红尾沙蜥鸟氨酸脱羧酶1高原适应的分子机理

Molecular mechanism of plateau adaptation of ornithine decarboxylase 1 in Phrynocephalus erythrurus

运用基因组学、转录组学、分子进化和计算生物学等分析方法对红尾沙蜥鸟氨酸脱羧酶1(ODC1)基因结构、表达量、正选择位点以及蛋白质理化性质和结构展开研究,旨在阐明ODC1基因在沙蜥属不同海拔物种中的表达模式和在高海拔红尾沙蜥中低氧适应的分子机理.结果显示,ODC1基因在红尾沙蜥4个组织中的表达量约为荒漠沙蜥的2.25、1.14、2.51和4.82倍,其中在肝脏、脑和心脏组织中的表达量显著高于荒漠沙蜥.红尾沙蜥ODC1蛋白质的总平均亲水性系数和不稳定性系数分别为-0.122和46.51,较荒漠沙蜥亲水性更高、结构更稳定.红尾沙蜥ODC1蛋白质位于β/α桶状结构域的222Gly→Ala(潜在的正选择位点)和228Ser→Asn两个突变使得该区域结构更紧凑,并使得蛋白质活性中心体积由荒漠沙蜥的0.7343 nm^(3)增大到红尾沙蜥的0.7448 nm^(3),且活性中心亲水性增大.位于β层片结构域的446Ile→Met氨基酸突变使得该区域的无规则卷曲被α螺旋取代,蛋白质稳定性增强.红尾沙蜥ODC1基因表达量的显著上调和氨基酸突变导致的蛋白质结构稳定性增强均有利于蛋白质在溶液中积累到较高的浓度.氨基酸突变导致的红尾沙蜥ODC1蛋白质活性中心体积增大和亲水性升高对提高该酶的催化效率有一定作用.红尾沙蜥ODC1基因的高表达和蛋白质结构的改变,可能通过提高多胺物质的生物合成,对低氧引起的机体组织损伤后的修复和肺动脉高压的缓解起重要作用.

To clarify the expression pattern of ornithine decarboxylase-1(ODC1)gene in species at different altitudes and the molecular mechanism of adaptation to high altitude hypoxia in Phrynocephalus erythrurus,the gene structure,expression level,selection pressure,physicochemical properties and structure of ODC1 gene in P.erythrurus were studied by combining genomics,transcriptomics,molecular evolution analysis and computational biology.The expression level of ODC1 gene in the four organs of P.erythrurus was about 2.25,1.14,2.51 and 4.82 times of that of P.przewalskii,and the expression levels in the liver,brain and heart tissues were significantly higher than those in the P.przewalskii.The ODC1 protein grand average of hydropathicity and instability index of P.erythrurus was-0.122 and 46.51,respec-tively,which were more hydrophilic and stable than P.przewalskii.222Gly→Ala(potential positive selection site)and 228Ser→Asn located at theβ/αbarrel domain were two mutation sites of ODC1 protein in P.erythrurus,which rendered this domain more compact;the protein active center volume increased from 0.7343 nm^(3)(in P.przewalskii)to 0.7448 nm^(3)(in P.erythrurus),and the hydrophilicity of the active center increased.The 446Ile→Met amino acid mutation in theβ-lamella domain resulted in the replacement of the random coil in this region by theα-helix.The significant up-regulation of ODC1 gene expression in P.erythrurus and the enhanced protein structure stability caused by amino acid mutation were both conducive to the protein accumulation to a higher concentration.The increased volume of ODC1 protein's active center in P.erythrurus caused by amino acid mutation had some effect on improving the catalysis of ODC1.The up-regulation of ODC1 gene expression in P.erythrurus and changes in the physicochemical properties and structure of ODC1 were possibly one of strategies for adapting to the special environment characterized by high altitude hypoxia.The high expression of ODC1 gene and the change in the protein structure in the P.erythrurus might play an important role in the repair of tissue damage caused by hypoxia and the relief of pulmonary hypertension by improving the biosynthesis of polyamines.