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Related Concept Videos

Protein Transport to the Thylakoids01:22

Protein Transport to the Thylakoids

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Thylakoids are membrane-bound sac-like structures within the chloroplast that serve as sites for photosynthesis. Thylakoid lumen contains many electron transport proteins and is enclosed by a thylakoid membrane rich in the light-harvesting complex. Proteins targeted to the thylakoids are transported as precursors and are sorted by the general TOC/TIC import pathway. Once the precursor reaches the stroma, stromal processing peptidases remove their transit signal and expose thylakoid signal...
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Protein Transport to the Outer Chloroplast Membrane01:11

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Chloroplast outer membrane proteins encoded by the nucleus are synthesized in the cytosol. Soon after synthesis, they bind cytosolic factors such as 14-3-3 protein and the Hsp70 chaperones that keep these precursors in an unfolded state until their translocation.
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Protein Transport to the Inner Chloroplast Membrane01:18

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Proteins targeted to the inner chloroplast membrane, or plastid proteins, are transported by two general pathways: the stop-transfer and the re-insertion or post-import pathways. Most plastid proteins carry N-terminal transit sequences and internal import sequences targeting it to the specific chloroplast subcompartment. Proteins targeted by the stop-transfer pathway have internal hydrophobic sequences that inhibit their translocation into the stroma. As a result, these precursors are arrested...
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The ADP/ATP Carrier Protein01:42

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ADP/ATP carrier or AAC protein is the most abundant carrier protein in the inner mitochondrial membrane. It transports large quantities of ADP and ATP, equivalent to the average human body weight, every day. Among other transporters, ACC protein is one of the best-studied members of the mitochondrial carrier protein family. The ADP/ATP carrier protein comprises two transmembrane helices connected to a loop and a single alpha-helix on the matrix side. It switches between two conformational...
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Protein Transport to the Stroma01:24

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Chloroplasts are triple membrane structures with an outer membrane, an inner membrane, and a thylakoid membrane, each containing distinct metabolite transporters, membrane translocons, and enzymes. Appropriate sorting and translocating these proteins to their correct membrane systems is essential for chloroplast function.
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Tail-anchoring of Proteins in the ER Membrane01:45

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Tail-anchored, or TA, proteins are estimated to make up to 3-5% of membrane proteins found in the eukaryotic cell. Such proteins have a single transmembrane domain located approximately 30 amino acid residues upstream from the C-terminal end. As a result, the signal recognition particle (SRP) cannot guide a TA protein to the ER membrane for cotranslational insertion. Hence, they are integrated into the ER membrane post-translationally using their C-terminal end as the anchor. TA proteins...
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Related Experiment Video

Updated: Oct 19, 2025

Affinity Purification of Chloroplast Translocon Protein Complexes Using the TAP Tag
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α-Tocopherol transfer protein (α-TTP).

Hiroyuki Arai1, Nozomu Kono2

  • 1Laboratory of Microenvironmental and Metabolic Health Science, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.

Free Radical Biology & Medicine
|September 26, 2021
PubMed
Summary

Alpha-tocopherol transfer protein (α-TTP) is crucial for vitamin E transport in the liver, regulating plasma α-tocopherol levels. Mutations in the α-TTP gene cause vitamin E deficiency disorders.

Keywords:
Ataxia with vitamin E deficiency (AVED)Intracellular lipid transportVitamin Eα-Tocopherolα-Tocopherol transfer protein

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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.