Ponnuswamy P K, Selvaraj S
Department of Physics, Bharathidasan University, Tamil Nadu, India.
Protein Seq Data Anal. 1992;5(1):47-56.
The presence of 22-residue repeats, each with a preferential potential to form an amphipathic alpha-helix, is a unique feature of the plasma apolipoproteins. There are 27 such repeats in the three human apolipoproteins A-I, A-IV, and E. The extent of similarities and differences among these repeats have been estimated by computing correlation coefficients, Dayhoff scores, secondary structure difference profiles, and discrete Fourier transforms. The results reveal that there is a high level of similarity among the repeats of apo A-IV, and a low level of similarity in the repeats of apo E. Within each protein, similarity among some specified repeat pairs is distinctively higher than the others. A high order of similarity is also found among certain segments of each protein with those in the other two. The repeats prefer a mostly alpha-helical structure that is amphipathic in nature. Among the repeats of the three proteins, those of apo E show a high level of divergence among themselves. A consensus alignment of the residues of the 27 repeats into a hydrophobic versus hydrophilic pattern brings to focus the possible specific structure-stabilizing factors, such as the leucine zipper and the salt bridge. The recently reported crystal structures of the human apolipoprotein E and locust apolipophorin-III support many of the predictions made in this study.
存在22个残基的重复序列，每个重复序列都具有形成两亲性α-螺旋的优先潜力，这是血浆载脂蛋白的独特特征。在人类载脂蛋白A-I、A-IV和E中存在27个这样的重复序列。通过计算相关系数、Dayhoff分数、二级结构差异图谱和离散傅里叶变换，估计了这些重复序列之间的相似性和差异程度。结果表明，载脂蛋白A-IV的重复序列之间具有高度相似性，而载脂蛋白E的重复序列之间相似性较低。在每种蛋白质中，某些特定重复序列对之间的相似性明显高于其他序列对。在每种蛋白质的某些片段与其他两种蛋白质的相应片段之间也发现了高度的相似性。这些重复序列倾向于形成主要为两亲性的α-螺旋结构。在这三种蛋白质的重复序列中，载脂蛋白E的重复序列之间表现出高度的差异。将27个重复序列的残基按照疏水与亲水模式进行一致排列，突出了可能的特定结构稳定因素，如亮氨酸拉链和盐桥。最近报道的人类载脂蛋白E和蝗虫载脂蛋白III的晶体结构支持了本研究中的许多预测。
