Lecture 10: Assembly of Proteins into Membranes 2 Flashcards
How is their pseudo symmetry in Sec61 in eukaryotes?
5TM domains in one half (TM1-5) and 5 in the other half (TM6-10).
Where is the lateral gate opening?
Between TMs 2 and 7
What is the pore ring? Why is it needed?
formed at a constriction point of isoleucine residues that form a hydrophobic gasket around the proteins moving into the channel. Stops ions leaking back through destroying ion gradients when the plug is displaced.
What does the plug do?
Blocks the channel
How was it previously thought the seal was maintained?
By the ribosome forming a tight seal
What is the mode of insertion of translocation machinery in E.coli? How does it differ to eukaryotic?
Post translational rather than cotranslational
What does insertion in E.coli involve?
SecA which has no eukaryotic homologue
What do chaperones do in E.coli?
Keep the protein in an unfolded conformation
What does SecA do and how is this different to eukaryotes?
Hydrolysis ATP to drive the protein through the channel whereas in eukaryotes this is driven by translation
How was biogenesis of integral membrane proteins initially studied? What was found?
Using SecA inhibitor, sodium azide. Only large domains of IMPs require Sec machinery and others didn’t require it as they assembled into the membrane well
What did sequencing the genome of E.coli reveal? What are they involved with?
Ffh and FtsY. Assembly of integral membrane proteins
What was it thought Ffh was involved with? What is the issue with this?
halting translation. Don’t need to halt translation in E.coli.
List the differences between eukaryotes and E.coli
Eukaryotes are mostly co-translational, E.coli is post translational
Eukaryotes have no SecA homologue
Eukaryotes have TRAM, E.coli has YidC
What is YidC analogous to?
TRAM
What could YidC be?
An alternate translocon to Sec61/SecY in E.coli
Where is there a YidC homologue? What is it called?
Mitochondria. Oxa1p
What does YidC depletion affect?
Assembly of integral membrane proteins
What is the proposed mechanism of action of YidC?
provides a hydrophilic environment within the membrane for transporting hydrophilic substrates. It exposes hydrophobic parts of proteins to the hydrophobic bilayer. It thins the membrane.
What is retrotranslocation?
Movement of proteins back from the ER to the cytoplasm labelling then with Ub so they can be degraded by the proteosome. Hrd1 and Hrd3 perform this ERAD process.
