A New Homotetramer Hemoglobin in the Pulmonary Surfactant of Plateau Zokors (Myospalax Baileyi)

The plateau zokor (Myospalax baileyi) is a native species to the Qinghai-Tibetan Plateau, inhabiting hypoxia and hypercapnia sealed subterranean burrows that pose several unique physiological challenges. In this study, we observed a novel heme-containing protein in the pulmonary surfactant (PS) of plateau zokor, identified the encoding gene of the protein, predicted its origination and structure, verified its expression in alveolar epithelial cells, and determined the protein's affinity to oxygen and its effect on the oxygen-dissolving capability in the PS of plateau zokors. The protein is an unusual homotetramer hemoglobin consisting of four gamma-like subunits, and the subunit is encoded by a paralog gene of gamma, that is gamma-like. The divergence time of gamma-like from gamma is estimated by the molecular clock to be about 2.45 Mya. The generation of gamma-like in plateau zokors might well relate to long-time stress of the high land hypoxia. Unlike gamma, the gamma-like has a hypoxia response element (HRE) and a lung tissue-specific enhancer in its upstream region, and it is expressed specifically in lung tissues and up-regulated by hypoxia. The protein is named as gamma(4)-like which is expressed specifically in Alveolar epithelial type II (ATII) cells and secreted into the alveolar cavities through the osmiophilic multilamellar body (LBs). The gamma(4)-like has a higher affinity to oxygen, and that increases significantly oxygen-dissolving capability in the PS of plateau zokors by its oxygenation function, which might be beneficial for the plateau zokors to obtain oxygen from the severe hypoxia environments by facilitating oxygen diffusion from alveoli to blood.

Automated summary

This study identified a novel heme-containing protein, named gamma(4)-like, in the pulmonary surfactant of plateau zokors. The protein has a higher affinity to oxygen and increases the oxygen-dissolving capability, which benefits the zokors in obtaining oxygen in the low-oxygen environment.