Abstract：
Myoglobin (Mb) mediates oxygen diffusion and storage in muscle tissue and thus is important for the energy utilization and activity of animals. Birds generally have a high body temperature, and most species also possess the capability of powered flight. Both of these require high levels of aerobic metabolism. Within endothermic mammals, bats also independently evolved flight. Although the functional evolution of myoglobins in deep-diving amniote vertebrates has been well-studied, the functional evolution of myoglobin since the origins of both birds and bats is unclear. Here, with Mb-coding sequences from >200 extant amniote species, we reconstructed ancestral sequences to estimate the functional properties of myoglobin through amniote evolution. A dramatic change in net surface charge on myoglobin occurred during the origin of Aves, which might have been driven by positively selected amino acid substitutions that occurred on the lineage leading to all birds. However, in bats, no change in net surface charge occurred and instead, the Mb genes show evidence of strong purifying selection. The increased net surface charge on bird myoglobins implies an adaptation to flight-related endothermic and higher body temperatures, possibly by reducing harmful protein aggregations. Different from the findings of net surface charge, myoglobins of extant birds show lower stability compared with other amniotes, which probably accelerates the rate of oxygen utilization in muscles. In bats and other mammals, higher stability of Mb may be an alternative pathway for adaptation to endothermy, indicating divergent evolution of myoglobin in birds and bats.
摘要：
肌红蛋白（Mb）介导氧气在肌肉组织中的扩散和储存，因此对于动物的能量利用和活动很重要。鸟类通常体温很高，大多数物种也具有动力飞行的能力。这两者都需要高水平的有氧代谢。在吸热的哺乳动物中，蝙蝠也独立进化飞行。尽管深潜羊膜脊椎动物中肌球蛋白的功能进化已经得到了充分的研究，自鸟类和蝙蝠起源以来，肌红蛋白的功能演变尚不清楚。这里,Mb编码序列来自>200个现存的羊水物种，我们重建了祖先序列，通过羊膜进化来估计肌红蛋白的功能特性。肌红蛋白上的净表面电荷发生了戏剧性的变化，这可能是由在导致所有鸟类的谱系上发生的积极选择的氨基酸取代所驱动的。然而,在蝙蝠中，净表面电荷没有发生变化，相反，Mb基因显示强纯化选择的证据。鸟类肌球蛋白的净表面电荷增加意味着适应与飞行相关的吸热和更高的体温，可能是通过减少有害的蛋白质聚集。与净表面电荷的发现不同，与其他羊膜相比，现存鸟类的肌动蛋白显示出更低的稳定性，这可能会加速肌肉中氧气的利用率。在蝙蝠和其他哺乳动物中，Mb的更高稳定性可能是适应吸热的替代途径，表明鸟类和蝙蝠中肌红蛋白的不同进化。
