水稻和拟南芥中几丁质酶的分析

几丁质酶（EC3．2．1．14）是一种降解几丁质的糖苷酶，广泛存在于各种生物体中，并在植物中对病原真菌起重要抗性作用。首先通过BLAST在GenBank中对其同源性进行搜索，用SMART分析其结构。基于水稻和拟南芥的基因组注释，借助4个生物学软件（SignalP3．0，TMHMM2．0，TargetP1．1andbig—PiPredictor），分析了水稻所有37条和拟南芥所有24条几丁质酶序列，发现有些几丁质酶都分泌到细胞外，有些定位于液泡中，水稻中仅25条和拟南芥中仅16条几丁质酶序列有信号肽，这些信号肽的平均长度为24．8aa。利用ClustalX和MEGA3．1两个生物软件分析了59条几丁质酶序列和25条标准几丁质酶的系统发育关系，这些几丁质酶可分为Ⅰ、Ⅱ、Ⅲ、Ⅳ、Ⅴ和Ⅵ等6大类。这种聚类结果与几丁质酶传统分为7类有些差异。通过对6大类中各个氨基酸残基的分析，发现丙氨酸、甘氨酸、丝氨酸和亮氨酸的使用频率在每类中都非常高，而蛋氨酸、组氨酸、色氨酸和半胱氨酸均低于20％。各大类中彼此之间的某些氨基酸使用频率明显不同，Ⅰ-Ⅵ分别富含丙氨酸、缬氨酸、亮氨酸、半胱氨酸、丝氨酸和赖氨酸。

Chitinases in Oryza sativa ssp. japonica and Arabidopsis thaliana

Chitinases (EC3.2.1.14), found in a wide range of organisms, catalyze the hydrolysis of chitin and play a major role in defense mechanisms against fungal pathogens. The alignment and typical domains were analyzed using basic local alignment search tool (BLAST) and simple modular architecture research tool (SMART), respectively. On the basis of the annotations of rice (Oryza sativa L.) and Arabidopsis genomic sequences and using the bio-software SignalP3.0, TMHMM2.0, TargetP1.1, and big-Pi Predictor, 25 out of 37 and 16 out of 24 open reading frames (ORFs) with chitinase activity from rice and Arabidopsis, respectively, were predicted to have signal peptides (SPs), which have an average of 24.8 amino acids at the N-terminal region. Some of the chitinases were secreted extracellularly, whereas some were located in the vacuole. The phylogenic relationship was analyzed with 61 ORFs and 25 known chitinases and they were classified into 6 clusters using Clustal X and MEGA3.1. This classification is not completely consistent when compared with the traditional system that classifies the chitinases into 7 classes. The frequency of distribution of amino acid residues was distinct in different clusters. The contents of alanine, glycine, serine, and leucine were very high in each cluster, whereas the contents of methionine, histidine, tryptophan, and cysteine were lower than 20%. Each cluster had distinct amino acid characteristics. Alanine, valine, leucine, cysteine, serine, and lysine were rich in Clusters I to VI, respectively.