Exam 2 Lecture 14

Question 1

What do chaperones do?

Answer 1

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

Question 2

Do chaperons use ATP?

Answer 2

Yes Hsp-60 is an example

Question 3

In bacteria how do proteins make it to their final targets?

Answer 3

1. Default stays in cytoplasm
2. Secreted using target signal and Sec apparatus before tert and quat folding happens
3. Already folded proteins with target signal exported with cofactors by TAT apparatus
4. There are dedicated secretion pathways specific to some bacteria

Question 4

How does co-translational secretion into the membrane happen?

Answer 4

1. Ribosome starts to translate protein which has a signal sequence (20-25 hydrophobic residues) in it
2. SRP protein recognizes signal sequence and binds to ribosome pausing translation
3. 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

Question 5

How are proteins secreted through the membrane?

Answer 5

1. 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

3. Once protein is through LepB cleaves signal and periplasmic proteins fold

Question 6

In gram negative where is the SecYEG located?

Answer 6

Only on the inner membrane

Question 7

What keeps a protein target for secretion unfolded before it is secreted?

Answer 7

Chaperones like SecB or Hsp70

Question 8

Bacteria unfolded protein secretion- co or post transcription? What proteins and how is it powered?

Answer 8

Both, uses SecYEG and SecA or SRP

Powered by ATP and PMF or just PMF

Question 9

Archaea unfolded protein secretion- co or post transcription? What proteins and how is it powered?

Answer 9

Cotranslationaly uses SecYEbeta

probably PMF dependant

Question 10

Eukarya unfolded protein secretion- co or post transcription? What proteins and how is it powered?

Answer 10

Both, using SEC61 with SRPor via ER and golgi

Question 11

How do bacteria move folded proteins across the membrane?

Answer 11

TatABC

Question 12

What is the TAT targeting signal?

Answer 12

N- term Twin- Arg- Tag

Question 13

What does the TAT signal do?

Answer 13

1. Signals to TatB and C (which are localized in membrane to bind to it and pre-curser associates
2. This recruits TatAs that assemble a TatABC complex and surround folded protein exporting it using proton motive force

Question 14

True False Tat targeting signal is cleaved after export?

Answer 14

True

Question 15

Differences between TAT and SEc targeting sequences?

Answer 15

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

Question 16

Is SecYEG and TAT conserved?

Answer 16

Yes all bacteria and archaea contain SecYEG and many have TAT too

Question 17

How many known specialized bacterial protein export systems are there?

Answer 17

Nine

Question 18

Do specialized bacterial protein export systems require energy?

Answer 18

Yes all do but some use Sec to get across the inner membrane

Question 19

True/False- Specialized bacterial protein export systems are essential for growth

Answer 19

False they aren’t but are often associated with traits like parthenogenesis

Question 20

Does every specialized bacterial protein export system Type export the same protein all the time?

Answer 20

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

Question 21

What is one Gram negative specific secretion apparatus?

Answer 21

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

Question 22

What have Type III systems been reengineered to?

Answer 22

A Flagella motor, it secretes the flagella (as many as 20,000 subunits) then spins it using ATP!

Question 23

What are the most abundant gene groups?

Answer 23

Translation, metabolism and transport

Question 24

2 ways evolution can happen?

Answer 24

Stepwise or big steps where lots of material is gained or lost at once

Question 25

Did Ecoli and S enterica (salmonnella) share a common ancestor

Answer 25

Yes