Research Center for High Altitude Medicine, Qinghai University Medical College, Xining 810001, Qinghai, China.
Gene. 2014 Jan 10;533(2):532-7. doi: 10.1016/j.gene.2013.09.030. Epub 2013 Sep 26.
The Tibetan antelope (Pantholops hodgsonii) is a hypoxia-tolerant species that lives at an altitude of 4,000-5,000 m above sea level on the Qinghai-Tibetan plateau. Myoglobin is an oxygen-binding cytoplasmic hemoprotein that is abundantly expressed in oxidative skeletal and cardiac myocytes. Numerous studies have implicated that hypoxia regulates myoglobin expression to allow adaptation to conditions of hypoxic stress. Few studies have yet looked at the effect of myoglobin on the adaptation to severe environmental stress on TA. To investigate how the Tibetan antelope (TA) has adapted to a high altitude environment at the molecular level, we cloned and analyzed the myoglobin gene from TA, compared the expression of myoglobin mRNA and protein in cardiac and skeletal muscle between TA and low altitude sheep. The results indicated that the full-length myoglobin cDNA is composed of 1154 bp with a 111 bp 5' untranslated region (UTR), a 578 bp 3' UTR and a 465 bp open reading frame (ORF) encoding a polypeptide of 154 amino acid residues with a predicted molecular weight of 17.05 kD. The TA myoglobin cDNA sequence and the deduced amino acid sequence were highly homologous with that of other species. When comparing the myoglobin sequence from TA with the Ovis aries myoglobin sequence, variations were observed at codons 21 (GGT→GAT) and 78 (GAA→AAG), and these variations lead to changes in the corresponding amino acids, i.e., Gly→Asp and Glu→Lys, respectively. But these amino acid substitutions are unlikely to effect the ability of binding oxygen because their location is less important, which is revealed by the secondary structure and 3D structure of TA myoglobin elaborated by homology modeling. However, the results of myoglobin expression in cardiac and skeletal muscles showed that they were both significantly higher than that in plain sheep not only in mRNA but also protein level. We speculated that the higher expression of myoglobin in TA cardiac and skeletal muscles improves their ability to obtain and store oxygen under hypoxic conditions. This study indicated that TA didn't improve the ability of carrying oxygen by changing the molecular structure of myoglobin, but through increasing the expression of myoglobin in cardiac and skeletal muscles.
藏羚羊（Pantholops hodgsonii）是一种耐缺氧物种，生活在海拔 4000-5000 米的青藏高原上。肌红蛋白是一种富含氧的细胞质血红素蛋白，在氧化的骨骼肌和心肌细胞中大量表达。许多研究表明，缺氧调节肌红蛋白的表达，以适应缺氧应激条件。然而，很少有研究关注肌红蛋白对藏羚羊适应极端环境压力的影响。为了从分子水平上研究藏羚羊（TA）如何适应高海拔环境，我们从 TA 中克隆并分析了肌红蛋白基因，并比较了 TA 和低海拔绵羊心脏和骨骼肌中肌红蛋白 mRNA 和蛋白的表达。结果表明，全长肌红蛋白 cDNA 由 1154bp 组成，包含 111bp 的 5'非翻译区（UTR）、578bp 的 3'UTR 和 465bp 的开放阅读框（ORF），编码 154 个氨基酸残基的多肽，预测分子量为 17.05kD。TA 肌红蛋白 cDNA 序列和推导的氨基酸序列与其他物种高度同源。当将 TA 的肌红蛋白序列与 Ovis aries 的肌红蛋白序列进行比较时，观察到密码子 21（GGT→GAT）和 78（GAA→AAG）发生了变异，这些变异导致相应氨基酸发生变化，即 Gly→Asp 和 Glu→Lys。但这些氨基酸替换不太可能影响结合氧的能力，因为它们的位置不太重要，这一点通过同源建模阐述的 TA 肌红蛋白的二级结构和 3D 结构得到了揭示。然而，心脏和骨骼肌中肌红蛋白表达的结果表明，无论是在 mRNA 还是蛋白水平上，它们都明显高于平原绵羊。我们推测，TA 心脏和骨骼肌中肌红蛋白的高表达提高了它们在缺氧条件下获取和储存氧气的能力。本研究表明，TA 并没有通过改变肌红蛋白的分子结构来提高携氧能力，而是通过增加心脏和骨骼肌中肌红蛋白的表达来实现。
