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Related Concept Videos

Molecular Chaperones and Protein Folding03:00

Molecular Chaperones and Protein Folding

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The native conformation of a protein is formed by interactions between the side chains of its constituent amino acids. When the amino acids cannot form these interactions, the protein cannot fold by itself and needs chaperones. Notably, chaperones do not relay any additional information required for the folding of polypeptides; the native conformation of a protein is determined solely by its amino acid sequence. Chaperones catalyze protein folding without being a part of the folded protein.
The...
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Molecular Chaperones and Protein Folding03:00

Molecular Chaperones and Protein Folding

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Protein Transport to the Inner Chloroplast Membrane01:18

Protein Transport to the Inner Chloroplast Membrane

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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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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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Protein Transport to the Outer Chloroplast Membrane01:11

Protein Transport to the Outer Chloroplast Membrane

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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 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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In Situ Monitoring of Transiently Formed Molecular Chaperone Assemblies in Bacteria, Yeast, and Human Cells
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Protomer Roles in Chloroplast Chaperonin Assembly and Function.

Cuicui Bai1, Peng Guo1, Qian Zhao1

  • 1State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China; University of Chinese Academy of Sciences, Beijing 100101, China.

Molecular Plant
|June 10, 2015
PubMed
Summary

This study reveals that the chloroplast chaperonin CPN60 complex in Chlamydomonas reinhardtii requires all three protomers (CPN60α, CPN60β1, CPN60β2) for function. The CPN60α subunit is essential for autotrophic growth and proper complex assembly.

Keywords:
Cpn60assemblychaperoninphotosynthesisprotomer

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Analysis of Protein Import into Chloroplasts Isolated from Stressed Plants
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Analysis of Protein Import into Chloroplasts Isolated from Stressed Plants
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Area of Science:

  • Plant molecular biology
  • Protein biochemistry
  • Chaperone systems

Background:

  • Chloroplasts contain CPN60 chaperonins crucial for protein folding.
  • The specific roles of CPN60α, CPN60β1, and CPN60β2 subunits and their assembly remain unclear.

Purpose of the Study:

  • To investigate the individual roles of CPN60α, CPN60β1, and CPN60β2 subunits.
  • To determine how these protomers assemble into functional chaperonin complexes in Chlamydomonas reinhardtii.

Main Methods:

  • Protein complex identification and co-expression in Escherichia coli.
  • Oligomerization analysis and molecular weight determination.
  • In vitro reconstitution assays with ATP hydrolysis.
  • Functional complementation assays in E. coli and gene down-regulation in Chlamydomonas.

Main Results:

  • Identified hetero-oligomeric CPN60 complexes containing CPN60α, CPN60β1, and CPN60β2.
  • Demonstrated ATP-dependent dynamic assembly and disassembly of CPN60 oligomers.
  • Showed that only the hetero-oligomeric CPN60αβ1β2 complex functionally cooperates with GroES.
  • Confirmed CPN60α subunit is essential for autotrophic growth in Chlamydomonas.

Conclusions:

  • The functional chloroplast chaperonin complex requires a specific hetero-oligomeric assembly of CPN60α, CPN60β1, and CPN60β2 subunits.
  • CPN60α plays a critical in vivo role, essential for growth and autotrophic capability.
  • Chaperonin complex assembly and dynamics are regulated by ATP hydrolysis.