GroEl and GroES appearance and function

Question 1

GroEL basic structure

Answer 1

• 2 GroEL rings ( no passage between them)
• cis and trans
• 1 ring active at a time, but need both of them’
• cis ring is the active form

Question 2

Domains in the 7 GroEL 60 kD identical subunits per ring

Answer 2

• 3 domains:
  Equatorial
  apical
  intermediate

Question 3

equatorial domain in GroEL subunit

Answer 3

holds subunits together and binds ATP in specific pockets

Question 4

Apical domain in groel subunit

Answer 4

has hydrophobic patches, for interacting hydrophobically with misfolded proteins and bind hydrophobic regions on the groES cap

Question 5

Intermediate domain in groel subunit

Answer 5

connects the two domains
interior becomes a hydrophilic chamber, isolates the misfolded protein from nonpolar regions and forces it to fold appropriately

Question 6

ATP binding

Answer 6

• occurs in currently active ring (cis)
• positive cooperativity vis salt bridge
• atp binding pockets open into the center cavity until groES binds (via saltbridge)
• binding in cis prevents atp binding to trans via small changes in conformation

Question 7

positive cooperation

Answer 7

when one atp binds, easier for the next to bind

Question 8

GroEL cap

Answer 8

• 7 identical 10 kD subunits
• hydrophilic inner surface

Question 9

Where in the GroEL chaperone protein are misfolded proteins held

Answer 9

• H and I helices of apical domain

Question 10

how are misfolded proteins held with cap

Answer 10

protein - like a cork in a bottle
cap - not a tight cap

Question 11

H and I helices

Answer 11

• H and I helices repositiion themselves between binding misfolded protein and then drop the protein inside.

Question 12

Why do H and I helices resposition themselves between misfolded proteins and drop them inside?

Answer 12

• you can only hold onto something hydrphobically for so long….
• youre going to be stretching, and then drop the protein
• when you stretch, you pull the protein out of a local energy minima (one of the lost pathways)
• now protein can refold

Question 13

apical domain moves…

Answer 13

upward and outward

Question 14

When does atp interact with groel and groes

Answer 14

atp is enclosed in the groel complex once groes is bound
- atp stabilizes the complex until atp is hydrolyzed
- A chemical reaction then occurs that releases groes and the protein

Question 15

What causes the cis ring to open up

Answer 15

when atp binds to the equatorial cis ring pockets, causes a stabilizing reaction to occur that causes an opening up, which allows the cap to reside

Question 16

Hydrolysis effect on groes/groel complex

Answer 16

atp hydrolysis destabilizes the complex, causing the cis ring to not be opened up anymore, which causes the groes to leave and allows the protein to diffuse out

Question 17

What is the purpose of atp and is it wasted

Answer 17

atp is responsible for release of the protein and groes cap, helps to relax conformational changes to allow the cap to not be bound anymore