棕颈雪雀血红蛋白高原低氧适应的分子进化机制

Molecular Evolutionary Mechanism of Hemoglobin Adaptation to High Altitude Hypoxia in Pyrgilauda ruficollis

血红蛋白(hemoglobin)在动物机体氧气转运中起关键作用。本文运用基因组学、分子进化学、分子动力学和计算生物学等分析方法对棕颈雪雀(Pyrgilauda ruficollis)Hb基因家族成员、基因簇结构以及Hb蛋白质结构等展开研究,旨在阐明棕颈雪雀Hb适应高原低氧环境的机制。结果表明,棕颈雪雀Hb的α基因簇(5′-α^(E)、α^(D)、α^(A)-3′)和β基因簇(5′-ρ、β^(H)、β^(A)、ε-3′)均保留了在鸟类祖先中的分布模式;Hb的α^(A)亚基有7个潜在的正选择突变位点,其中有5个位点(p.Pro5Ser、p.Ala6Ser、p.Ala27Gly、p.Asp28Glu、p.Ala35Thr)均由疏水氨基酸突变为亲水氨基酸,是α^(A)亚基亲水性升高的主要原因。p.Pro45Ala突变增大了C螺旋和F螺旋之间的距离,使得α^(A)亚基活性中心体积由麻雀的0.683 nm^(3)增大至棕颈雪雀的0.711 nm^(3),亲水性升高和活性中心体积增大有利于棕颈雪雀(α^(A)β^(A))_(2)亚型Hb在红细胞中的积累和气体交换;p.Ala27Gly和p.Ala35Thr突变使得棕颈雪雀(α^(A)β^(A))_(2)亚型Hb二聚体间氢键数量减少,使Hb从T态(tense state)到R态(relaxed state)的转变过程更易发生。推测上述突变导致的Hb物理化学和结构的变化均能使得相应亚型的固有氧亲和力升高,这可能是棕颈雪雀Hb适应高原低氧环境的主要机制。

Hemoglobin(Hb)plays a key role in oxygen transport in animals.In this study,the members of Hb gene family,the structure of gene cluster and the protein structure of Pyrgilauda ruficollis were studied by genomics,molecular evolution,molecular dynamics and computational biology.The purpose was to explain the mechanism of Hb adaptation to high altitude hypoxia environment in P.ruficollis.The results showed thatα(5′-α^(E),α^(D),α^(A)-3′)andβ(5′-ρ,β^(H),β^(A),ε-3′)gene clusters of P.ruficollis Hb retained their distribution patterns in the ancestors of birds.Hbα^(A)had seven mutation sites of potential positive selection,among which 5 sites(p.Pro5Ser、p.Ala6Ser、p.Ala27Gly、p.Asp28Glu、p.Ala35Thr)mutated from hydrophobic amino acids into hydrophilic amino acids,which was the main reason for hydrophilicity increase ofα^(A)subunit.Mutation of p.Pro45Ala increased the distance between C and F helices,which caused the increase of active center volume ofα^(A)subunit(from 0.683 nm^(3) of Passer domesticus to 0.711 nm^(3)of Pyrgilauda ruficollis).The increase of hydrophilicity and active center volume were beneficial to the accumulation of(α^(A)β^(A))_(2)subtype of Hb and gas exchange in red blood cells.Two mutations including p.Ala27Gly and p.Ala35Thr reduced the number of hydrogen bonds between the dimers of the(α^(A)β^(A))_(2)subtype of Hb in Pyrgilauda ruficollis,which made the transition of Hb from T state(tense state)to R state(relaxed state)easier.It is speculated that the changes of physical and chemical properties and conformation of Hb caused by the above mutations could improve aerobic affinity of the corresponding subtypes,which may be the main mechanism of Hb adaptation to high altitude hypoxia environment in Pyrgilauda ruficollis.