α-Tocopherol transfer protein (α-TTP).

Area of Science:

• Biochemistry
• Molecular Biology
• Genetics

Background:

• Alpha-tocopherol transfer protein (α-TTP) is the sole known protein specifically binding α-tocopherol (α-Toc), the most active vitamin E form.
• α-TTP is primarily expressed in the liver, playing a key role in selecting and secreting α-Toc into circulation, thus determining plasma concentrations.
• Genetic mutations in α-TTP cause familial vitamin E deficiency (Ataxia with vitamin E deficiency).

Purpose of the Study:

• To elucidate the molecular mechanisms of intracellular α-Toc transport mediated by α-TTP.
• To investigate how α-TTP facilitates α-Toc release to the plasma membrane in hepatocytes.

Main Methods:

• Analysis of missense mutations in the α-TTP gene.
• Studying the targeting of α-TTP to phosphatidylinositol phosphates (PIPs) at the hepatocyte plasma membrane.

Main Results:

• α-TTP mediates vectorial transport of α-Toc from endocytotic compartments to the plasma membrane.
• Binding of PIPs, specifically PI(4,5)P2, at the plasma membrane is essential for α-TTP function.
• PIPs binding causes a conformational change in α-TTP, opening its hydrophobic pocket and releasing α-Toc.

Conclusions:

• α-TTP utilizes PIPs at the plasma membrane to facilitate the release of α-Toc for secretion.
• Understanding this mechanism is key to addressing vitamin E deficiency disorders caused by α-TTP mutations.