Weitz Andrew C, Biswas Saborni, Rizzolo Kim, Elliott Sean, Bominaar Emile L, Hendrich Michael P
Department of Chemistry, Boston University, Boston, Massachusetts 02215, United States.
Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States.
Inorg Chem. 2020 Jul 20;59(14):10223-10233. doi: 10.1021/acs.inorgchem.0c01349. Epub 2020 Jun 30.
The BthA protein from the microorganism contains two hemes with axial His/OH and His/Tyr coordinations separated by the closest interheme distance of 14 Å. BthA has a similar structure and belongs to the same family of multiheme cytochrome peroxidases as MauG, which performs long-range oxidation of the partner protein methylamine dehydrogenase. Magnetic Mössbauer spectroscopy of the diferric state of BthA corroborates previous structural work identifying a high-spin (His/OH) peroxidatic heme and a low-spin (His/Tyr) electron transfer heme. Unlike MauG, addition of HO fully converts the diferric form of BthA to a stable 2e oxidized state, allowing a new assessment of this state. The peroxidatic heme is found to be oxidized to a canonical compound II, S = 1 oxoiron(IV) heme. In contrast, the electronic properties of the oxidized His/Tyr heme are puzzling. The isomer shift of the His/Tyr heme (0.17 mm/s) is close to that of the precursor S = 1/2 Fe heme (0.21 mm/s) which suggests oxidation of the Tyr. However, the spin-dipolar hyperfine coupling constants are found here to be the same as those for the ferryl peroxidatic heme, indicating that the His/Tyr heme is also a compound II, S = 1 Fe heme and ruling out oxidation of the Tyr. DFT calculations indicate that the unusually high isomer shift is not attributable to the rare axial His/Tyr heme coordination. The calculations are only compatible with spectroscopy for an unusually long Fe-O distance, which is presumably under the influence of the protein environment of the His/Tyr heme moiety in the HO oxidized state of the protein. The results offer new insights into how high valence intermediates can be tuned by the protein environment for performing long-range oxidation.
来自该微生物的BthA蛋白含有两个血红素，其轴向配体分别为His/OH和His/Tyr，两个血红素之间的最短距离为14 Å。BthA具有相似的结构，与MauG属于同一多血红素细胞色素过氧化物酶家族，MauG负责对伴侣蛋白甲胺脱氢酶进行远程氧化。对BthA的二价铁状态进行的磁性穆斯堡尔光谱证实了之前的结构研究结果，即鉴定出一个高自旋（His/OH）的过氧化物血红素和一个低自旋（His/Tyr）的电子转移血红素。与MauG不同，添加HO可使BthA的二价铁形式完全转化为稳定的2e氧化态，从而能够对该状态进行新的评估。发现过氧化物血红素被氧化为典型的化合物II，即S = 1的氧合铁（IV）血红素。相比之下，氧化后的His/Tyr血红素的电子性质令人困惑。His/Tyr血红素的同质异能位移（0.17 mm/s）与前体S = 1/2 Fe血红素的同质异能位移（0.21 mm/s）相近，这表明Tyr发生了氧化。然而，在此发现自旋 - 偶极超精细耦合常数与铁酰过氧化物血红素的相同，这表明His/Tyr血红素也是一种化合物II，即S = 1的Fe血红素，排除了Tyr的氧化。密度泛函理论计算表明，异常高的同质异能位移并非归因于罕见的轴向His/Tyr血红素配位。这些计算结果仅与异常长的Fe - O距离的光谱结果相符，这可能是由于在蛋白质的HO氧化态下，His/Tyr血红素部分的蛋白质环境的影响。这些结果为高价中间体如何通过蛋白质环境进行调节以实现远程氧化提供了新的见解。
