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Literature summary for 7.4.2.4 extracted from
- Molecular chaperone involvement in chloroplast protein import (2013), Biochim. Biophys. Acta, 1833, 332-340.
Localization
| Localization | Comment | Organism | GeneOntology No. | Textmining |
|---|---|---|---|---|
| chloroplast | in chloroplasts, Hsp93 can form part of the Clp protease complex (in a second role, additional to that in preprotein import), which recognizes and unfolds substrate proteins that are destined for degradation. Interaction of Hsp93 with the proteolytic ClpP core is ATP dependent | Arabidopsis thaliana | 9507 | - |
| chloroplast stroma | associated to the membrane channel of the inner envelope membrane, at the stromal side | Arabidopsis thaliana | 9570 | - |
Metals/Ions
| Metals/Ions | Comment | Organism | Structure |
|---|---|---|---|
| Mg2+ | required | Arabidopsis thaliana |  |
Molecular Weight [Da]
| Molecular Weight [Da] | Molecular Weight Maximum [Da] | Comment | Organism |
|---|---|---|---|
| 200000 | - |
dimeric Hsp93-V/ClpC1 isoform | Arabidopsis thaliana |
Natural Substrates/ Products (Substrates)
| Natural Substrates | Organism | Comment (Nat. Sub.) | Natural Products | Comment (Nat. Pro.) | Rev. | Reac. |
|---|---|---|---|---|---|---|
| ATP + H2O | Arabidopsis thaliana | - |
ADP + phosphate | - |
? | |
Organism
| Organism | UniProt | Comment | Textmining |
|---|---|---|---|
| Arabidopsis thaliana | Q9FI56 | isozyme Hsp93-V; isoform Hsp93-V or ClpC1 | - |
| Arabidopsis thaliana | Q9SXJ7 | isozyme Hsp93-III; isoform Hsp93-III or ClpC2 | - |
Source Tissue
| Source Tissue | Comment | Organism | Textmining |
|---|---|---|---|
| leaf | - |
Arabidopsis thaliana | - |
| additional information | the expression of isozyme Hsp93-V is much higher than that of isozyme Hsp93-III | Arabidopsis thaliana | - |
Substrates and Products (Substrate)
| Substrates | Comment Substrates | Organism | Products | Comment (Products) | Rev. | Reac. |
|---|---|---|---|---|---|---|
| ATP + H2O | - |
Arabidopsis thaliana | ADP + phosphate | - |
? | |
Subunits
| Subunits | Comment | Organism |
|---|---|---|
| dimer | Hsp93-V/ClpC1 isoform | Arabidopsis thaliana |
| hexamer | recombinant Hsp93-III/ClpC2 isozyme in solution is in dimeric form, upon addition of ATP, the hexamer state is observed. TIC-associated Hsp93 may act as a hexamer | Arabidopsis thaliana |
Synonyms
| Synonyms | Comment | Organism |
|---|---|---|
| hsp93 | - |
Arabidopsis thaliana |
| Hsp93-III | - |
Arabidopsis thaliana |
| Hsp93-V | - |
Arabidopsis thaliana |
General Information
| General Information | Comment | Organism |
|---|---|---|
| evolution | Hsp93/ClpC is a member of the Hsp100 family of chaperones, which itself belongs to the broader AAA+ (ATPases associated with various cellular activities) superfamily. Hsp100 proteins contain one or two AAA+ domains, and typically assemble into hexameric rings with a central pore through which substrate proteins can be threaded. Hsp100 proteins mediate ATP-dependent unfolding of proteins, in processes linked to protein degradation, protein disassembly, or protein trafficking across membranes | Arabidopsis thaliana |
| malfunction | Arabidopsis hsp93-V knockout plants are pale, with underdeveloped chloroplasts containing fewer thylakoid membranes and displaying reduced protein import efficiency. In contrast, hsp93-III knockout mutants are indistinguishable from wild-type. This can be explained by redundancy, as hsp93-III hsp93-V double mutants are embryo lethal and overexpression of Hsp93-III can complement hsp93-V, suggesting that the two isozyme proteins have overlapping functions and are able to partially substitute for each other in the single mutants | Arabidopsis thaliana |
| metabolism | several chaperones and cochaperones mediate different stages of chloroplast import of preproteins, which are in a largely unfolded state. Cytosolic factors such as Hsp90, Hsp70 and 14-3-3 may assist preproteins to reach the TOC complex, i.e. translocon at the outer envelope membrane of chloroplasts complex, at the chloroplast surface, preventing their aggregation or degradation. Chaperones may also be involved in the intermembrane space transport. Preprotein translocation is completed at the trans side of the inner membrane by ATP-driven motor complexes. A stromal Hsp100-type chaperone, Hsp93, cooperates with Tic110 and Tic40 in one such motor complex, while stromal Hsp70, EC 3.6.4.10, is proposed to act in a second, parallel complex. Upon arrival in the stroma, chaperones (e.g., Hsp70, Cpn60, cpSRP43) also contribute to the folding, assembly or onward intraorganellar guidance of the proteins. Chaperone involvement in the stroma during chloroplast protein import, modeling, detailed overview | Arabidopsis thaliana |
| physiological function | the enzyme is involved in preprotein import into chloroplasts as a chaperone. Additionally, in chloroplasts, Hsp93 can form part of the Clp protease complex, which recognizes and unfolds substrate proteins that are destined for degradation. Interaction of Hsp93 with the proteolytic ClpP core is ATP dependent. The Tic110-Tic40 (Tic = translocon at the inner envelope membrane of chloroplasts) interaction triggers the release of the transit peptide from Tic110 and enables the association of the preprotein with Hsp93. Tic110 may dissociate from Tic40 when there is no transit peptide bound. The Tic40 Sti1 domain then stimulates ATP hydrolysis by Hsp93, which acts to pull the preprotein into the stroma using the released energy. Subsequently, Hsp93-ADP may dissociate from Tic40. TIC-associated hexameric Hsp93 may act by threading incoming preproteins through the axial channel of the complex. Hsp93/ClpC acts as a regulatory chaperone in the Clp protease, the Clp protease is essential for chloroplast development and plant viability | Arabidopsis thaliana |
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