Agri-Bioinformatics Promotion Programme, Department of Agricultural Biotechnology, Assam Agricultural University, Jorhat, 785013 Assam, India.
J Mol Model. 2012 Nov;18(11):4761-80. doi: 10.1007/s00894-012-1470-8. Epub 2012 Jun 9.
Glycoside hydrolase family 19 chitinases (EC 3.2.1.14) widely distributed in plants, bacteria and viruses catalyse the hydrolysis of chitin and play a major role in plant defense mechanisms and development. Rice possesses several classes of chitinase, out of which a single structure of class I has been reported in PDB to date. In the present study an attempt was made to gain more insight into the structure, function and evolution of class I, II and IV chitinases of GH family 19 from rice. The three-dimensional structures of chitinases were modelled and validated based on available X-ray crystal structures. The structural study revealed that they are highly α-helical and bilobed in nature. These enzymes are single or multi domain and multi-functional in which chitin-binding domain (CBD) and catalytic domain (CatD) are present in class I and IV whereas class II lacks CBD. The CatD possesses a catalytic triad which is thought to be involved in catalytic process. Loop III, which is common in all three classes of chitinases, reflects that it may play a significant role in their function. Our study also confirms that the absence and presence of different loops in GH family 19 of rice may be responsible for various sized products. Molecular phylogeny revealed chitinases in monocotyledons and dicotyledons differed from each other forming two different clusters and may have evolved differentially. More structural study of this enzyme from different plants is required to enhance the knowledge of catalytic mechanism and substrate binding.
糖苷水解酶家族 19 几丁质酶（EC 3.2.1.14）广泛分布于植物、细菌和病毒中，催化几丁质的水解，在植物防御机制和发育中发挥重要作用。水稻拥有几丁质酶的几个家族，迄今为止，在 PDB 中仅报道了 I 类的单个结构。本研究试图更深入地了解水稻 GH 家族 19 的 I、II 和 IV 类几丁质酶的结构、功能和进化。基于现有的 X 射线晶体结构，对几丁质酶的三维结构进行了建模和验证。结构研究表明，它们高度α-螺旋化，本质上是双叶的。这些酶是单或多结构域的多功能酶，其中 I 类和 IV 类具有几丁质结合域（CBD）和催化域（CatD），而 II 类则缺乏 CBD。CatD 具有一个催化三联体，被认为参与催化过程。所有三种几丁质酶都存在的环 III 表明它可能在它们的功能中发挥重要作用。我们的研究还证实，水稻 GH 家族 19 中不同环的缺失和存在可能导致不同大小的产物。分子系统发育表明，单子叶植物和双子叶植物中的几丁质酶彼此不同，形成两个不同的聚类，并且可能具有不同的进化方式。需要对来自不同植物的这种酶进行更多的结构研究，以增强对催化机制和底物结合的了解。
