蓝细菌16S rRNA双甲基化酶基因ksgA的进化分析、蛋白结构预测及功能验证

发布时间：2018-06-09 23:53

本文选题：ksgA + 蓝细菌　；参考：《华中农业大学》2015年硕士论文

【摘要】：作为地球上最古老的生物之一,蓝细菌种类多样,是生态环境中重要的微生物类群。目前,关于蓝细菌的分子进化还存在很多争议和空白。KsgA/Dim1家族的双甲基化酶是一个典型的S-腺苷甲硫氨酸(SAM)依赖的Ⅰ类甲基转移酶,催化核糖体小亚基rRNA末端茎环上两个相邻腺嘌呤的双甲基化。这两个碱基的双甲基化修饰是核糖体小亚基rRNA仅有的三个高度保守的碱基修饰中的两个。本研究对已测序的37种蓝细菌KsgA甲基化酶基因和16S rDNA进行了序列比对和进化分析,结果显示蓝细菌ksgA基因与16S rDNA进化分支高度相似,且体现出蓝细菌进化的聚类特征。本研究同时对蓝细菌KsgA蛋白进行了结构预测、保守模体及催化活性位点分析,显示蓝细菌KsgA甲基化酶与其它物种的KsgA/Dim1家族蛋白拥有高度相似的结构：均包含N端与C端两个结构域,N端是典型而保守的SAM依赖的甲基转移酶结构域；C端的序列和结构则均呈现相对多样化。根据序列分析和结构预测的结果,本研究中选择克隆了单细胞的集胞蓝细菌Synechocystis sp.PCC6803.丝状能分化异形胞固氮的鱼腥蓝细菌Anabaena sp.PCC120,以及单细胞棒状的细长聚球蓝细菌Synechococcus elongates sp.PCC7942的ksgA基因,分别对大肠杆菌的ksgA突变体进行异源互补以初步验证ksgA在蓝细菌中的功能,实验中发现它们均能在一定程度上互补大肠杆菌ksgA基因突变体的表型。本研究通过对蓝细菌中KsgA/Dim1蛋白质家族的研究为进一步理解蛋白质功能与结构协同进化的机制和蓝细菌的演化历程补充了理论依据并提供了实验证据。
[Abstract]:As one of the oldest organisms on the earth, cyanobacteria are an important microbial group in the ecological environment. At present, there are many controversies about the molecular evolution of cyanobacteria and the blank. KsgA / Dim1 family of dimethylases is a typical type I methyltransferase dependent on S- adenosine methionine (SAM). Catalyze the dimethylation of two adjacent adenines in the terminal stem ring of ribosomal small subunit rRNA. The dimethylation modification of these two bases is one of only three highly conserved modifications of ribosomal small subunit rRNA. In this study, the sequence alignment and evolution analysis of KsgA methylase gene and 16s rDNA of 37 species of cyanobacteria were carried out. The results showed that the ksgA gene of cyanobacteria was highly similar to the evolutionary branch of 16s rDNA, and showed the clustering characteristics of the evolution of cyanobacteria. At the same time, the structure of cyanobacteria KsgA protein was predicted, and the conserved motifs and catalytic activity sites were analyzed. It shows that the KsgA methylase of the cyanobacteria has a highly similar structure to the KsgA / Dim1 family of other species: both N-terminal and C-terminal N-terminal are typical and conserved SAM-dependent methyltransferase domain C-terminal sequences. And the structure is relatively diverse. According to the results of sequence analysis and structure prediction, Synechocystis sp. PCC6803 was cloned from single cell. Anabaena sp. PCC120, a filamentous bacterium capable of heterocytic nitrogen fixation, and ksgA gene of Synechococcus elongates sp. PCC7942, a single cell rod-like bacterium, were used to complement the ksgA mutants of Escherichia coli to preliminarily verify the function of ksgA in cyanobacteria. It was found that they could complement the phenotypes of E. coli ksgA gene mutants to some extent. In this study, the study of KsgA / Dim1 protein family in cyanobacteria provides theoretical basis and experimental evidence for further understanding the mechanism of protein function and structure coevolution and the evolution process of cyanobacteria.
【学位授予单位】：华中农业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：Q936

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