Determination of the secondary structure and conformation of puroindolines by infrared and Raman spectroscopy
Determination of the secondary structure and conformation of puroindolines by infrared and Raman spectroscopy
复制标题
DOI：
10.1021/bi960869n
复制
发表时间：
1996-10-01
期刊：
影响因子：
2.9
通讯作者：
Pezolet, M
中科院分区：
文献类型：
--
作者：
Bihan, TL;Blochet, JE;Pezolet, M
首次用红外光谱和拉曼光谱研究了小麦幼苗中的两种碱性脂结合蛋白puroindoline-a和puroindoline-b的构象。红外光谱结果表明，在pH为7时，吡喃吲哚碱-a和-b具有相似的二级结构，分别由约30%的α-螺旋、30%的β-折叠和40%的无序结构组成。两种葡吲哚的构象都显著地依赖于pH。二硫键的减少导致了吡喃吲哚类化合物在水中的溶解度降低，β-折叠含量增加了约15%，但α-螺旋的含量有所下降。拉曼光谱证实了两个吡喃吲哚之间的结构相似，但侧链环境的差异很小。所有的二硫键都是以guche-guche-guche构象存在的，并且在两个puroindoline中存在的唯一的酪氨酸残基是与水氢键的。在H2O和D2O介质中都记录了拉曼光谱，从而提供了关于某些残留物对水的可及性的额外信息。我们还观察到，在酸性和高离子强度条件下，puroindoline-a倾向于形成一些聚集体。近紫外圆二色谱测量表明，富含色氨酸的结构域参与了这种聚集体的形成。最后，在红外光谱和序列构象分析的基础上，我们提出了两个吡喃吲哚类化合物的二级结构归属。结果表明，puroindolines与植物非特异性脂转移蛋白和某些淀粉酶-蛋白酶抑制剂具有相似的折叠模式。这些蛋白质可以形成一个同质的植物蛋白结构家族，参与抵御病原体的攻击，这些病原体可能来自共同的螺旋状蛋白质祖先。
The conformation of puroindoline-a and -b, two basic lipid-binding proteins isolated from wheat seedlings, has been studied fur the first time by infrared and Raman spectroscopy. The infrared results show that puroindoline-a and -b have similar secondary structure composed of approximately 30% alpha-helices, 30% beta-sheets, and 40% unordered structure at pH 7. The conformation of both puroindolines is significantly pH-dependent. The reduction of the disulfide bridges leads to a decrease of the solubility of puroindolines in water and to an increase of the beta-sheet content by about 15% at the expense of the alpha-helix content. Raman spectroscopy confirms the structure similarity between the two puroindolines with little differences in the side chains' environment. All the disulfide bridges are in a gauche-gauche-gauche conformation, and the unique tyrosine residue present in both puroindolines is hydrogen-bonded to water. Raman spectra have been recorded in both H2O and D2O media, thus providing additional information concerning the accessibility of certain residues to water. We have also observed that puroindoline-a tends to form some aggregates under acidic and high ionic strength conditions. Near-ultraviolet circular dichroism measurements suggest that the tryptophan-rich domain is involved in this aggregate formation. Finally, on the basis of a combined infrared and sequence conformational analysis, we propose a secondary structure assignment for both puroindolines. The results show that puroindolines exhibit a similar folding pattern with plant nonspecific lipid-transfer protein and some amylase-protease inhibitors. These proteins could form a homogeneous structural family of plant proteins involved in the defense against pathogens that are probably derived from a common ''helicoidal'' protein ancestor.