Related Experiment Video
Updated: May 23, 2026
06:29
Studying Protein Import into Chloroplasts Using Protoplasts
Published on: December 10, 2018
Molecular chaperone involvement in chloroplast protein import
Úrsula Flores-Pérez1, Paul Jarvis
1Department of Biology, University of Leicester, Leicester LE1 7RH, UK.
Biochimica Et Biophysica Acta
|April 24, 2012
Summary
Chaperones assist in the crucial process of transporting proteins into chloroplasts, ensuring proper function and cellular health in plants. This review details chaperone roles in protein import across the chloroplast envelope.
Area of Science:
- Plant Biology
- Cell Biology
- Biochemistry
Background:
- Chloroplasts, organelles of endosymbiotic origin, are vital for plant functions.
- Most chloroplast proteins are nucleus-encoded and require post-translational import.
- Protein import involves navigating multiple cellular compartments via TOC and TIC complexes.
Purpose of the Study:
- To review the involvement of chaperones in preprotein translocation across the chloroplast envelope.
- To highlight the mechanisms and key players in chloroplast protein import.
- To discuss the role of chaperones in protein folding and intraorganellar guidance.
Main Methods:
- Literature review focusing on chaperone involvement in chloroplast protein import.
- Analysis of existing research on protein translocation machinery (TOC/TIC).
- Examination of the roles of various chaperone families (Hsp90, Hsp70, Hsp100, etc.).
Main Results:
- Cytosolic chaperones (Hsp90, Hsp70, 14-3-3) facilitate preprotein targeting to the TOC complex.
- Stromal chaperones (Hsp93, Hsp70) are involved in ATP-driven translocation across the inner membrane.
- Post-translocation chaperones (Hsp70, Cpn60, cpSRP43) aid in folding and intraorganellar trafficking.
Conclusions:
- Chaperones play critical, multifaceted roles throughout the chloroplast protein import pathway.
- Understanding chaperone involvement is key to comprehending chloroplast biogenesis and function.
- This review consolidates current knowledge on chaperone-mediated protein import into chloroplasts.
Related Concept Videos
01:18Protein 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...
01:24Protein 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 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...
01:11Protein 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.
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.
01:22Protein 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...
03:00Molecular Chaperones and Protein Folding
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...
The...
03:00Molecular Chaperones and Protein Folding
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...
The...