Structure, Expression and Functions of Bovine Alpha-Tocopherol Transfer Protein (α-TTP)

α-tocopherol transfer protein (α-TTP) of bovine consists of 282 amino acids with 98% and 83% identities to sheep and rat orthologs, respectively. Bovine α-TTP has an additional 5 amino acids (GEEVT) at the C terminus, which rat, human, mouse α-TTPs do not have. The Blast research suggested that the C-terminal sequences of α-TTP are specific for Cetartiodactyla animals. Bovine α-TTP mRNA and protein were expressed most strongly in liver, and also in lung, whereas expression of α-TTP mRNA and protein are reported to be very weak or absent in human and rodent lungs. In the lung, immunostaining suggested that α-TTP is expressed specifically in alveolar walls, which consists of alveolar cells, epithelial cells of small bronchi, and endothelial cells of pulmonary blood vessels. These results suggest that, in the lung, α-TTP is involved in supplying vitamin E to alveolar surfactant in order to protect the lung tissue from oxidative stress, and that this role may be more important in bovines than in other mammals.

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