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首页> 外文期刊>Journal of Molecular Biology >THE STRUCTURE OF DEOXY- AND OXY-LEGHAEMOGLOBIN FROM LUPIN
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THE STRUCTURE OF DEOXY- AND OXY-LEGHAEMOGLOBIN FROM LUPIN

机译：亮氨酸中脱氧和氧-卵磷脂的结构

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The leghaemoglobins have oxygen affinities 11 to 24 times higher than that of sperm whale myoglobin, due mainly to higher rates of association. To find out why, we have determined the structures of deoxy- and oxy-leghaemoglobin II of the lupin at 1.7 Angstrom resolution. Results confirm the general features found in previous X-ray analyses of this protein. The unique feature that has now emerged is the rotational freedom of the proximal histidine. In deoxy-leghaemoglobin the imidazole oscillates between two alternative orientations, eclipsing either the lines N-1-N-3 or N-2-N-4 of the porphyrin; in oxy-leghaemoglobin it is fixed in a staggered orientation. The iron atom moves from a position 0.30 Angstrom from the plane of the pyrrole nitrogen atoms in deoxy- to a position in the plane in oxy-leghaemoglobin while the Fe-(N) bond distance remains constant at 2.02 Angstrom. The Fe-O-O angle is 152 degrees, as in human haemoglobin. The oxygen is hydrogen-bonded to the distal histidine at N-epsilon 2-O1 and N-epsilon 2-O2 distance of 2.95 Angstrom and 2.68 Angstrom, respectively. The porphyrin is ruffled equally in deoxy- and oxy-leghaemoglobins, due to rotations of the pyrrols about the N-Fe-N bonds, causing the methine bridges to deviate by up to 0.32 Angstrom from the mean porphyrin plane. The only feature capable of accounting for the high on-rate of the reaction with oxygen are the mobilities of the proximal histidine and distal histidine residues in deoxy-leghaemoglobin. The eclipsed positions of the proximal histidine in deoxy-leghaemoglobin maximize steric hindrance with the porphyrin nitrogen atoms and minimize pi-->p electron donation, while its staggered position in oxy-leghaemoglobin reverses both these effects. Together with the oscillation of the imidazole between the two orientations, these two factors may reduce the activation energy for the reaction of leghaemoglobin with oxygen. The distal histidine is in a fixed position in the haem pocket in the crystal, but must be swinging in and out of the pocket at a high rate in solution to allow the oxygen to enter. (C) 1995 Academic Press Limited [References: 44]
机译：血红蛋白的氧亲和力比抹香鲸的肌红蛋白高11到24倍，这主要是由于较高的结合率。为了找出原因，我们确定了羽扇豆的脱氧-和氧-升血红蛋白II的结构，分辨率为1.7埃。结果证实了该蛋白质在先前X射线分析中发现的一般特征。现在出现的独特特征是近端组氨酸的旋转自由度。在脱氧血红蛋白中，咪唑在两个不同的方向之间振荡，使卟啉的N-1-N-3或N-2-N-4线黯然失色;在氧-血红蛋白中，它以交错的方向固定。铁原子从脱氧的吡咯氮原子平面的0.30埃位置移动到氧-血红蛋白的平面内的位置，而Fe-（N）键的距离保持恒定在2.02埃。与人类血红蛋白一样，Fe-O-O角为152度。氧以2.95埃和2.68埃的N-ε2 -O 1和N-ε2 -O 2距离氢键合至远端组氨酸。由于吡咯围绕N-Fe-N键的旋转，卟啉在脱氧和含氧血红蛋白中均等地起伏，导致次甲基桥与平均卟啉平面相差最大0.32埃。能够说明与氧气的高反应速率的唯一特征是脱氧-豆血红蛋白中近端组氨酸和远端组氨酸残基的迁移率。脱氧-血红蛋白中近端组氨酸的偏光位置使卟啉氮原子的空间位阻最大化，并使pi-> p电子供体最小化，而氧-血红蛋白中的交错位置则逆转了这两种作用。连同咪唑在两个方向之间的振荡，这两个因素可能会降低豆血红蛋白与氧气反应的活化能。远端组氨酸在晶体的血红素袋中处于固定位置，但必须在溶液中以高速率在袋中摆动和摆动，以允许氧气进入。 （C）1995 Academic Press Limited [参考号：44]

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