GEOMETRY OF THE SOLUBLE METHANE MONOOXYGENASE CATALYTIC DIIRON CENTER IN 2 OXIDATION-STATES
GEOMETRY OF THE SOLUBLE METHANE MONOOXYGENASE CATALYTIC DIIRON CENTER IN 2 OXIDATION-STATES
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DOI：
10.1016/1074-5521(95)90222-8
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发表时间：
1995-06-01
影响因子：
--
通讯作者：
LIPPARD, SJ
中科院分区：
文献类型：
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作者：
ROSENZWEIG, AC;NORDLUND, P;LIPPARD, SJ
背景：可溶性甲烷单加氧酶(SMMO)的羟基酶组分含有一个双核铁中心，负责将甲烷氧化成甲醇。在分离时，中心处于氧化的二铁(III)状态。甲氧基球囊菌(Bath)氧化羟基酶H-OX的2.2Angstrom分辨X射线结构是在4℃下测定的。在这种结构中，两个铁原子由谷氨酸、氢氧离子和乙酸根离子桥联，并与两个组氨酸残基、三个谷氨酸残基和一个水分子配位。结果：从甲基球囊菌(Bath)中分离得到的mMMO羟基酶的1.7Angstrom分辨晶体结构，无论是氧化铁(III)、H-OX，还是经二亚硫酸盐处理、还原的二铁(II)、H-红、在-160℃下测定了氧化态。H-ox中二铁中心的结构与以前报道的2.2埃分辨率和4℃下的结构不同。虽然保留了氢氧化桥，但指定为乙酸酯的双齿桥联配体被弱配位的单原子水桥取代。在得到的四元Fe(OH)Fe(OH2)环中，Fe(OH)Fe(OH2)环上的Fe(OH)Fe(OH2)…Fe距离从3.4埃缩短到3.1埃。在H-red的原形A中，氢氧桥被Glu243的氧原子取代，Glu243经历了羧酸从H-ox中的末端单齿结合模式转变为羧酸盐既是单原子桥联又是双齿螯合的模式。因此，我们得出结论，该中心已被还原为二铁(II)氧化态。在所得到的结构中，两个铁原子都与五个配体配位，而与第六个水分子配位较弱。H-RED原核B中的双铁中心与H-OX中的双铁中心组成相同。在氧化和还原结构中，双铁中心通过外源物种氢键连接到活性中心空穴中的Thr213。结论：H-OX中的双铁中心可以改变其外源配体的配位和几何构型，这一性质在sMMO的催化循环中可能是重要的。在H-红中，羧酸盐发生移动，挤出氢氧离子并打开配位与O-2反应，形成二铁(III)过氧基中间体H-过氧基。Thr213残基可能具有催化作用。
Background: The hydroxylase component of soluble methane monooxygenase (sMMO) contains a dinuclear iron center responsible for the oxidation of methane to methanol. As isolated, the center is in the oxidized, diiron(III) state. The 2.2 Angstrom resolution X-ray structure of the oxidized hydroxylase, H-OX, from Methylococcus capsulatus (Bath) was previously determined at 4 degrees C. In this structure the two iron atoms are bridged by a glutamate, a hydroxide ion, and an acetate ion, and additionally coordinated to two His residues, three Glu residues, and a water molecule.Results: The 1.7 Angstrom resolution crystal structures of the sMMO hydroxylase from Methylococcus capsulatus (Bath) in both its oxidized diiron(III), H-OX, and dithionite-treated, reduced diiron(II), H-red, oxidation states were determined at -160 degrees C. The structure of the diiron center in H-OX differs from that previously reported at 2.2 Angstrom resolution and 4 degrees C. Although the hydroxide bridge is retained, the bidentate, bridging ligand assigned as acetate is replaced by a weakly coordinating monoatomic water bridge. In the resulting four-membered Fe(OH)Fe(OH2) ring, the Fe ... Fe distance is shortened from 3.4 Angstrom to 3.1 Angstrom. In protomer A of H-red, the hydroxide bridge is displaced by an oxygen atom of Glu243, which undergoes a carboxylate shift from its terminal monodentate binding mode in H-OX to a mode in which the carboxylate is both monoatomic bridging and bidentate chelating. We therefore conclude that the center has been reduced to the diiron(II) oxidation state. Both iron atoms are coordinated to five ligands and weakly to a sixth water molecule in the resulting structure. The diiron center in protomer B of H-red has the same composition as those in H-OX. In both the oxidized and reduced structures, the diiron core is connected through hydrogen bonds involving exogenous species to Thr213 in the active site cavity.Conclusions: The diiron center in H-OX can change its exogenous ligand coordination and geometry, a property that could be important in the catalytic cycle of sMMO. In H-red, a carboxylate shift occurs, extruding hydroxide ion and opening coordination sites for reaction with O-2 to form the diiron(III) peroxo intermediate, H-peroxo. Residue Thr213 may function in catalysis.