32
3 Mechanism of Unidirectional Rotation of γ Subunit in F 1 -ATPase
Fig. 3.3 Ribbon representation of α 3 β 3 γ-complex structure shown in Fig. 3.2a. a Top view. b Side
view. The α subunits, β subunits, and γ subunit are colored green, yellow, and gray, respectively.
AMP-PNP is represented by the red fused spheres
Fig. 3.4 Structure of α 3 β 3 γ
complex to which
nucleotides are not bound
[5]. The α 3 β 3 γ complex is
immersed in aqueous
solution containing no
nucleotides
α
β
β
α
α
β
Open
Structure
Closed
Structure
Closed
Structure
γ
Without nucleotides bound
that the interaction between the γ subunit and the α 3 β 3 complex is as important as
the nucleotide occupancy in determining the structural state of the three β subunits.
Taken together, the α 3 β 3 or α 3 β 3 γ complex stabilized (i.e., irrespective of the
presence of the γ subunit) is characterized by two β subunits possessing closed
structure with nucleotides bound and one β subunit possessing open structure without
nucleotides bound. Presumably, if all the three β subunits took closed structure, it
would become impossible to form sufficiently close overall packing of the atoms in
the six α−β interfaces, which was less favorable in terms of the water entropy. It is
important to note that the incorporation of the γ subunit in the α 3 β 3 complex also
leads to the state characterized by two β subunits possessing closed structure and
one β subunit possessing open structure, definitely due to the structural asymmetry
inherent in the γ subunit. The specific packing structure of the α 3 β 3 complex is
stabilized either by the nonuniform nucleotide binding or the incorporation of the γ
subunit, but it is further stabilized when both of them are conferred upon the complex.
3 Mechanism of Unidirectional Rotation of γ Subunit in F 1 -ATPase
Fig. 3.3 Ribbon representation of α 3 β 3 γ-complex structure shown in Fig. 3.2a. a Top view. b Side
view. The α subunits, β subunits, and γ subunit are colored green, yellow, and gray, respectively.
AMP-PNP is represented by the red fused spheres
Fig. 3.4 Structure of α 3 β 3 γ
complex to which
nucleotides are not bound
[5]. The α 3 β 3 γ complex is
immersed in aqueous
solution containing no
nucleotides
α
β
β
α
α
β
Open
Structure
Closed
Structure
Closed
Structure
γ
Without nucleotides bound
that the interaction between the γ subunit and the α 3 β 3 complex is as important as
the nucleotide occupancy in determining the structural state of the three β subunits.
Taken together, the α 3 β 3 or α 3 β 3 γ complex stabilized (i.e., irrespective of the
presence of the γ subunit) is characterized by two β subunits possessing closed
structure with nucleotides bound and one β subunit possessing open structure without
nucleotides bound. Presumably, if all the three β subunits took closed structure, it
would become impossible to form sufficiently close overall packing of the atoms in
the six α−β interfaces, which was less favorable in terms of the water entropy. It is
important to note that the incorporation of the γ subunit in the α 3 β 3 complex also
leads to the state characterized by two β subunits possessing closed structure and
one β subunit possessing open structure, definitely due to the structural asymmetry
inherent in the γ subunit. The specific packing structure of the α 3 β 3 complex is
stabilized either by the nonuniform nucleotide binding or the incorporation of the γ
subunit, but it is further stabilized when both of them are conferred upon the complex.