Meyer O, Gremer L, Ferner R, Ferner M, Dobbek H, Gnida M, Meyer-Klaucke W, Huber R
Lehrstuhl für Mikrobiologie, Universität Bayreuth, Germany.
Biol Chem. 2000 Sep-Oct;381(9-10):865-76. doi: 10.1515/BC.2000.108.
CO dehydrogenase (EC 1.2.99.2) catalyzes the oxidation of CO according to the following equation: CO + H2O-->CO2 + 2 e- + 2 H+. It is a selenium-containing molybdo-iron-sulfur-flavoenzyme, which has been crystallized and structurally characterized in its oxidized state from the aerobic CO utilizing bacteria Oligotropha carboxidovorans and Hydrogenophaga pseudoflava. Both CO dehydrogenase structures show only minor differences, and the enzymes are dimers of two heterotrimers. Each heterotrimer is composed of a molybdoprotein, a flavoprotein, and an iron-sulfur protein. CO oxidation takes place at the molybdoprotein which contains a 1:1 mononuclear complex of molybdopterin-cytosine dinucleotide and a Mo-ion, along with a catalytically essential S-selanylcysteine. The latter is appropriately positioned in the SeMo-active site by a unique VAYRCSFR active site loop. In H. pseudoflava the arginine preceeding the cysteine in the active site loop is modified to a Cgamma-hydroxy arginine residue which has no obvious function. The substituents in the first coordination sphere of the Mo-ion are the enedithiolate sulfur atoms of the molybdopterin-cytosine dinucleotide, two oxo- and a sulfido-group. Extended X-ray absorption fine structure spectroscopy (EXAFS), along with the crystal structure of CO dehydrogenase (23.2 U mg(-1)) at 1.85 A resolution, have identified a sulfur atom at 2.3 A from the Mo-ion. The sulfur reacts with cyanide yielding thiocyanate. The corresponding inactive desulfo-CO dehydrogenase shows a typical desulfo inhibited-type of Mo-electron paramagnetic resonance (EPR) spectrum. Structural changes at the SeMo-site during catalysis are suggested by the Mo to Se distance of 3.7 A and the Mo-S-Se angle of 113 degrees in the oxidized enzyme which increase to 4.1 A, and 121 degrees, respectively, in the reduced enzyme. The intramolecular electron transport chain in CO dehydrogenase involves the following prosthetic groups and minimal distances: CO-->[Mo of the molybdenum cofactor] - 14.6 A - [2Fe-2S]I - 12.4 A - [2Fe-2S]II - 8.7 A - [FAD].
一氧化碳脱氢酶（EC 1.2.99.2）根据以下方程式催化一氧化碳的氧化：CO + H₂O → CO₂ + 2e⁻ + 2H⁺。它是一种含硒的钼铁硫黄素酶，已从利用一氧化碳的需氧细菌嗜羧寡养单胞菌和假黄氢噬胞菌中结晶出来，并对其氧化态进行了结构表征。两种一氧化碳脱氢酶的结构仅显示出微小差异，且这些酶是由两个异源三聚体组成的二聚体。每个异源三聚体由一个钼蛋白、一个黄素蛋白和一个铁硫蛋白组成。一氧化碳的氧化发生在钼蛋白上，该钼蛋白含有一个钼蝶呤 - 胞嘧啶二核苷酸与一个钼离子的1:1单核配合物，以及一个催化必需的S - 硒代半胱氨酸。后者通过一个独特的VAYRCSFR活性位点环适当地定位在硒钼活性位点中。在假黄氢噬胞菌中，活性位点环中半胱氨酸之前的精氨酸被修饰为一个γ - 羟基精氨酸残基，其功能不明显。钼离子第一配位层中的取代基是钼蝶呤 - 胞嘧啶二核苷酸的烯二硫醇硫原子、两个氧代基团和一个硫代基团。扩展X射线吸收精细结构光谱（EXAFS）以及分辨率为1.85 Å的一氧化碳脱氢酶（23.2 U mg⁻¹）晶体结构，已确定在距钼离子2.3 Å处有一个硫原子。该硫与氰化物反应生成硫氰酸盐。相应的无活性脱硫一氧化碳脱氢酶显示出典型的脱硫抑制型钼电子顺磁共振（EPR）光谱。催化过程中硒钼位点的结构变化由氧化态酶中钼与硒的距离为3.7 Å以及钼 - 硫 - 硒角度为113°表明，在还原态酶中分别增加到4.1 Å和121°。一氧化碳脱氢酶中的分子内电子传递链涉及以下辅基和最小距离：CO → [钼辅因子的钼] - 14.6 Å - [2Fe - 2S]I - 12.4 Å - [2Fe - 2S]II - 8.7 Å - [FAD]。
