EC Number   |
General Information |
Reference |
|---|
   7.4.2.4 | 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 |
733398 |
| 7.4.2.4 | 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 |
733398 |
| 7.4.2.4 | malfunction |
cpSecA absence can lead to severe defects in chloroplast sub-organelle structure and function |
734384 |
| 7.4.2.4 | malfunction |
silencing of SCY2 and SCY1 results in chlorotic cotyledons. Null mutants of SCY2 in Arabidopsis (Arabidopsis thaliana) exhibit a severe embryo-lethal phenotype |
751878 |
| 7.4.2.4 | 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 |
733398 |
| 7.4.2.4 | metabolism |
the SEC2 translocase likely integrates a subset of inner envelope membrane proteins, such as FTSH12 and TIC40 |
751878 |
| 7.4.2.4 | metabolism |
two further pathways are used to translocate lumenal proteins across the thylakoid membrane from the stroma and, again, the two pathways differ dramatically from each other. One is a Sec-type pathway, in which ATP hydrolysis by SecA drives the transport of the substrate protein through the membrane in an unfolded conformation. The other is the twin-arginine translocation (Tat) pathway, where substrate proteins are transported in a folded state using a unique mechanism that harnesses the proton motive force across the thylakoid membrane. cpSecY and cpSecA work in concer in the Sec-type pathway. Targeting of proteins to the chloroplast thylakoid lumen, overview |
734384 |
| 7.4.2.4 | physiological function |
AtcpSecA plays an essential role in chloroplast biogenesis, structure and function, the absence of which triggers a retrograde signalling (chloroplast-to-mitochondrion) possibly leads to reprogramming of chloroplast and mitochondrion gene expression to alleviate photooxidative stress in order to survive with an insufficient energy supply |
712609 |
| 7.4.2.4 | physiological function |
SCY2 plays an essential role in chloroplast biogenesis beyond embryo development |
751878 |
| 7.4.2.4 | physiological function |
the amount of nuclear-encoded SecA protein increases almost 4fold with increase in temperature, while the amount of plastid-encoded SecA protein increases only slightly. Data suggest an important role of nuclear-encoded SecA protein at high temperature |
719126 |
