Scribe.Lecture 27.docx

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University of Toronto St. George
Cell and Systems Biology
William Navarre

Lecture 27 7 1. protein of interest that is going through the IM has a N-terminal signal seq 2. the seq tells the bacteria that it needs to be transported out of the cytoplasm 3. the signal seq is bound by the chaperone SecB 1. maintains the protein 2. binds to the protein to prevent premature folding 4. SecB then interacts w SecAATPase 5. and this is then able to bring the protein to the sec secretion sys 6. SecA upon binding to ATP results in the release of SecB chaperone so it could go and bind other substrates 7. release of SecB initiates translocation process 1. protein begins to be put through the channel (but not all the way through yet) 8. SecA hydrolyzes ATP and the NRG drives the protein through the channel 9. protein’s signal seq domain still remains inside the sec secretion sys 1. in order to fully release it, requires a signal peptidase that cleaves the seq and releases the protein 10. the protein will now be outside the cell (gm+) or in the periplasm (gm-) 8 11. the signal seq is at the N terminus, it has 3 main domains 1. N domain: short, mostly positively charged residues 2. H domain: hydrophobic 3. C domain: polar, contains the cleavage site 9 12. proteins that are put into the membrane contain hydrophobic regions 13. to accommodate hydrophobic regions in the cytoplasm, as the protein is being translated by the ribosome, they are going to expose a SRP signal seq which recruits SRP which is going to interact w the ribosome and dock it onto the membrane to the GTP-bound FtsY 14. GTP hydrolyses transfers the ribosome plus the protein it is currently translating, to the sec secretion sys 15. the hydrophobic region is going to slip into the membrane 16. co-translational translocation 10 17. proteins that are anchored to the membrane contain an additional signal motif (LPXTG) 18. as the protein goes through the sec secretion sys, a hydrophobic region is going to stick into the membrane 19. an endopeptidase is going to cut this 20. the LPXTG seq is going to be recognized by a sortase 21. through a series of rxns, the sortase transfers the protein onto a lipid anchor 22. the end product is a protein tethered to the membrane with a lipid anchor 23. both the N and C terminus are removed in tethered proteins 1. the N terminus is removed after interaction w the Sec secretion sys 2. the C terminus is removed after interaction w the sortase 11 24. gm- bacteria have an additional OM 25. both the IM & OM are impermeable 26. the periplasm has a unique envmt (no ATP) 1. can’t use NRG to drive transport 27. make more secretion systems to overcome this 28. a lot of secretion systems build upon sec secretion systems 1. sec-dependent secretion systems (building upon what sec secretions systems are doing, taking a protein from the periplasm and move it across the OM) 12 29. autotransporters transport themselves across the OM 30. through the sec secretion system, they are able to get into the periplasm (through their sec signal seq, which is cleaved off) 31. the protein additionally has a c-terminal beta domain 1. spontan
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