Protein Sorting and Targeting Flashcards
GEF and GAPS in import/export, basic idea
- GEFS switch out GDP for GTP as the protein enters the nucleus; turns them ON
- GAPS hydrolyze GTP as they leave the nucleus…the GAPS are associated with the filaments on the NPC ; turns them OFF
Nuclear Export story (3 basic steps)
- Cargo protein with NES, and binds to exportin and Ran GTP
- Pass through NPC via interaction w/nucleoporins
- GAP, associated with cytoplasmic filaments,
Story of mitochondria import? Where does the energy come from?
- Hsc70 binds and unfolds the protein with the MTS via ATP HYDROLYSIS
- MTS binds the TOM receptor on OMM
- TOM transfers protein to TOM40 translocator
- TOM40 and TIM interact which brings OMM and IMM together
- Protein then travels through both translocators into matrix
- MTS is cleaved by matrix processing protease
- matrix chaperone HSC70 refold the protein via ATP hydrolysis
Story of protein going to RER, 5 steps.
- SRP binds ER signal sequence (amino acids) and large ribosomal subunit
- Binds to SRP receptor on RER membrane and together, they bind GTP creating a GTP-ase
- GTP hydrolyzed, translocon is opened and protein complex transferred to it, and SRP dissociates.
- signal peptidase in ER lumen cleaves the ERSS.
- Ribosome completes synthesis, translocon closes
With Type 1 ER membrane proteins, what happens? what signal is used?
- stop transfer anchor sequence is translated as ribosome translates protein into the lumen.
- The ribosome then stops translation, and transfers protein into the membrane.
- ribosome finishes synthesis in cytoplasm. COO- ends up in cytosol.
4.
Formation of vessicle requires
vSNARE and tSNARE proteins, the coat proteins COP II – ER to Golgi and COP I – Retrograde transport, Clathrin – Golgi to endosomes & endocytosis, and ARF which is the G-protein for COP I and Clathrin vesicles; or Sar1which is the G-protein for COP II vesicles
story of vessicle formation (5 steps)
- Sar1 binds to ER protein Sec12 which functions as a GEF, so GDP is exchanged for GTP, and turns on
- Sar1 inserts into membrane, which allows COPII to form, and the vessicle buds.
- COPII act as GAPs, which hydrolyze the GTP, and the coat dissassembles.
- vessicle travels to golgi
- Rab GTPases control the docking of vesicles to the target membrane, where vSNARE then binds to tSNARE in target membrane, resulting in membrane fusion
What do ER-resident proteins do? what signal do they have?
they allow for retrograde transport if a mistake is made. Have KDEL signal.
Difference in the conformation of proteins traveling into nucleus vs. those traveling into ER or mitochondria?
Proteins can be folded and travel into nucleus… in the others, they are unfolded.
Which Ran binds to their karyopherin when entering/exiting the nucleus?
Ran GTP binds to exportin to leave the nucleus. Ran GDP does NOT bind to importin to enter…
Difference between alpha importin and beta importin? how do the importins interact with nucleoporins?
alpha importin binds to NLS. Beta importin mostly just binds to alpha importin. They interact with with nucleoporins via hydrophobic interactions.
Nuclear import story, 4 steps.
- Importin binds to protein w/NLS, and moves into the nucleus, at the same time Ran GDP goes into nucleus separately
- The complex then interacts with Ran GTP, and protein is released into nucleus
- The left over importin-Ran GTP complex moves into cytoplasm
- GAP interacts with it as it leaves the NPC, forming Ran GDP which dissociates from the importin
Type II integral membrane proteins work how? What signal?
- signal anchor sequence located internally, which was translated on free ribosome in cytosol.
- SRP binds it, and then binds to SRPR on membrane.
- GTP is hydrolyzed, protein goes to membrane
- translation finished, with carboxy end ending up in the LUMEN!
* translocon stays open the whole time for type II
proteins destined for endosome or lysosome need what?
Clathrin-coated vesicles, which require AP adaptor proteins to assist in forming clathrin-coated vessicle. also require dynamin which uses GTP to help vesicle bud off membrane.
