Exam 2 Lecture 14 Flashcards
(26 cards)
What do chaperones do?
Help fold proteins in the cytoplasm, unfold and refold misfolds, target misfolds for degradation, prevent full folding before protein reaches it’s final target
Examples Hsp 60, 70 or 40
Do chaperons use ATP?
Yes Hsp-60 is an example
In bacteria how do proteins make it to their final targets?
- Default stays in cytoplasm
- Secreted using target signal and Sec apparatus before tert and quat folding happens
- Already folded proteins with target signal exported with cofactors by TAT apparatus
- There are dedicated secretion pathways specific to some bacteria
How does co-translational secretion into the membrane happen?
- Ribosome starts to translate protein which has a signal sequence (20-25 hydrophobic residues) in it
- SRP protein recognizes signal sequence and binds to ribosome pausing translation
- Brings it to the FtsY receptor in the membrane
4 Peptide is inserted to membrane and peptide is translated via SecYEG channel
Targeting signal remains as part of the final protein in the membrane
Sometimes (rare) it is inserted directly not using FtsY and SecYEG
How are proteins secreted through the membrane?
- Translation is completed and they have an N term signal sequence recognized by Sec B and delivered to SecA
2 SecA takes to SecYEG channel and threads it through using ATP and proton motive force
- Once protein is through LepB cleaves signal and periplasmic proteins fold
In gram negative where is the SecYEG located?
Only on the inner membrane
What keeps a protein target for secretion unfolded before it is secreted?
Chaperones like SecB or Hsp70
Bacteria unfolded protein secretion- co or post transcription? What proteins and how is it powered?
Both, uses SecYEG and SecA or SRP
Powered by ATP and PMF or just PMF
Archaea unfolded protein secretion- co or post transcription? What proteins and how is it powered?
Cotranslationaly uses SecYEbeta
probably PMF dependant
Eukarya unfolded protein secretion- co or post transcription? What proteins and how is it powered?
Both, using SEC61 with SRPor via ER and golgi
How do bacteria move folded proteins across the membrane?
TatABC
What is the TAT targeting signal?
N- term Twin- Arg- Tag
What does the TAT signal do?
- Signals to TatB and C (which are localized in membrane to bind to it and pre-curser associates
- This recruits TatAs that assemble a TatABC complex and surround folded protein exporting it using proton motive force
True False Tat targeting signal is cleaved after export?
True
Differences between TAT and SEc targeting sequences?
Tat has basic (+) AAs in both N (RR) and C regions (AxA)
Both have a hydrophobic h region
Sec has 20-25 hydrophobic residues
Both get cleaved
Is SecYEG and TAT conserved?
Yes all bacteria and archaea contain SecYEG and many have TAT too
How many known specialized bacterial protein export systems are there?
Nine
Do specialized bacterial protein export systems require energy?
Yes all do but some use Sec to get across the inner membrane
True/False- Specialized bacterial protein export systems are essential for growth
False they aren’t but are often associated with traits like parthenogenesis
Does every specialized bacterial protein export system Type export the same protein all the time?
No, the specific types genes are mostly conserved but the secreted proteins can be very different
Example P aeruginosa has 25-30 different systems for different proteins of T1, T2 T3, T5 and T6 types.
Their Type 2 is SecA dependant
What is one Gram negative specific secretion apparatus?
Type III, it has specific TS3 target signal and uses ATP
Often used to deliver toxins direct from a pathenogenic bacteria cytoplasm to a eukaryotic host also call an injectosome
What have Type III systems been reengineered to?
A Flagella motor, it secretes the flagella (as many as 20,000 subunits) then spins it using ATP!
What are the most abundant gene groups?
Translation, metabolism and transport
2 ways evolution can happen?
Stepwise or big steps where lots of material is gained or lost at once
