Ultrahigh resolution structures of nitrophorin 4: Heme distortion in ferrous CO and NO complexes
Ultrahigh resolution structures of nitrophorin 4: Heme distortion in ferrous CO and NO complexes
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DOI：
10.1021/bi0506573
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发表时间：
2005-09-27
期刊：
影响因子：
2.9
通讯作者：
Montfort, WR
中科院分区：
文献类型：
--
作者：
Maes, EM;Roberts, SA;Montfort, WR
Nitrophorin 4（NP 4）是一种来自吸血昆虫Rhodnius prolixus的一氧化氮（NO）转运蛋白，利用铁（Fe 3+）血红素将NO输送到受害者。NO与NP 4的结合诱导了大的构象变化和远端口袋的完全去溶剂化。血红素是显着的非平面，显示一个褶皱变形假定有助于稳定的三价铁。在这里，我们报告的铁（Fe 2+）配合物的NP 4与NO，CO，和H2O形成后，化学还原的蛋白质和这些复合物的特征吸收光谱，闪光光解，和超高分辨率晶体学（分辨率从0.9到1.08埃不等）。的吸收光谱，无论是在溶液中和晶体中，是典型的六配位亚铁配合物。关闭和去溶剂化的远端口袋发生后，结合CO或NO的铁，无论血红素的氧化态，确认的构象变化是由远端配体极性驱动。亚铁血红素的褶皱程度与配体的性质和铁的氧化态有关，其顺序为：（Fe ~（3+）-NO >（Fe ~（2+））-NO>（Fe ~（2+））-CO >（Fe ~（3+）-H_2O>（Fe ~（2+）-H_2O。亚铁配位几何形状与预期一致，除了近端组氨酸键，其比模型化合物中通常发现的短。这些数据是一致的血红素皱褶和协调的几何结构，以稳定铁态的nitrophorins，其生理功能的要求。血红素扭曲和NO弯曲血红素蛋白功能的可能作用进行了讨论。
Nitrophorin 4 (NP4), a nitric oxide (NO)-transport protein from the blood-sucking insect Rhodnius prolixus, uses a ferric (Fe3+) heme to deliver NO to its victims. NO binding to NP4 induces a large conformational change and complete desolvation of the distal pocket. The heme is markedly nonplanar, displaying a ruffling distortion postulated to contribute to stabilization of the ferric iron. Here, we report the ferrous (Fe2+) complexes of NP4 with NO, CO, and H2O formed after chemical reduction of the protein and the characterization of these complexes by absorption spectroscopy, flash photolysis, and ultrahigh-resolution crystallography (resolutions vary from 0.9 to 1.08 angstrom). The absorption spectra, both in solution and in the crystal, are typical for six-coordinated ferrous complexes. Closure and desolvation of the distal pocket occurs upon binding CO or NO to the iron regardless of the heme oxidation state, confirming that the conformational change is driven by distal ligand polarity. The degree of heme ruffling is coupled to the nature of the ligand and the iron oxidation state in the following order: (Fe3+)-NO > (Fe2+)-NO > (Fe2+)-CO > (Fe3+)-H2O > (Fe2+)-H2O. The ferrous coordination geometry is as expected, except for the proximal histidine bond, which is shorter than typically found in model compounds. These data are consistent with heme ruffling and coordination geometry serving to stabilize the ferric state of the nitrophorins, a requirement for their physiological function. Possible roles for heme distortion and NO bending in heme protein function are discussed.