Detection, Characterization and Evolution of Internal Repeats in Chitinases of Known 3-D Structure

Chitinase proteins have evolved and diversified almost in all organisms ranging from prokaryotes to eukaryotes. During evolution, internal repeats may appear in amino acid sequences of proteins which alter the structural and functional features. Here we deciphered the internal repeats from Chitinase and characterized the structural similarities between them. Out of 24 diverse Chitinase sequences selected, six sequences (2CJL, 2DSK, 2XVP, 2Z37, 3EBV and 3HBE) did not contain any internal repeats of amino acid sequences. Ten sequences contained repeats of length <50, and the remaining 8 sequences contained repeat length between 50 and 100 residues. Two Chitinase sequences, 1ITX and 3SIM, were found to be structurally similar when analyzed using secondary structure of Chitinase from secondary and 3-Dimensional structure database of Protein Data Bank. Internal repeats of 3N17 and 1O6I were also involved in the ligand-binding site of those Chitinase proteins, respectively. Our analyses enhance our understanding towards the identification of structural characteristics of internal repeats in Chitinase proteins.

几丁质酶（Chitinase）蛋白几乎在从原核生物（prokaryotes）到真核生物（eukaryotes）的所有生物体中均经历了演化与多样化。在演化过程中，蛋白质的氨基酸（amino acid）序列中可能出现内部重复序列，此类序列会改变其结构与功能特征。本研究解析了几丁质酶的内部重复序列，并对其相互间的结构相似性进行了表征。在选取的24条不同几丁质酶序列中，6条序列（2CJL、2DSK、2XVP、2Z37、3EBV及3HBE）未包含任何氨基酸序列内部重复；10条序列的重复序列长度小于50个氨基酸残基（residues），剩余8条序列的重复序列长度介于50至100个氨基酸残基之间。基于蛋白质数据银行（Protein Data Bank）的二级与三维结构数据库中的几丁质酶二级及三维结构进行分析，发现两条几丁质酶序列1ITX与3SIM的结构相似。3N17与1O6I的内部重复序列分别参与了对应几丁质酶蛋白的配体结合位点（ligand-binding site）。本研究的分析结果加深了我们对几丁质酶蛋白内部重复序列结构特征鉴定的认知。