxo intermediate during enzymatic turnover.
超氧化物还原酶（SORs）是一类能够解毒超氧化物（O2-）的酶，可催化将O2-还原为过氧化氢。根据是否存在额外的N端结构域，已报道了三种不同类型的SOR。它们都具有相似的活性位点，其中一个不寻常的非血红素铁原子由四个赤道面组氨酸和一个轴向半胱氨酸残基配位。SOR的关键催化反应中间体据推测是Fe(3+)-(氢)过氧物种。我们使用共振拉曼光谱法，比较了来自巴氏脱硫弧菌和梅毒螺旋体的两种不同类型SOR的Fe3+活性位点及其亚铁氰化物和过氧配合物的振动特性。在这两种物种中，用H2O2快速处理会导致侧接高自旋Fe(3+)-(η(2)-OO)过氧物种的稳定。对这两种过氧物种的比较揭示了梅毒螺旋体酶在Fe-O2（较弱）和O-O（较强）键的振动频率和键强度上存在显著差异。因此，这两种SOR中的两种过氧加合物具有不同的稳定性，这也与通过Fe-S振动频率衡量的Fe-S配位强度差异相关。这是根据两个活性位点的结构变化来解释的，导致反式半胱氨酸配体的供电子性质存在差异。我们的结果表明，在不同类型SOR的活性位点观察到的结构差异应该是酶促周转过程中铁过氧中间体释放速率的决定因素。
