Carugo O, Lu S, Luo J, Gu X, Liang S, Strobl S, Pongor S
International Centre for Genetic Engineering and Biotechnology, Padriciano 99, Trieste Department of General Chemistry, University of Pavia, Pavia, Italy.
Protein Eng. 2001 Sep;14(9):639-46. doi: 10.1093/protein/14.9.639.
The three-dimensional structure of the amaranth alpha-amylase inhibitor (AAI) adopts a knottin fold of abcabc topology. Upon binding to alpha-amylase, it adopts a more compact conformation characterized by an increased number of intramolecular hydrogen bonds, a decreased volume and in addition a trans to cis isomerization of Pro20. A systematic analysis of the 3-D structural databanks revealed that similar proteins and domains share with AAI the characteristic presence of proline residues, many of which are in a cis backbone conformation. As these proteins fulfil a variety of functional roles and are expressed in very different organisms, we conclude that the structure of the knottin fold, including the propensity of the cis bond, are the result of convergent evolution.
苋属α-淀粉酶抑制剂（AAI）的三维结构采用abcabc拓扑结构的扭结蛋白折叠。与α-淀粉酶结合后，它会呈现出更紧凑的构象，其特征是分子内氢键数量增加、体积减小，此外Pro20还会发生反式到顺式的异构化。对三维结构数据库的系统分析表明，类似的蛋白质和结构域与AAI一样，都具有脯氨酸残基的特征性存在，其中许多脯氨酸残基处于顺式主链构象。由于这些蛋白质发挥着多种功能作用，并且在非常不同的生物体中表达，我们得出结论，扭结蛋白折叠的结构，包括顺式键的倾向，是趋同进化的结果。
