Topic
Toc complex
About: Toc complex is a research topic. Over the lifetime, 76 publications have been published within this topic receiving 5151 citations.
Papers published on a yearly basis
Papers
TL;DR: It is shown that Arabidopsis thaliana Toc159 (atToc159) is essential for the biogenesis of chloroplasts, and two proteins that are related to atToc 159 probably help to maintain basal protein import in ppi2, and so constitute components of alternative, atTOC159-independent import pathways.
Abstract: Light triggers the developmental programme in plants that leads to the production of photosynthetically active chloroplasts from non-photosynthetic proplastids. During this chloroplast biogenesis, the photosynthetic apparatus is rapidly assembled, mostly from nuclear-encoded imported proteins, which are synthesized in the cytosol as precursors with cleavable amino-terminal targeting sequences called transit sequences. Protein translocon complexes at the outer (Toc complex) and inner (Tic complex) envelope membranes recognize these transit sequences, leading to the precursors being imported. The Toc complex in the pea consists of three major components, Toc75, Toc34 and Toc159 (formerly termed Toc86). Toc159, which is an integral membrane GTPase, functions as a transit-sequence receptor. Here we show that Arabidopsis thaliana Toc159 (atToc159) is essential for the biogenesis of chloroplasts. In an Arabidopsis mutant (ppi2) that lacks atToc159, photosynthetic proteins that are normally abundant are transcriptionally repressed, and are found in much smaller amounts in the plastids, although ppi2 does not affect either the expression or the import of less abundant non-photosynthetic plastid proteins. These findings indicate that atToc159 is required for the quantitative import of photosynthetic proteins. Two proteins that are related to atToc159 (atToc120 and atToc132) probably help to maintain basal protein import in ppi2, and so constitute components of alternative, atToc159-independent import pathways.
402 citations
TL;DR: The protein translocon of the outer envelope of chloroplasts (Toc) consists of the core subunits Toc159, Toc75, and Toc34, and the core complex was purified to investigate the molecular structure.
Abstract: The protein translocon of the outer envelope of chloroplasts (Toc) consists of the core subunits Toc159, Toc75, and Toc34. To investigate the molecular structure, the core complex was purified. This core complex has an apparent molecular mass of ∼500 kD and a molecular stoichiometry of 1:4:4–5 between Toc159, Toc75, and Toc34. The isolated translocon recognizes both transit sequences and precursor proteins in a GTP-dependent manner, suggesting its functional integrity. The complex is embedded by the lipids phosphatidylcholine and digalactosyldiacylglyceride. Two-dimensional structural analysis by EM revealed roughly circular particles consistent with the formation of a stable core complex. The particles show a diameter of ∼130 A with a solid ring and a less dense interior structure. A three-dimensional map obtained by random conical tilt reconstruction of electron micrographs suggests that a “finger”-like central region separates four curved translocation channels within one complex.
238 citations
TL;DR: A constitutively expressed homologue hsc 70 as part of a membrane complex which still contained the precursor protein and a second protein of 86 kDa molecular weight from the outer envelope membrane was also identified as a major component of this complex.
Abstract: Isolated outer envelope membrane from pea (Pisum
sativum L.) chloroplasts can be used in vitro to study
binding and partial translocation of precursor proteins
destined for the inside of the organelle. Efficient binding
to a receptor protein on the outside of the membrane
vesicle and generation of a translocation intermediate
depends strictly on the presence of ATP. Protease
treatment of the translocation intermediate demonstrates
its insertion into the membrane. The membraneinserted
precursor protein cannot be extracted by 1 M
NaCl and is also NaOH resistant to a large extent. Mild
solubilization of outer envelope membranes by detergent
resulted in the isolation of a complex which still
contained the precursor protein. We have identified a
constitutively expressed homologue hsc 70 as part of
this membrane complex. Antibodies against hsp 70
(inducible heat shock protein 70) were able to immunoprecipitate
the complex bound precursor protein.
A second protein of 86 kDa molecular weight (OEP 86)
from the outer envelope membrane was also identified
as a major component of this complex.
208 citations
TL;DR: It is proposed that Toc64 functions early in preprotein translocation, maybe as a docking protein for cytosolic cofactors of the protein import into chloroplasts.
Abstract: A subunit of the preprotein translocon of the outer envelope of chloroplasts (Toc complex) of 64 kD is described, Toc64. Toc64 copurifies on sucrose density gradients with the isolated Toc complex. Furthermore, it can be cross-linked in intact chloroplasts to a high molecular weight complex containing both Toc and Tic subunits and a precursor protein. The 0 A cross-linker CuCl2 yields the reversible formation of disulfide bridge(s) between Toc64 and the established Toc complex subunits in purified outer envelope membranes. Toc64 contains three tetratricopeptide repeat motifs that are exposed at the chloroplast cytosol interface. We propose that Toc64 functions early in preprotein translocation, maybe as a docking protein for cytosolic cofactors of the protein import into chloroplasts.
178 citations
TL;DR: A model of differential presequence recognition by Toc34 and Toc159 is developed and it is confirmed that the receptor form of Toc 159 is integrated into the membrane.
Abstract: The Toc core complex consists of the pore-forming Toc75 and the GTPases Toc159 and Toc34. We confirm that the receptor form of Toc159 is integrated into the membrane. The association of Toc34 to Toc75/Toc159 is GTP dependent and enhanced by preprotein interaction. The N-terminal half of the pSSU transit peptide interacts with high affinity with Toc159, whereas the C-terminal part stimulates its GTP hydrolysis. The phosphorylated C-terminal peptide of pSSU interacts strongly with Toc34 and therefore inhibits binding and translocation of pSSU into Toc proteoliposomes. In contrast, Toc159 recognises only the dephosphorylated forms. The N-terminal part of the pSSU presequence does not influence binding to the Toc complex, but is able to block import into proteoliposomes through its interaction with Toc159. We developed a model of differential presequence recognition by Toc34 and Toc159.
154 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2021 | 1 |
| 2020 | 2 |
| 2019 | 1 |
| 2018 | 1 |
| 2017 | 2 |
| 2016 | 1 |