March 27 Flashcards
(12 cards)
How is mTOR kept in active conformation?
The FAT domain stabilizes the activation loop, keeps active conformation
How does rapamycin and the FKPB12 that it binds to work on TOR to have what outcome?
Need FKPB12 binding to have effect, gain of function. This complex binds where SK61 binds. This means that SK61 can’t be recruited and therefore phosphorylated, limiting cell growth. There is leucine 396 that is in the FRB pocket that helps form Hphobic pocket for substrate binding.
What does PRAS40 do to FRB substrate-recruitment site? What does it use to bind, is this motif similar in other things that bind to FRB site?
It also binds to the FRB site, also where the rapamycin-FKBP12 complex and the substrate S6K1 bind.
PRAS40 has 5 key Hphobic AAs that binds very strongly in Hphobic pocket. This motif is similar to one in the substrate S6K1 and the other substrate 4EBP1. This is called TOS motif
How does RAPTOR help in substrate recruitment?
RAPTOR binds the TOS motif of substrates, then passes substrates to FRB?
How does GTP-Rheb activate mTORC1?
It binds to the N and M heat repeats. Rheb is a GTPase, it has 2 switches, small regions that interact with the HEAT repeats.
- Binding to HEAT repeats causes huge movement of these repeats
- N-terminal of Heat repeat (N-HEAT) moves around FAT hinge, moves the FAT clamp
- ATP on N-lobe of kinase is now free to move closer to C-lobe residues that have the needed residues
Get 900 fold activation
Are cancer expected to have less or more active TOR due to mutations lowering energy barrier for the protein to be in active conformation
More
What 2 molecules regulate mTOR activity?
Rheb and Rag GTPases. Rheb is GTP bound on lysosome surface when high ATP. Only when Rag is activated by nutrient availability is mTORC1 recruited from cytoplasm to lysosome.
What is the GAP (GTPase activating protein) for Rheb?
It is TSC. If TSC is inactivated, it is not at the lysosome anymore to keep Rheb inactivated, so Rheb can now be active and activate mTORC1
Is the AMPK pathway dominant or not over the amounts of AA’s or other factors?
AMPK is dominant, it will PO4 RAPTOR (direct) and activate TSC2 (indirect). Both will keep mTOR1 inactive either directly or indirectly by keeping Rheb GDP bound.
What AA’s are aboslutely required for mTORC1 activation? Why?
Leucine and Arginine. Rag GTPases, 4 of them in mammals, A to D. AAs promote RagB binding to GTP, so now they activate mTORC1 via RAPTOR.
How do Rag heterodimers form?
4 Types, ABC and D. It is hetero dimer with either Rag A or B, attached to C or D.
