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首页> 外文期刊>Biochemistry >Structural characterization of the apo form of a calcium binding protein from Entamoeba histolytica by hydrogen exchange and its folding to the holo state
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Structural characterization of the apo form of a calcium binding protein from Entamoeba histolytica by hydrogen exchange and its folding to the holo state

机译：通过解氢和折叠成完整状态来表征组织解脂变形杆菌的钙结合蛋白的载脂蛋白形式的结构特征

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摘要

One of the calcium binding proteins from Entamoeba histolytica (EhCaBP) is a 134 amino acid residue long (M-r similar to 14.9 kDa) double domain EF-hand protein containing four Ca2+ binding sites. CD and NMR studies reveal that the Ca2+-free form (apo-EhCaBP) exists in a partially collapsed form compared to the Ca2+-bound (holo) form, which has an ordered structure (PDB ID 1JFK). Deuterium exchange studies on the partially structured apo-EhCaBP reveal that the C-terminal domain is better structured than the N-terminal domain. The protein can be reversibly folded and unfolded upon addition of Ca2+ and EGTA, respectively. Titration shows a slow initial folding of the apo form with increasing Ca2+ concentration, followed by a highly cooperative folding to its final state at a certain threshold of Ca2+. Ca2+ and the EGTA titration taken together show that site 11 in the N-terminal domain has the highest affinity for Ca2+ contrary to earlier studies. Further, this study has thrown light on the relative Ca2+ binding affinity and specificity of each site in the intact protein. A structural model for the partially collapsed form of apo-EhCaBP and its equilibrium folding to its completely folded holo state has been suggested. Large conformational changes seen in transforming from the apo to holo form of EhCaBP suggest that this protein should be functioning as a sensor protein and might have a significant role in host-parasite recognition.
机译：来自解脂变形虫的钙结合蛋白（EhCaBP）之一是具有四个Ca 2+结合位点的134个氨基酸残基长（M-r类似于14.9kDa）双结构域EF-手蛋白。 CD和NMR研究表明，与具有有序结构（PDB ID 1JFK）的Ca2 +结合（全）形式相比，无Ca2 +形式（apo-EhCaBP）以部分折叠的形式存在。对部分结构的apo-EhCaBP进行氘交换研究表明，C末端结构域比N末端结构域结构更好。分别添加Ca2 +和EGTA后，蛋白质可以可逆地折叠和解折叠。滴定表明随着Ca2 +浓度的增加，载脂蛋白形式的初始折叠缓慢，随后在一定的Ca2 +阈值下高度协作地折叠至其最终状态。与早期的研究相反，Ca2 +和EGTA滴定一起显示N末端域中的位点11对Ca2 +具有最高的亲和力。此外，这项研究阐明了完整蛋白质中每个位点的相对Ca2 +结合亲和力和特异性。已经提出了apo-EhCaBP的部分折叠形式及其平衡折叠至完全折叠的整体状态的结构模型。从载脂蛋白转变为全能型EhCaBP时看到的大构象变化表明，该蛋白应起传感蛋白的作用，并可能在宿主寄生虫识别中起重要作用。

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