NMR structural studies reveal a novel protein fold for MerB, the organomercurial lyase involved in the bacterial mercury resistance system
NMR structural studies reveal a novel protein fold for MerB, the organomercurial lyase involved in the bacterial mercury resistance system
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DOI：
10.1021/bi049669z
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发表时间：
2004-07-06
期刊：
影响因子：
2.9
通讯作者：
Omichinski, JG
中科院分区：
文献类型：
--
作者：
Di Lello, P;Benison, GC;Omichinski, JG
抗汞细菌已经开发出一种由两种酶（MerA和MerB）组成的系统，这使得它们能够有效地对离子和有机汞化合物进行解毒。有机汞裂解酶（MerB）催化碳汞键的质子分解，导致离子汞和还原烃的形成。离子汞[Hg（II）]随后被特定的汞还原酶（MerA）还原为反应性较低的元素汞[Hg（0）]。为了更好地了解MerB独特的酶活性，我们使用核磁共振（NMR）光谱来确定游离酶的结构。MerB的特点是由一个新的蛋白质折叠组成的三个非相互作用的反平行β-片层包围六个α-螺旋。通过比较游离MerB和MerB/Hg/DTT复合物的NMR数据，我们确定了一组可能定义Hg/DTT结合位点的残基。这些残基聚集在两个半胱氨酸（C-96和C-159）周围，这两个半胱氨酸对MerB的催化活性至关重要。结构的详细分析表明，存在一个广泛的疏水性沟槽相邻的汞/DTT结合位点。这种广泛的疏水性凹槽具有与多种底物的烃部分相互作用的潜力，并且可以解释MerB的广泛底物特异性。
Mercury resistant bacteria have developed a system of two enzymes (MerA and MerB), which allows them to efficiently detoxify both ionic and organomercurial compounds. The organomercurial lyase (MerB) catalyzes the protonolysis of the carbon-mercury bond resulting in the formation of ionic mercury and a reduced hydrocarbon. The ionic mercury [Hg(II)] is subsequently reduced to the less reactive elemental mercury [Hg(0)] by a specific mercuric reductase (MerA). To better understand MerB's unique enzymatic activity, we used nuclear magnetic resonance (NMR) spectroscopy to determine the structure of the free enzyme. MerB is characterized by a novel protein fold consisting of three noninteracting antiparallel beta-sheets surrounded by six alpha-helices. By comparing the NMR data of free MerB and the MerB/Hg/DTT complex, we identified a set of residues that likely define a Hg/DTT binding site. These residues cluster around two cysteines (C-96 and C-159) that are crucial to MerB's catalytic activity. A detailed analysis of the structure revealed the presence of an extensive hydrophobic groove adjacent to this Hg/DTT binding site. This extensive hydrophobic groove has the potential to interact with the hydrocarbon moiety of a wide variety of substrates and may explain the broad substrate specificity of MerB.