3.6 Inverse Rotation Under Solution Condition …
53
3.6.2 Details of Rotation Mechanism
We infer that the rotation mechanism is the following (see Fig. 3.21).
(1) ADP binds to β E , ATP dissociates from β TP , and “ATP• • •H 2 O→ATP(ATP•
• •H 2 O)” (change of ATP• • •H 2 O toward ATP) occurs in β DP in state change
(a)→(b). These three events lead to enhanced, lowered, and lowered packing
efficiencies of β E , β TP , and β DP , respectively (see Fig. 3.14), and the packings of subcomplexes I−γ, II−γ, and III−γ become closer, looser, and looser,
respectively.
(2) In state change (b)→(c), ATP synthesis (ADP + Pi→ATP• • •H 2 O) occurs
in β’ E , Pi binds to β’ TP , and “ATP(ATP• • •H 2 O)→ATP” (further change of
ATP• • •H 2 O toward ATP) occurs in β’ DP . These three events lead to enhanced,
lowered, and lowered packing efficiencies of β’ E , β’ TP , and β’ DP , respectively
(see Fig. 3.14), and the packings of subcomplexes I−γ, II−γ, and III−γ become
closer, looser, and looser, respectively.
Dissociation of
ATP from β TP
ADP binding
to β E
Pi binding
to β’ TP
(b)
(a)
(c)
ATP synthesis
in β’ E
Loose
Close
Moderate
Closer
Looser
Looser
Closer
Looser
Looser
Close
Moderate
Loose
80 o
rotation
40 o
rotation
ADP+Pi→ATP H 2 O
ATP(ATP H 2 O) ATP
ATP H 2 O
ATP(ATP H 2 O)
Fig. 3.21 Our physical picture of rotation mechanism of γ subunit in α 3 β 3 γ complex during one
ATP synthesis cycle in scenario (B. “ATP• • •H 2 O” represents ATP just after the synthesis reaction.
ATP(ATP• • •H 2 O) represents an intermediate between ATP and ATP• • •H 2 O. The packing of β E
(and subcomplex I−γ) is loose in state (a) but it becomes closer in stage change (a)→(b). The
packing of β’ E (and subcomplex I−γ) becomes further closer in (b)→(c). The packing of β DP (and
subcomplex I−γ) is now close in (c). The packing of β TP (and subcomplex II−γ) is moderate in
(a) but it becomes looser in (a)→(b). The packing of β’ TP (and subcomplex II−γ) becomes further
looser in (b)→(c). The packing of β E (and subcomplex II−γ) is now loose in (c). The packing of
β DP (and subcomplex III−γ) is close in (a) but it becomes looser in (a)→(b). The packing of β’ DP
(and subcomplex III−γ) becomes further looser in (b)→(c). The packing of β TP (and subcomplex
III−γ) is now moderate in (c)
53
3.6.2 Details of Rotation Mechanism
We infer that the rotation mechanism is the following (see Fig. 3.21).
(1) ADP binds to β E , ATP dissociates from β TP , and “ATP• • •H 2 O→ATP(ATP•
• •H 2 O)” (change of ATP• • •H 2 O toward ATP) occurs in β DP in state change
(a)→(b). These three events lead to enhanced, lowered, and lowered packing
efficiencies of β E , β TP , and β DP , respectively (see Fig. 3.14), and the packings of subcomplexes I−γ, II−γ, and III−γ become closer, looser, and looser,
respectively.
(2) In state change (b)→(c), ATP synthesis (ADP + Pi→ATP• • •H 2 O) occurs
in β’ E , Pi binds to β’ TP , and “ATP(ATP• • •H 2 O)→ATP” (further change of
ATP• • •H 2 O toward ATP) occurs in β’ DP . These three events lead to enhanced,
lowered, and lowered packing efficiencies of β’ E , β’ TP , and β’ DP , respectively
(see Fig. 3.14), and the packings of subcomplexes I−γ, II−γ, and III−γ become
closer, looser, and looser, respectively.
Dissociation of
ATP from β TP
ADP binding
to β E
Pi binding
to β’ TP
(b)
(a)
(c)
ATP synthesis
in β’ E
Loose
Close
Moderate
Closer
Looser
Looser
Closer
Looser
Looser
Close
Moderate
Loose
80 o
rotation
40 o
rotation
ADP+Pi→ATP H 2 O
ATP(ATP H 2 O) ATP
ATP H 2 O
ATP(ATP H 2 O)
Fig. 3.21 Our physical picture of rotation mechanism of γ subunit in α 3 β 3 γ complex during one
ATP synthesis cycle in scenario (B. “ATP• • •H 2 O” represents ATP just after the synthesis reaction.
ATP(ATP• • •H 2 O) represents an intermediate between ATP and ATP• • •H 2 O. The packing of β E
(and subcomplex I−γ) is loose in state (a) but it becomes closer in stage change (a)→(b). The
packing of β’ E (and subcomplex I−γ) becomes further closer in (b)→(c). The packing of β DP (and
subcomplex I−γ) is now close in (c). The packing of β TP (and subcomplex II−γ) is moderate in
(a) but it becomes looser in (a)→(b). The packing of β’ TP (and subcomplex II−γ) becomes further
looser in (b)→(c). The packing of β E (and subcomplex II−γ) is now loose in (c). The packing of
β DP (and subcomplex III−γ) is close in (a) but it becomes looser in (a)→(b). The packing of β’ DP
(and subcomplex III−γ) becomes further looser in (b)→(c). The packing of β TP (and subcomplex
III−γ) is now moderate in (c)