脊椎动物TYR基因的序列特征与正选择位点鉴定

酪氨酸酶是一种含铜金属酶,它广泛存在于各种生物中,是黑色素生物合成的关键酶.利用生物信息学手段详细剖析了脊椎动物TYR基因的序列和进化特性,并模拟了其蛋白的三位结构.系统发生研究显示,脊椎动物TYR基因与物种进化关系之间具有较高的一致性.基因结构分析表明,绝大多数脊椎动物TYR基因有5个外显子,但DrTYR和OlTYR有6个外显子,而Ss TYR有9个外显子.蛋白序列特征分析显示,脊椎动物TYR蛋白均具有典型的TYROSINASE结构域,但不同物种具有特异的保守基序组织模式,其中保守基序13是哺乳类动物TYR蛋白所特有的.位点模型没有检测出正选择位点,但分支位点模型已经检测出马与猪的祖先支(26个正选择位点)、猪进化分支(27个正选择位点)以及斑胸草雀与鸡的祖先支(1个正选择位点)均经历了适应性进化.这些正选择位点虽然被定位于不同二级结构内,但在三维结构中它们分布在相对集中的区域内,很可能与特定功能密切相关.

Sequence features and selective pressure of the TYR genes in vertebrates

Tyrosinase, widely presented in various organisms, is a copper-containing enzyme that is involved mainly in the biosynthesis of melanin. Bioinformatics method was used to investigate the sequence features and evolutionary pattern of vertebrate TYR genes and to construct three dimensional structures of representative proteins. Phylogenetic analysis indicated that gene tree of vertebrate TYR proteins was highly consistent with species tree. Gene structure analysis showed that 5 exons were shared by most vertebrate TYR genes, DrTYR and OlTYR genes had 6 exons, and SsTYR gene had 9 exons. Analysis of protein sequence demonstrated that the common TYROSINASE domain was shared by vertebrate TYR proteins. In addition, different TYR proteins from distinct species had conserved motif organizations, but Motif 13 is specific to mammal TYR proteins. Selection pressure analysis was performed on the vertebrate TYR proteins using sitemodel and branch-site model. No amino acid sites were under positive selection via site model. However, three branches under positive selection were identified by branch-site model. Accordingly, 26 positively selected sites were identified from the ancestral branch of horse and pig. 27 positively selected sites were found from the pig branch. Only one positively selected site was identified from the ancestral branch of chicken and Zebra finch. These positively selected sites were distributed on different primary and secondary structures of TYR proteins, but were intensively distributed on the same area of three dimensional structures, suggesting that these sites were closely coupled to specific functions.