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Related Concept Videos

Protein Transport to the Inner Chloroplast Membrane01:18

Protein Transport to the Inner Chloroplast Membrane

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...
Protein Transport to the Outer Chloroplast Membrane01:11

Protein Transport to the Outer Chloroplast Membrane

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.
Two models describe the mechanism of precursor recognition and entry across the outer membrane through the TOC complex. Model 1 suggests the newly synthesized precursor binds to the TOC receptor 159 and forms a complex.
Protein Transport to the Stroma01:24

Protein Transport to the Stroma

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.
Protein complexes called the translocon of the outer chloroplast membrane or TOC complex, and the translocon of the inner chloroplast membrane or TIC complex mediate the...
Protein Transport to the Thylakoids01:22

Protein Transport to the Thylakoids

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...
Overview of Protein Sorting and Transport01:45

Overview of Protein Sorting and Transport

Eukaryotic cells have different membrane-bound organelles with distinct protein requirements. The process by which proteins are targeted to a specific organelle is called protein sorting.
Protein sorting can be of two types: signal-based sorting and vesicle-based trafficking. In signal-based sorting, specific amino acid sequences called sorting signals target proteins to the proper location inside the cell either via gated transport or by protein translocation.  In gated transport, folded...
Transport Across the Golgi01:26

Transport Across the Golgi

While it is unclear how molecules move between adjacent Golgi cisternae, it is apparent that the molecules move from cis- cisterna, the entry face, to the trans- cisterna, the exit face. Experiments initially suggested vesicles that bud from one cisterna and fuse with the next cisterna to transport proteins between the cisternae. This vesicular transport model describes the Golgi apparatus as a relatively static structure with a unique enzyme composition in each cisterna. Molecules are...

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Related Experiment Video

Updated: May 10, 2026

Studying Protein Import into Chloroplasts Using Protoplasts
06:29

Studying Protein Import into Chloroplasts Using Protoplasts

Published on: December 10, 2018

Evidence for glycoprotein transport into complex plastids.

Madeleine Peschke1, Daniel Moog, Andreas Klingl

  • 1Department of Cell Biology of the Philipps University, 35032 Marburg, Germany.

Proceedings of the National Academy of Sciences of the United States of America
|June 12, 2013
PubMed
Summary

This study shows that N-glycosylation occurs during protein transport into diatom complex plastids. This finding complicates our understanding of how proteins cross the four membranes of these organelles.

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Last Updated: May 10, 2026

Studying Protein Import into Chloroplasts Using Protoplasts
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Published on: December 10, 2018

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Isolation of Physiologically Active Thylakoids and Their Use in Energy-Dependent Protein Transport Assays
12:25

Isolation of Physiologically Active Thylakoids and Their Use in Energy-Dependent Protein Transport Assays

Published on: September 28, 2018

Area of Science:

  • * Cell biology
  • * Algal biology
  • * Protein transport

Background:

  • * Diatom complex plastids evolved via secondary endosymbiosis and have four surrounding membranes.
  • * Nucleus-encoded proteins must cross all four membranes, posing transport challenges.
  • * The presence of glycoproteins in complex plastids adds complexity to protein translocation.

Purpose of the Study:

  • * To investigate N-glycosylation of proteins during transport into diatom complex plastids.
  • * To identify endogenous glycoproteins within diatom complex plastids.
  • * To explore the implications of N-glycosylation for protein translocation across multiple membranes.

Main Methods:

  • * Generation of reporter proteins with artificial N-glycosylation sites.
  • * Analysis of protein glycosylation during transport into the complex plastid of *Phaeodactylum tricornutum*.
  • * Identification of endogenous glycoproteins within different plastid compartments.

Main Results:

  • * Plastidal reporter proteins with artificial N-glycosylation sites were successfully glycosylated during import.
  • * Five endogenous glycoproteins were identified and localized to various compartments of the complex plastid.
  • * N-glycosylation occurs at the outermost membrane, with subsequent translocation across inner membranes for stromal proteins.

Conclusions:

  • * N-glycosylation is an important post-translational modification during protein import into diatom complex plastids.
  • * The findings challenge existing models of protein translocation across the four-membrane envelope.
  • * This study raises new questions about the function and regulation of transport machineries like Toc/Tic translocons.