Laurents D V, Subbiah S, Levitt M
Beckman Laboratories for Structural Biology, Department of Cell Biology, Stanford University School of Medicine, California 94305.
Protein Sci. 1994 Nov;3(11):1938-44. doi: 10.1002/pro.5560031105.
We report an interesting case of structural similarity between 2 small, nonhomologous proteins, the third domain of ovomucoid (ovomucoid) and the C-terminal fragment of ribosomal L7/L12 protein (CTF). The region of similarity consists of a 3-stranded beta-sheet and an alpha-helix. This region is highly similar; the corresponding elements of secondary structure share a common topology, and the RMS difference for "equivalent" C alpha atoms is 1.6 A. Surprisingly, this common structure arises from completely different sequences. For the common core, the sequence identity is less than 3%, and there is neither significant sequence similarity nor similarity in the position or orientation of conserved hydrophobic residues. This superposition raises the question of how 2 entirely different sequences can produce an identical structure. Analyzing this common region in ovomucoid revealed that it is stabilized by disulfide bonds. In contrast, the corresponding structure in CTF is stabilized in the alpha-helix by a composition of residues with high helix-forming propensities. This result suggests that different sequences and different stabilizing interactions can produce an identical structure.
我们报告了一个有趣的案例，即两种小的非同源蛋白质——卵类粘蛋白的第三个结构域（卵类粘蛋白）和核糖体L7/L12蛋白的C端片段（CTF）之间存在结构相似性。相似区域由一个三链β折叠和一个α螺旋组成。该区域高度相似；二级结构的相应元件具有共同的拓扑结构，“等效”Cα原子的均方根偏差为1.6埃。令人惊讶的是，这种共同结构源自完全不同的序列。对于共同核心，序列同一性小于3%，并且在保守疏水残基的位置或方向上既没有显著的序列相似性，也没有相似性。这种叠加引发了一个问题，即两个完全不同的序列如何能产生相同的结构。对卵类粘蛋白中的这个共同区域进行分析发现，它通过二硫键得以稳定。相比之下，CTF中的相应结构在α螺旋中通过具有高螺旋形成倾向的残基组成得以稳定。这一结果表明，不同的序列和不同的稳定相互作用可以产生相同的结构。
