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首页> 外文期刊>Biochemistry >Assignment of heme resonances and determination of the electronic structures of high- and low-spin nitrophorin 2 by (1)h and (13)c NMR spectroscopy: an explanation of the order of heme methyl resonances in high-spin ferriheme proteins.
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Assignment of heme resonances and determination of the electronic structures of high- and low-spin nitrophorin 2 by (1)h and (13)c NMR spectroscopy: an explanation of the order of heme methyl resonances in high-spin ferriheme proteins.

机译：通过（1）h和（13）c NMR光谱确定血红素共振并确定高旋和低旋硝化蛋白2的电子结构：高旋铁蛋白血红素甲基共振顺序的解释。

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摘要

The (1)H NMR resonances of the heme substituents of the low-spin Fe(III) form of nitrophorin 2, as its complexes with N-methylimidazole (NP2-NMeIm) and imidazole (NP2-ImH), have been assigned by a combination of (1)H homonuclear two-dimensional NMR techniques and (1)H-(13)C HMQC. Complete assignment of the proton and partial assignment of the (13)C resonances of the heme of these complexes has been achieved. Due to favorable rates of ligand exchange, it was also possible to assign part of the (1)H resonances of the high-spin heme via saturation transfer between high- and low-spin protein forms in a partially liganded NP2-NMeIm sample; additional resonances (vinyl and propionate) were assigned by NOESY techniques. The order of heme methyl resonances in the high-spin form of the protein over the temperature range of 10-37 degrees C is 8 = 5 > 1 > 3; the NMeIm complex has 5 > 1 > 3 > 8 as the order of heme methyl resonances at <30 degrees C, while above that temperature, the order is 5 > 3 > 1 > 8, due tocrossover of the closely spaced 3- and 1-methyl resonances of the low-spin complex at higher temperatures. This crossover defines the nodal plane of the heme orbital used for spin delocalization as being oriented 162 +/- 2 degrees clockwise from the heme N(II)-Fe-N(IV) axis for the heme in the B orientation. For the NP2-ImH complex, the order of heme methyl resonances is 3 > 5 > 1 > 8, which defines the orientation of the nodal plane of the heme orbital used for spin delocalization as being oriented approximately 150-155 degrees clockwise from the heme N(II)-Fe-N(IV) axis. In both low-spin complexes, the results are most consistent with the exogenous planar ligand controlling the orientation of the nodal plane of the heme orbital. In the high-spin form of NP2, the proximal histidine plane is shown to be oriented 135 degrees clockwise from the heme N(II)-Fe-N(IV) axis, again for the B heme orientation. A correlation between the order of heme methyl resonances in the high-spin form of NP2 and several other ferriheme proteins and an apparent 90 degrees shift in the nodal plane of the orbital involved in spin delocalization from that expected on the basis of the orientation of the axial histidine imidazole nodal plane have been explained in terms of bonding interactions between Fe(III), the axial histidine imidazole nitrogen, and the porphyrin pi orbitals of the high-spin protein.
机译：低旋转Fe（III）形式的氮荧光蛋白2（与N-甲基咪唑（NP2-NMeIm）和咪唑（NP2-ImH）的配合物）的血红素取代基的（1）H NMR共振由（1）H同核二维NMR技术与（1）H-（13）C HMQC的组合。这些复合物的质子的完全分配和血红素的（13）C共振的部分分配已实现。由于配体交换的速率较高，还可以通过部分配体的NP2-NMeIm样品中高纺丝和低纺丝蛋白形式之间的饱和转移来分配高纺丝血红素的部分（1）H共振;通过NOESY技术分配了其他共振（乙烯基和丙酸酯）。在10-37摄氏度的温度范围内，蛋白质的高纺丝形式血红素甲基共振的顺序为8 = 5> 1> 3; NMeIm络合物在<30摄氏度时具有5> 1> 3> 8的血红素甲基共振顺序，而在该温度以上，由于紧密排列的3-和1的交叉，该顺序为5> 3> 1> 8。低旋转复合物在较高温度下的-甲基共振。该分界线定义了用于自旋离域的血红素轨道的节平面，其相对于血红素在B方向上的血红素N（II）-Fe-N（IV）轴顺时针方向为162 +/- 2度。对于NP2-ImH络合物，血红素甲基共振的阶数为3> 5> 1> 8，这定义了用于自旋离域的血红素轨道的节面平面方向与血红素成顺时针方向大约150-155度N（II）-Fe-N（IV）轴。在两种低自旋复合物中，结果与控制血红素轨道的节平面取向的外源平面配体最一致。在NP2的高自旋形式中，近端组氨酸平面显示出与血红素N（II）-Fe-N（IV）轴顺时针方向135度定向，同样是B血红素定向。高旋转形式的NP2和其他几种亚铁血红素蛋白的血红素甲基共振顺序与自旋离域化所涉及的轨道节点平面上明显的90度位移之间的相关性与基于该位点的取向所预期的位置有关用Fe（III），轴向组氨酸咪唑氮和高自旋蛋白的卟啉pi轨道之间的键相互作用来解释轴向组氨酸咪唑的节点平面。

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