Evolution of metal(loid) binding sites in transcriptional regulators
Evolution of metal(loid) binding sites in transcriptional regulators
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DOI：
10.1074/jbc.m803209200
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发表时间：
2008-09-12
影响因子：
4.8
通讯作者：
Rosen, Barry P.
中科院分区：
文献类型：
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作者：
Ordonez, Efren;Thiyagarajan, Saravanamuthu;Rosen, Barry P.
重金属和类金属抗性基因的表达受有毒离子本身的转录调控。小金属调节蛋白ArsR/SmtB家族的成员对过渡金属、重金属和类金属有反应，包括As（III）、Sb（III）、Cd（II）、Pb（II）、Zn（II）、Co（II）和Ni（II）。这些同源二聚体阻遏物在不存在诱导金属（类）离子的情况下与DNA结合，并且在结合诱导物时与DNA解离。调节位点通常是由半胱氨酸硫醇盐组成的三配位或四配位金属结合位点。令人惊讶的是，在两个不同的As（III）-响应监管机构，类金属结合位点是在不同的位置在阻遏物，和Cd（II）的结合位点是在两个不同的位置在两个Cd（II）-响应监管机构。我们推测，ArsR/SmtB阻遏物有一个共同的骨架结构，即有翼螺旋DNA结合蛋白，但在诱导剂结合位点的位置有相当大的可塑性。在这里，我们表明，作为（III）的家庭成员，CgArsR 1谷氨酸棒杆菌，结合作为（III）的半胱氨酸三联体组成的半胱氨酸（15），半胱氨酸（16），半胱氨酸（55）。该结合位点显然与其他特征性ArsR/SmtB家族成员的结合位点无关。这与我们的假设一致，即DNA结合蛋白中的金属（类金属）结合位点在持续的环境压力下收敛地进化。
Expression of the genes for resistance to heavy metals and metalloids is transcriptionally regulated by the toxic ions themselves. Members of the ArsR/SmtB family of small metalloregulatory proteins respond to transition metals, heavy metals, and metalloids, including As(III), Sb(III), Cd(II), Pb(II), Zn(II), Co(II), and Ni(II). These homodimeric repressors bind to DNA in the absence of inducing metal(loid) ion and dissociate from the DNA when inducer is bound. The regulatory sites are often three- or four-coordinate metal binding sites composed of cysteine thiolates. Surprisingly, in two different As(III)-responsive regulators, the metalloid binding sites were in different locations in the repressor, and the Cd(II) binding sites were in two different locations in two Cd(II)-responsive regulators. We hypothesize that ArsR/SmtB repressors have a common backbone structure, that of a winged helix DNA-binding protein, but have considerable plasticity in the location of inducer binding sites. Here we show that an As(III)-responsive member of the family, CgArsR1 from Corynebacterium glutamicum, binds As(III) to a cysteine triad composed of Cys(15), Cys(16), and Cys(55). This binding site is clearly unrelated to the binding sites of other characterized ArsR/SmtB family members. This is consistent with our hypothesis that metal(loid) binding sites in DNA binding proteins evolve convergently in response to persistent environmental pressures.