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首页> 外文期刊>Biochemistry >Stricture and Spectroscopy of the Periplasmic Cytochrome c Nitrite Reductase from Escherichia coli
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Stricture and Spectroscopy of the Periplasmic Cytochrome c Nitrite Reductase from Escherichia coli

机译：大肠杆菌周质细胞色素c亚硝酸盐还原酶的结构和光谱

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摘要

The crystal structure and spectroscopic properties of the periplasmic penta-heme cytochrome c nitrite reductase (NrfA) of Escherichia coli are presented. The structure is the first for a member of the NrfA subgroup that utilize a soluble penta-heme cytochrome, NrfB, as a redox partner. Comparison to the structures of Wolinella succinogenes NrfA and Sulfospirillum deleyianum NrfA, which accept electrons the structures of Wolinella succinogenes NrfA and Sulfospirillum deleyianum NrfA, which accept electrons from a membrane-anchored tetra-heme cytochrome (NrfH), reveals notable differences in the protein surface around heme 2, which may be the docking site for the redox partner. The structure shows that four of the NrfA hemes (hemes 2-5) have bis-histidine axial heme-Fe ligation. The catalytic heme-Fe(heme 1) has a lysine distal ligand and an oxygen atom proximal ligand. Analysis of NrfA in solution by magnetic circular dichroism (MCD) suggested that the oxygen ligand arose from water. Electron paramagnetic resonance (EPR) spectra were collected from electrochemically poised NrfA samples. Broad perpendicular mode singals at g approx 10.8 and 3.5, characteristic of weakly spin-coupled S = 5/2, S = 1/2 paramagnets, titrated with E_m = -107 mV. A possible origin for these are the active site Lys-OH_2 coordinated heme (heme 1) and a nearby bis-His coordinated heme (heme 3). A rhombic heme Fe(III) EPR signal at g_z = 2.91, g_y = 2.3, g_x = 1.5 titrated with E_m = -37 mV and is likely to arise from bis-His coordinated hemes (heme 2) in which the interplanar angle of the imidazole rings is 21.2 deg. The final two bis-His coordinated hemes (heme 4 and 5) have imidazole interplanar angles of 64.4 deg and 71.8 deg. Either, or both, of these hemes could give rise to a "Large g max" EPR signal at g_z = 3.17 that titrated at potentials between -250 and -400 mV. Previous spectroscopic studies studies on NrfA from a number of bacterial species are considered in the light of the structure-based spectro-potentiometric analysis presented for the E.coli NrfA.
机译：介绍了大肠埃希氏菌周质五血红素细胞色素c亚硝酸还原酶（NrfA）的晶体结构和光谱性质。该结构是利用可溶五血红素细胞色素NrfB作为氧化还原伴侣的NrfA亚组成员的第一个结构。与接受电子的Wolinella succinogenes NrfA和Sulfospirillum deleyianum NrfA的结构进行比较，揭示了接受Wolinella succinogenes NrfA和Sulfospirillum deleyianum NrfA的结构，这些结构接受膜锚定的四血红素细胞色素（NrfH）表面差异的电子在血红素2周围，这可能是氧化还原伙伴的对接站点。该结构表明，四个NrfA血红素（2-5 hemes）具有双组氨酸轴向血红素-Fe连接。催化血红素-Fe（血红素1）具有赖氨酸远端配体和氧原子近端配体。通过磁圆二色性（MCD）分析溶液中的NrfA，表明氧配体是从水中产生的。从电化学平衡的NrfA样品中收集电子顺磁共振（EPR）光谱。 g约为10.8和3.5的宽垂直模式信号，具有弱自旋耦合S = 5/2，S = 1/2顺磁体的特性，并用E_m = -107 mV进行了滴定。这些的可能来源是活性位点Lys-OH_2配合的血红素（血红素1）和附近的bis-His配合的血红素（血红素3）。菱形血红素Fe（III）EPR信号在g_z = 2.91，g_y = 2.3，g_x = 1.5且用E_m = -37 mV滴定时很可能是由bis-His配位的血红素（血红素2）引起的，其中咪唑环为21.2度。最后两个bis-His配位的血红素（血红素4和5）的咪唑平面间角为64.4度和71.8度。这些血红素中的一个或两个，都可能在g_z = 3.17时产生“大g max” EPR信号，该信号在-250至-400 mV的电势下滴定。根据针对大肠杆菌NrfA的基于结构的分光电位分析，考虑了以前对许多细菌物种进行NrfA的光谱研究。

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