Distinct metal-binding configurations in metallothionein.
Distinct metal-binding configurations in metallothionein.
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DOI：
10.1016/s0021-9258(18)89027-5
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发表时间：
1985-05
期刊：
影响因子：
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通讯作者：
K. Nielson;C L Atkin;D. R. Winge
中科院分区：
文献类型：
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作者：
K. Nielson;C L Atkin;D. R. Winge
在一项对各种金属与大鼠肝金属硫蛋白结合的化学计量学研究中，该蛋白似乎以两种不同的构型协调金属。至少有18种不同金属的离子被证明与蛋白质结合，这表明这种结合几乎没有特异性。大多数金属在7摩尔当量下发生饱和结合，形成m7 -金属硫蛋白。这些包括Bi（III）、Cd（II）、Co（II）、Hg（II）、In（III）、Ni（II）、Pb（II）、Sb（III）和Zn（II）。其他金属，包括Os(III), Pd(II), Pt(IV), Re(V), Rh（III）和Tl（III）给出了积极的结合指示，但化学计量学不清楚。Ag(I)和Cu(I)结合成m12 -金属硫蛋白簇。这种结合化学计量学是通过3种方式确定的：(a)通过确定铜和银滴定样品中的等当点，其中对蛋白质水解的抗性最大；(b)测定锌离子从锌-金属硫蛋白中完全置换的点；(c)直接结合研究。凝胶过滤回收的Ag重组蛋白平均Ag含量为11.5 g原子/mol蛋白质。Cu-蛋白的化学计量学类似于Zn -金属硫蛋白中的Zn被Cu(I)取代。用7 mol当量的Hg（II）置换Ag(I)或Cu(I)，使m12蛋白转化为m7蛋白。金属在m7 -金属硫蛋白2个结构域的分布是M4 α和M3 β，而在m12 -金属硫蛋白分子中的排列可能是M6 α和M6 β。我们提出金属硫蛋白通过桥接硫化物将Ag(I)和Cu(I)连接成一个三角形几何结构。这与m7蛋白的四面体结合几何形状形成对比。不同的结合构型可能导致M7-和m12蛋白的三级结构不同，这可能分别与锌金属硫蛋白和铜金属硫蛋白的代谢特异性有关。
In a study of the binding stoichiometry of various metals to rat liver metallothionein, the protein appears to coordinate metals in 2 distinct configurations. Ions of at least 18 different metals were shown to associate with the protein suggesting that there is little specificity in binding. Most metals exhibited saturation binding at 7 mol eq forming M7-metallothionein. These included Bi(III), Cd(II), Co(II), Hg(II), In(III), Ni(II), Pb(II), Sb(III), and Zn(II). Others metals including Os(III), Pd(II), Pt(IV), Re(V), Rh(III), and Tl(III) give a positive indication of binding, but stoichiometries were unclear. Ag(I) and Cu(I) bound in clusters as M12-metallothionein. This binding stoichiometry was determined in 3 ways: (a) by determining the equivalence point in Cu- and Ag-titrated samples where resistance to proteolysis is maximal; (b) by determining the point where Zn ions are completely displaced from Zn7-metallothionein; and (c) by direct binding studies. Ag-reconstituted protein, recovered from gel filtration, had an average Ag content of 11.5 g atoms/mol of protein. A similar stoichiometry for the Cu-protein resulted from displacement of Zn from Zn7-metallothionein by Cu(I). The M12-protein was converted to the M7-protein by displacement of Ag(I) or Cu(I) with 7 mol eq of Hg(II). Whereas the distribution of metals in the 2 domains of M7-metallothionein is M4 alpha and M3 beta, the arrangement in the M12-molecule is probably M6 alpha and M6 beta. We propose that metallothionein ligates Ag(I) and Cu(I) in a trigonal geometry by bridging thiolates. This is in contradistinction to a tetrahedral binding geometry in the M7-protein. Distinct binding configurations may result in different tertiary structures for M7- and M12-proteins which may relate to metabolic specificity of Zn-metallothionein and Cu-metallothionein, respectively.