α-Tocopherol transfer protein (α-TTP)

alpha-Tocopherol transfer protein (alpha-TTP) is so far the only known protein that specifically recognizes alpha-tocopherol (alpha-Toc), the most abundant and most biologically active form of vitamin E, in higher animals. alpha-TTP is highly expressed in the liver where alpha-TTP selects alpha-Toc among vitamin E forms taken up via plasma lipoproteins and promotes its secretion to circulating lipoproteins. Thus, alpha-TTP is a major determinant of plasma alpha-Toc concentrations. Familial vitamin E deficiency, also called Ataxia with vitamin E deficiency, is caused by mutations in the alpha-TTP gene. More than 20 different mutations have been found in the alpha-TTP gene worldwide, among which some missense mutations provided valuable clues to elucidate the molecular mechanisms underlying intracellular alpha-Toc transport. In hepatocytes, alpha-TTP catalyzes the vectorial transport of alpha-Toc from the endocytotic compartment to the plasma membrane (PM) by targeting phosphatidylinositol phosphates (PIPs) such as PI(4,5) P-2. By binding PIPs at the PM, alpha-TTP opens the lid covering the hydrophobic pocket, thus facilitating the release of bound alpha-Toc to the PM.

Automated summary

Alpha-Tocopherol transfer protein (alpha-TTP) is the only known protein that specifically recognizes alpha-tocopherol, playing a major role in determining plasma alpha-Toc concentrations. Mutations in the alpha-TTP gene cause familial vitamin E deficiency. In hepatocytes, alpha-TTP facilitates the vectorial transport of alpha-Toc by targeting phosphatidylinositol phosphates at the plasma membrane.