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.