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首页> 外文期刊>Journal of Molecular Biology >STRUCTURE AND OXYGEN AFFINITY OF CRYSTALLINE DESARG141-ALPHA HUMAN HEMOGLOBIN A IN THE T STATE
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STRUCTURE AND OXYGEN AFFINITY OF CRYSTALLINE DESARG141-ALPHA HUMAN HEMOGLOBIN A IN THE T STATE

机译：T态晶体DESARG141-α人血红蛋白A的结构和氧亲和力

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摘要

The correlation of a protein structure determined crystallographically to its functional properties determined in solution can be an extremely complex problem due to potential differences of protein conformational flexibility in the two physical states. A more direct approach to the correlation of structure with function is to examine both the structure and the function of a protein in the same crystalline environment. In this paper, the structural and functional properties of T state desArg hemoglobin (human hemoglobin modified by removal of the a-chain COOH-terminal residue, Arg141 alpha) have been studied in the same crystal form by high resolution X-ray diffraction methods and by polarized absorption microspectrophotometry Specifically, the crystal structure of deoxygenated desArg human hemoglobin has been refined at a 2.1 Angstrom resolution using crystals grown at low salt concentration from solutions of polyethylene glycol. The loss of Arg141 alpha and all of the salt bridges in which it participates is associated with subtle structural perturbations of the a-chains which include an increase in the conformational flexibility of both the NH2 and COOH-terminal peptides. Although the heme pockets appear unchanged and even the side-chain of Tyr140 is oriented nearly as in HbA, the functional characterization by microspectrophotometric measurements indicates that crystals of desArg hemoglobin bind oxygen with an affinity which is roughly 15-fold greater than that of crystals of human hemoglobin A. There is no alkaline Bohr effect or effect of chloride ions, but an acid Bohr effect is observed. The oxygen affinities measured along two principal axes of the crystals differ by 25%, indicating heterogeneity in the affinities of the oxygen binding sites. This finding and the measured Hill coefficient of unity suggest significant cooperativity in the binding of oxygen in these crystals. The origins of the observed heterogeneity and the implied cooperativity are unknown. [References: 40]
机译：晶体学上确定的蛋白质结构与其在溶液中确定的功能性质的相关性可能是一个极其复杂的问题，这是由于两种物理状态下蛋白质构象柔韧性的潜在差异。结构与功能相关性的更直接方法是在相同的结晶环境中检查蛋白质的结构和功能。在本文中，通过高分辨率X射线衍射方法研究了T形desArg血红蛋白（通过去除a链COOH末端残基修饰的人血红蛋白Arg141α）的结构和功能特性，并且通过偏振吸收分光光度法特别地，使用从聚乙二醇溶液中以低盐浓度生长的晶体，以2.1埃的分辨率精制了脱氧的desArg人血红蛋白的晶体结构。 Arg141α及其参与的所有盐桥的缺失与a链的细微结构扰动有关，其中包括NH2和COOH末端肽的构象柔韧性的增加。尽管血红素口袋看起来没有变化，甚至Tyr140的侧链也几乎与HbA一样取向，但通过显微分光光度法测量的功能表征表明，desArg血红蛋白的晶体结合氧的亲和力比HgA晶体的亲和力大15倍。人血红蛋白A。没有碱性玻尔效应或氯离子效应，但观察到酸性玻尔效应。沿晶体的两个主轴测得的氧亲和力相差25％，表明氧结合位点的亲和力不均匀。这一发现和测得的希尔单位系数表明在这些晶体中氧的结合中具有显着的协同作用。所观察到的异质性和隐含的合作性的起源是未知的。 [参考：40]

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