Is apomyoglobin a molten globule? Structural characterization by NMR
Is apomyoglobin a molten globule? Structural characterization by NMR
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DOI：
10.1006/jmbi.1996.0596
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发表时间：
1996-11-08
影响因子：
5.6
通讯作者：
Wright, PE
中科院分区：
文献类型：
--
作者：
Eliezer, D;Wright, PE
多维异核核磁共振波谱已被用来获得天然状态(pH 6.1)下同位素标记的重组抹香鲸去肌红蛋白的结构信息。对蛋白质中大部分残基的主链共振((HN)-H-1，N-15和C-13(α))进行了指认。观察到的化学位移表明的二级结构与所有指定区的一氧化碳-全息肌红蛋白中的二级结构几乎相同。此外，这两种蛋白质的化学位移本身高度相似。这表明去肌红蛋白多肽链的大部分采用了与全肌红蛋白非常相似的结构。然而，由于构象波动，来自载脂蛋白连续区域的骨架共振，对应于EF环、F螺旋、FG环和G螺旋的开始，被拓宽到无法检测到的范围。我们认为，该区域的多肽在全蛋白样构象和一个或多个未折叠或部分折叠状态之间进行交换。这样的模型可以解释当前的核磁共振数据，质谱学观察到的电荷态分布，以及诱变的影响。去肌红蛋白具有天然球状蛋白的许多特征，并不符合经典的熔化球状蛋白的描述。
Multi-dimensional heteronuclear NMR spectroscopy has been used to obtain structural information on isotopically labeled recombinant sperm whale apomyoglobin in the native state at pH 6.1. Assignments for backbone resonances ((HN)-H-1, N-15, and C-13(alpha)) have been made for a large fraction of the residues in the protein. The secondary structure indicated by the observed chemical shifts is nearly identical to that found in carbonmonoxy-holomyoglobin in all assigned regions. In addition the chemical shifts themselves are highly similar in both proteins. This suggests that the majority of the apomyoglobin polypeptide chain adopts a well defined structure which is very similar to that of holomyoglobin. However, backbone resonances from a contiguous region of the apoprotein, corresponding to the EF loop, the F helix, the FG loop, and the beginning of the G helix, are broadened beyond detection due to conformational fluctuations. We propose that the polypeptide in this region exchanges between a holoprotein-like conformation and one or more unfolded or partially folded states. Such a model can explain the current NMR data, the charge state distributions observed by mass spectrometry, and the effects of mutagenesis. Apomyoglobin possesses many of the characteristics of a native, globular protein and does not adhere to the classical description of a molten globule.