Biology 2382B Lecture Notes - Lecture 6: Translocon, Atp Hydrolysis, Cell Membrane
5 May 2018
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Getting Proteins into Membranes
- As protein is translated in cytosol, ribosome hits Topogenic Sequences that tells it what to do w/the protein.
- Topogenic Sequences (hydrophobic):
- N-terminal signal sequence tells ribosome to go to ER (secreted protein)
- Stop Transfer Anchor sequence (STA) stops transfer and anchors protein into membrane
- Signal Anchor sequence (SA) tells ribosome to go to ER (internal, uncleaved sequence).
- C-terminus signal sequence
Tail-Anchored Proteins
- C-terminal domain in membrane and N-terminal domain
in cytoplasm (no extracellular domain).
- Ribosome encounters hydrophobic C-terminal tail and recruits Get3.
- Get3 gets the protein to the ER and membrane-embedded Get1 and
Get2 shove the protein into the plasma membrane using ATP hydrolysis.
Type 1 Transmembrane Proteins
- 2 topogenic sequences N-terminal and STA
- Ribosome encounters N-terminal signal sequence that is recognized by SRP
- SRP takes protein to ER and puts it through translocon.
- Ribosome translates in lumen but then encounters STA
- STA stop transferring into lumen, start transferring into cytosol
- N-terminus is in lumen, STA is transmembrane, C-terminus is in cytosol
Type 2 and 3 Transmembrane Proteins
- 1 topogenic sequence SA
- Ribosome encounters SA signal which tells it to go to ER and shoves it into lumen.
- If there are (+) AA between N-terminus and SA sequence, ribosome leaves N-terminus in cytosol, but C-terminus
goes into lumen (Type 2).
- If there are no (+) AA between N-terminus and SA sequence, ribosome shoves N-terminus through translocon
into lumen (Type 3).
- The SA becomes the transmembrane domain.
Type 2
- N-terminal in Cytosol
- SA is transmembrane
- C-terminal in lumen
Type 3
- C-terminal in Cytosol
- SA in transmembrane
- N-terminal in lumen
find more resources at oneclass.com
find more resources at oneclass.com
Type 4 Transmembrane Proteins
- Alternating Signal Anchor sequences and Stop Transfer sequences lumen, cytosol, lumen, cytosol, lumen...
- Both signals become transmembrane domains
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
As protein is translated in cytosol, ribosome hits topogenic sequences that tells it what to do w/the protein. N-terminal signal sequence tells ribosome to go to er (secreted protein) Stop transfer anchor sequence (sta) stops transfer and anchors protein into membrane. Signal anchor sequence (sa) tells ribosome to go to er (internal, uncleaved sequence). C-terminal domain in membrane and n-terminal domain in cytoplasm (no extracellular domain). Ribosome encounters hydrophobic c-terminal tail and recruits get3. Get3 gets the protein to the er and membrane-embedded get1 and. Get2 shove the protein into the plasma membrane using atp hydrolysis. 2 topogenic sequences n-terminal and sta. Ribosome encounters n-terminal signal sequence that is recognized by srp. Srp takes protein to er and puts it through translocon. Ribosome translates in lumen but then encounters sta. Sta stop transferring into lumen, start transferring into cytosol. N-terminus is in lumen, sta is transmembrane, c-terminus is in cytosol.
