Department of Chemistry, University of Pavia, viale Taramelli12, I-27100 Pavia, Italy ; Department of Structural and Computational Biology, Max F. Perutz Laboratories, Vienna University, Campus Vienna Biocenter 5, A-1030 Vienna, Austria.
Comput Struct Biotechnol J. 2013 Aug 14;8:e201308001. doi: 10.5936/csbj.201308001. eCollection 2013.
Although it is reasonable to expect that the frequency of a generic dipeptide XY in proteins is the same of its counterpart YX, on the basis of an accurate statistical analysis of a large number of protein sequences, it appears that some dipeptides XY are considerably more frequent than their mirror images YX, referred to as antidipeptides. Given that it has been verified that this unexpected anisotropic frequency of occurrence is unbiased by the type of protein sequences that are analyzed, it is possible to conclude that this is a genuine phenomenon. Nevertheless, it was impossible to find the mechanism underlying this unexpected phenomenon, which does not seem to be related to diverse conformational propensities, to the different conformational flexibility of the peptide/antidipeptide pair, to dissimilar accessibility to the solvent or to gene random mutations.
尽管根据对大量蛋白质序列的准确统计分析，可以合理地预期蛋白质中通用二肽 XY 的出现频率与其镜像 YX 相同，但事实似乎表明，某些二肽 XY 的出现频率明显高于其镜像 YX，这些二肽被称为反二肽。鉴于已经验证，这种出乎意料的各向异性出现频率不受所分析的蛋白质序列类型的影响，因此可以得出这是一种真实现象的结论。然而，人们无法找到这种出乎意料的现象背后的机制，这似乎与不同的构象倾向、肽/反肽对的不同构象灵活性、对溶剂的不同可及性或基因随机突变无关。
