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西藏温泉蛇血红蛋白高原低氧适应性分子机制研究

Study on Molecular Mechanism of Hemoglobin Adaptability of Thermophis baileyi to High Altitude Hypoxia

  • 摘要: 本文结合基因组学、分子进化以及计算生物学等分析方法,对西藏温泉蛇(Thermophis baileyi)血红蛋白(hemoglobin,Hb)基因家族成员、基因簇结构和蛋白质结构等进行研究,探索西藏温泉蛇对高原低氧环境适应的分子机制。结果显示,西藏温泉蛇基因组中包含2个α珠蛋白基因和2个β珠蛋白基因,其中β珠蛋白基因簇高度保守,αA珠蛋白基因在有鳞目祖先分化及形成蛇类和蜥蜴类的过程中发生了基因转座事件,转座后在蛇类中的排列模式为(5′-RREB1,SSR1,αA,RIOK1,DSP-3′)。西藏温泉蛇αD和β2基因分别有2个和4个潜在的正选择位点,其中αD亚基p.Arg9Lys和p.Val36Thr突变使得该亚基血红素口袋体积增大和亲水性升高,这有利于提高O2的运输效率。β2亚基p.Ser53Asn突变导致血红素口袋的亲水性升高,p.Ile112Leu、 p.Thr135Cys和p.Ala139Ser突变使得β2亚基内部稳定性升高,这有利于相应蛋白质亚型在红细胞中的积累。另外,与剑纹带蛇(Thamnophis sirtalis)相比,西藏温泉蛇(αDβ22亚型αβ/αβ间盐桥和氢键数量明显减少,使得T-R态的转变过程易发。综上,西藏温泉蛇αD和β2基因正选择突变导致的蛋白质构象和理化性质的变化可能会使得Hb相应亚型的氧亲和力升高,从而提高低氧条件下氧运输的效率。

     

    Abstract: In this study, genomics, molecular evolution, and computational biology were combined to investigate the molecular mechanisms of hemoglobin(Hb) gene family members, gene cluster structure, and protein structure in the adaptation of Thermophis baileyi to the hypoxic environment on the plateau. The results showed that the genome of T. baileyi contains two α globin genes and two β globin genes, among which the β globin gene cluster was highly conserved. αA globin gene underwent a gene translocation event during the differentiation and formation of snakes and lizards in the ancestral squamates, and the post-translocation arrangement pattern in snakes is(5′-RREB1, SSR1, αA, RIOK1, DSP-3′). There were two and four potential positive selection sites in the αD and β~2 genes of the T. baileyi, respectively, where mutations at the αD subunit p.Arg9Lys and p.Val36Thr positions resulted in an increase in the size and hydrophilicity of the heme pocket, and this mutation was beneficial for improving the O2 transport efficiency. β~2 subunit p.Ser53Asn mutations result in an increase in the hydrophilicity of the heme pocket of this subunit. The β~2 subunit p.Ile112Leu, p.Thr135Cys and p.Ala139Ser mutations led to increase internal stability of the β~2 subunit, which facilitated the accumulation of the corresponding Hb isoforms in erythrocytes. In addition, compared with Thamnophis sirtalis, there was a significant reduction in the number of salt bridges and hydrogen bonds between αβ/αβ of T. baileyi(αDβ~2)2 isoforms, which would make the transition process of T-R state easier to occur. In conclusion, the changes in protein conformation and physicochemical properties caused by positive selection mutations in the αD and β~2 genes of T. baileyi may lead to an increase in the oxygen affinity of the corresponding of Hb isoforms, thereby improving the efficiency of oxygen transport under extreme hypoxic conditions.

     

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