found in all 3 domains (but not universal) couloo expoass Dnak (Hsp70, Bip) teams with DnaJ (Hsp40) and GrpE (Bag1, HspBP1) nucleotide exchange factor po VLL PROGE displays non-specific binding to short (~7 AA) unstructured hydrophobic regions of peptides shields nascent polypeptides as emerge from ribosome Die (~22% of total proteins in cell) and dissociate protein- DLOIS protein interactions after translation DnaK-DnaJ-GrpE Chaperone Team OGUCL In ATP-dependent mechanism, binds & releases proteins in unfolded state which either spontaneously fold or are errebound by chaperones
The Correct Answer and Explanation is:
Sure! The correct answer here relates to the DnaK-DnaJ-GrpE chaperone system and its role in protein folding.
Correct Answer:
DnaK-DnaJ-GrpE chaperone team
Explanation (300+ words):
The DnaK-DnaJ-GrpE system is a well-characterized molecular chaperone machinery primarily found in bacteria (like E. coli) but homologous systems exist in all three domains of life: Bacteria, Archaea, and Eukarya, although the exact proteins and co-factors can differ slightly. This system is not universal (not found in every organism identically) but is highly conserved across many species, reflecting its critical role in maintaining cellular protein homeostasis.
Components and Mechanism:
- DnaK is a member of the Hsp70 family of heat shock proteins (chaperones). It binds unfolded or partially folded proteins through exposed hydrophobic regions. These hydrophobic patches typically consist of short (~7 amino acids) unstructured regions on nascent or misfolded polypeptides that need to be shielded to prevent aggregation.
- DnaJ (also known as Hsp40) acts as a co-chaperone that stimulates the ATPase activity of DnaK. By binding to client proteins first, DnaJ delivers them to DnaK and enhances DnaK’s affinity for the substrate.
- GrpE serves as a nucleotide exchange factor (NEF), facilitating the release of ADP from DnaK, allowing ATP to bind again, which leads to substrate release.
The chaperone team functions in an ATP-dependent cycle:
- ATP-bound DnaK has low affinity for substrate proteins.
- Upon ATP hydrolysis, stimulated by DnaJ, DnaK tightly binds to the unfolded protein.
- GrpE promotes nucleotide exchange, replacing ADP with ATP, causing DnaK to release the folded or partially folded client.
- This cycle repeats as needed until the protein achieves its correct native conformation or is transferred to other chaperones.
Role in Protein Folding and Cellular Health:
In sum, the DnaK-DnaJ-GrpE system is a crucial ATP-dependent chaperone team that ensures proteins fold properly by selectively binding and releasing unfolded polypeptides through coordinated ATP hydrolysis and nucleotide exchange. Its conservation across all three domains, albeit with variations, highlights its fundamental role in protein quality control.
If you want, I can also provide specific examples or analogies to help understand the system better!