Protein trafficking 2 Flashcards
Difference between cleaved and uncleaved signals
If cleaved -> nuclear import
uncleaved 0> mitochondrial / E.R. import
To cross the lipid bilayer:
- Nuclear pore: small proteins <5kd + larger proteins have to make contact active transport mech.
- Receptor - some proteins are guided to channels and bound to soluble/ insoluble receptors
Nucleus signal sequence
Positive string of aa + signal patch is positively charged
Nucleoporins
Proteins that make up nuclear pore complexes
Nuclear import occurs after
translation - fully folded
Nuclear import + export general steps:
- NLS -> importin -> FG repeats serve as binding sites
2. Export double leucine signal -> bind to export mech. -> exportin
How does Ron-GTP influence the import process?
- Importin + protein complex -> protein is displaced by Ron-GTP
- Importin + Ron-GTP to cytosol
- Ron-GTP dissociates + hydrolyses in cytoplasm
How does Ron-GTP influence the export process?
- Ron-GTP + protein + exportin -> 3 way xomplex
- Out by FG repeats
- GTP -> GDP breaks complex apart
- > exportin can be taken back
Mitochondrial export overview
- Post-translational + unfolded
- 99% of all proteins unpaired
- makes 13 only
Shape of signal sequence
Amphiphatic alpha helix
Enter into mitochondria mech
- SS binds tom complex once recognised
- Protein into Tom
- If matrix protein then goes through Tim
- Signal cleaved by peptidase
- Folds
How does Hsp 70 contribute to mitochondrial imports?
Cytosolic Hsp70 keeps the import unfolded -> uses ATP to prevent folding
-> dissociated once into m
Why is ATP needed?
Translocation of proteins
How does mitochondrial hsp70 contribute to import process?
Binds at Tim and stops slide back, pulling protein into mitochondrea
What does mitochondrial hsp60 do?
Helps translocated protein fold
