ATP synthase

Question 1

What is the structure of the F1 portion of ATP synthase?

Answer 1

F1 portion is formed of 5 different subunits: alpha, beta, gamma, epsilon, and delta

• the alpha and beta subunits form a hexameric ring structure of alternating subunits around the central gamma subunit.
• the gamma subunit is connected to the F0 portion and rotates against the a3b3 subunit.
• the delta subunit is connected to the stator to ensure the a3b3 hexamer remains stationary

Question 2

What is the structure of the F0 portion of ATP synthase?

Answer 2

F0 portion is formed of 3 different subunits: a, b, and c (

• the b subunits form a dimer that act as a stator to interact with the a3b3 hexamer and keep it stationary
• the a subunit contains half channels that access either the P or N side.
• the c subunits have a conserved Glu/Asp 61 residue and the subunits form a ring against the a subunit so that the 61 amino acid has access to both half channels but not at the same time.

Question 3

Explain the rotational catalysis mechanism of ATP synthase?

Answer 3

1) 61 amino acid in the P half channel of the a subunit and since there is a high concentration of H+, the pH is greater than the pKa of the amino acid, so it becomes protonated and now hydrophobic so moves into the membrane, causing rotation of the c subunits and one 61 amino acid enters the N half channel of the a subunit.
2) Since there is a lower concentration of H+ on the N side, the pH is less than the pKa of the amino acid, so it is deprotonated and the H+ diffuses into the N side.
3) the rotation of the c subunits causes the rotation of the gamma subunit relative to the stationary a3b3 hexamer, which forces the tight state beta subunit (bound to ADP and Pi) into the empty state and the release of the products.

Question 4

Which portion of ATP synthase is the catalytic portion?

Answer 4

F1 (specifically the beta subunits)

Question 5

What are the two experiments that showed the rotation of the gamma subunit relative to the beta subunits?

Answer 5

1) His tags added to the beta subunits to attach the F1 portion to a Ni-coated plate by the beta subunits (which keeps then stationary). The gamma subunit was fluorescently tagged and ATP substrate supplied - showed ATP hydrolysis
2) His tags added to the beta subunits to attach the F1 portion to a Ni-coated plate by the beta subunits (which keeps then stationary). The gamma subunit was attached to magnetic beads and a magnet was used to rotate attract the beads and rotate the gamma subunit and the production of ATP was detected by the luciferin-luciferase mechanism (hydrolyse ATP to emit a photon) - showed ATP synthesis