Maiti Biplab K, Maia Luisa B, Pauleta Sofia R, Moura Isabel, Moura José J G
UCIBIO, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa , 2829-516 Caparica, Portugal.
Inorg Chem. 2017 Feb 20;56(4):2210-2220. doi: 10.1021/acs.inorgchem.6b02906. Epub 2017 Jan 27.
The Orange Protein (ORP) is a small bacterial protein, of unknown function, that harbors a unique molybdenum/copper (Mo/Cu) heterometallic cluster, [SMoSCuSMoS], noncovalently bound. The apo-ORP is able to promote the formation and stabilization of this cluster, using Cu- and MoS salts as starting metallic reagents, to yield a Mo/Cu-ORP that is virtually identical to the native ORP. In this work, we explored the ORP capability of promoting protein-assisted synthesis to prepare novel protein derivatives harboring molybdenum heterometallic clusters containing iron, cobalt, nickel, or cadmium in place of the "central" copper (Mo/Fe-ORP, Mo/Co-ORP, Mo/Ni-ORP, or Mo/Cd-ORP). For that, the previously described protein-assisted synthesis protocol was extended to other metals and the Mo/M-ORP derivatives (M = Cu, Fe, Co, Ni, or Cd) were spectroscopically (UV-visible and electron paramagnetic resonance (EPR)) characterized. The Mo/Cu-ORP and Mo/Cd-ORP derivatives are stable under oxic conditions, while the Mo/Fe-ORP, Mo/Co-ORP, and Mo/Ni-ORP derivatives are dioxygen-sensitive and stable only under anoxic conditions. The metal and protein quantification shows the formation of 2Mo:1M:1ORP derivatives, and the visible spectra suggest that the expected {SMoSMSMoS} complexes are formed. The Mo/Cu-ORP, Mo/Co-ORP, and Mo/Cd-ORP are EPR-silent. The Mo/Fe-ORP derivative shows an EPR S = / signal (E/D ≈ 0.27, g ≈ 5.3, 2.5, and 1.7 for the lower M= ±/ doublet, and g ≈ 5.7 and 1.7 (1.3 predicted) for the upper M = ±/ doublet), consistent with the presence of either one S = / Fe antiferromagnetically coupled to two S = / Mo or one S = / Fe and two S = 0 Mo ions, in both cases in a tetrahedral geometry. The Mo/Ni-ORP shows an EPR axial S = / signal consistent with either one S = / Ni and two S = 0 Mo or one S = / Ni antiferromagnetically coupled to two S = / Mo ions, in both cases in a square-planar geometry. The Mo/Cu-ORP and Mo/Cd-ORP are described as {Mo-Cu-Mo} and {Mo-Cd-Mo}, respectively, while the other derivatives are suggested to exist in at least two possible electronic structures, {Mo-M-Mo} ↔ {Mo-M-Mo}.
橙色蛋白（ORP）是一种功能未知的小型细菌蛋白，它含有一个独特的钼/铜（Mo/Cu）异金属簇[SMoSCuSMoS]，该簇以非共价键结合。脱辅基ORP能够利用铜盐和钼酸盐作为起始金属试剂促进该簇的形成和稳定，从而产生与天然ORP几乎相同的Mo/Cu-ORP。在这项工作中，我们探索了ORP促进蛋白质辅助合成的能力，以制备含有铁、钴、镍或镉取代“中心”铜的钼异金属簇的新型蛋白质衍生物（Mo/Fe-ORP、Mo/Co-ORP、Mo/Ni-ORP或Mo/Cd-ORP）。为此，将先前描述的蛋白质辅助合成方案扩展到其他金属，并对Mo/M-ORP衍生物（M = Cu、Fe、Co、Ni或Cd）进行了光谱表征（紫外可见光谱和电子顺磁共振（EPR））。Mo/Cu-ORP和Mo/Cd-ORP衍生物在有氧条件下稳定，而Mo/Fe-ORP、Mo/Co-ORP和Mo/Ni-ORP衍生物对氧气敏感，仅在无氧条件下稳定。金属和蛋白质定量分析表明形成了2Mo:1M:1ORP衍生物，可见光谱表明形成了预期的{SMoSMSMoS}配合物。Mo/Cu-ORP、Mo/Co-ORP和Mo/Cd-ORP的EPR信号为零。Mo/Fe-ORP衍生物显示出EPR S = 1/2信号（对于较低的M = ±1/2双峰，E/D ≈ 0.27，g ≈ 5.3、2.5和1.7；对于较高的M = ±1/2双峰，g ≈ 5.7和1.7（预测值为1.3）），这与一个S = 1/2的铁与两个S = 1/2的钼反铁磁耦合，或者一个S = 1/2的铁和两个S = 0的钼离子的存在一致，在这两种情况下均为四面体几何结构。Mo/Ni-ORP显示出EPR轴向S = 1/2信号，这与一个S = 1/2的镍和两个S = 0的钼，或者一个S = 1/2的镍与两个S = 1/2的钼离子反铁磁耦合一致，在这两种情况下均为平面正方形几何结构。Mo/Cu-ORP和Mo/Cd-ORP分别被描述为{Mo-Cu-Mo}和{Mo-Cd-Mo}，而其他衍生物被认为至少存在两种可能的电子结构，{Mo-M-Mo} ↔ {Mo-M-Mo}。
