Lecture 9 Flashcards
BiP
HSP70 in the ER
DNAJ
Assists folding with BiP (co-chaperone)
Sec63?
TM DNAJ protein that interacts with BIP and brings it close to the translocon
-Does not interact with the nascent peptide
Thioredexins?
-Chaperones that guide the formation of disulfide bonds in the ER
-Break improperly fromed disulfide bonds and reforms them
Two types of Thioredexins?
1.Protein disulfide isomerase ( brings two cysteines close together)
2. ERp57
How does PDI promote disulfide bonding?
- PDI has its own two cysteines which will engage in disulfide bonding with the cysteines of the nascent chain
- Oxidized PDI catalyzes the formation of disulfide bonds in cysteines and then PDI becomes reduced
Without PDI?
Cysteines would make disulfide bonds with the wrong cysteines
PDI Regeneration?
- PDI becomes reduced by oxidizing the susbtrate
- Ero1 reoxidizes the PDI and becomes reduced with FAD
- Ero1 is oxidized again by FAD
- FAD is oxdized by O2
Occurs in the ER
Proteins that regulate the addition of the N-linked glycosyslation?
Calnexin
Calreticulin
CNX vs CRT?
CNX: Has TM helix attached into the membrane of the ER (interacts with proteins around the ER membrane)
CRT: Found in the lumen of the ER (interacts with proteins floating in the ER)
CNX and CRT interact with?
Thioredoxin ERp57 and the glycan added
Immature protein of the ER?
Contains one mannose and three glucose
CNX and CRT binding?
Glucosidases in the lumen of the ER trim off the first and second glucose molecules. When the protein only has one glucose molecule this is when CNX and CRT bind. CNX recognizes if the protein is folded, if the. protein is still unfolded when CNX releases it the mannose sugars will be trimmed and the protein will be degraded
UGGT Cycle?
- CNX binds the protein in the Er with trimmed glucose.
- CNX also has thioredoxin which aids in disulfide bonding. CNX gives the protein time to fold.
- GLucose is then trimmed and the protein released
- If the protein is improperly folded (hydrophobic residues on exterior), UGGT will recognize the protein
- UGGT gives the glucose again so the protein can try folding again
CNX and CRT cycle?
- CRT binds to the protein with one glucose.
- CRT reacts with thioredoxin and aids in disulfide bonding
- CRT releases the protein and the final glucose is trimmed
4.IF protein is properly folded, all mannose are kept and protein goes to SP - IF protein is misfolded it is recognized by UGGT
UGGT competition?
-UGGT has competition with enzymes that want to remove the mannose sugars
-IF the mannose surgars are cut off the protein is recognized by EDEM and sent to be degraded
ERAD?
Degrades both lumenal and transmembrane proteins
ERAD substrates?
Misfolded proteins
Lectin
Recognizes a small amount of mannose on protein and targets the protein to the retro-translocon
Family of p97?
AAA ATPase
-Pulls peptide from the ER to the cytosol with the help of ATP hydrolysis
-Helps unfold the protein
UPR?
-Activated by the accumulation of unfolded proteins in the ER
- Transcription of ER chaperones, ERAD components increases (size of ER increases)
Persistent UPR?
-Cell must undergo aptosis
