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Importance of water entropy in rotation mechanism of F 1 -ATPase

View Article: PubMed Central - PubMed

ABSTRACT

We briefly review our theoretical study on the rotation scheme of F1-ATPase. In the scheme, the key factor is the water entropy which has been shown to drive a variety of self-assembly processes in biological systems. We decompose the crystal structure of F1-ATPase into three sub-complexes each of which is composed of the γ subunit, one of the β subunits, and two α subunits adjacent to them. The βE, βTP, and βDP subunits are involved in the sub-complexes I, II, and III, respectively. We calculate the hydration entropy of each sub-complex using a hybrid of the integral equation theory for molecular liquids and the morphometric approach. It is found that the absolute value of the hydration entropy follows the order, sub-complex I > sub-complex II > sub-complex III. Moreover, the differences are quite large, which manifests highly asymmetrical packing of F1-ATPase. In our picture, this asymmetrical packing plays crucially important roles in the rotation of the γ subunit. We discuss how the rotation is induced by the water-entropy effect coupled with such chemical processes as ATP binding, ATP hydrolysis, and release of the products.

No MeSH data available.


Ribbon representation of the α3β3γ complex viewed from the Fo side11. The γ subunit, represented by yellow ribbon, rotates in a counterclockwise direction1. This figure is drawn using the DS visualizer 2.5.
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f1-7_113: Ribbon representation of the α3β3γ complex viewed from the Fo side11. The γ subunit, represented by yellow ribbon, rotates in a counterclockwise direction1. This figure is drawn using the DS visualizer 2.5.

Mentions: FoF1-ATP synthase is a molecular motor found in biological membranes. It is composed of a water-soluble part, F1, and a membrane-embedded part, Fo. Coupled with proton transport across membranes, F1-part of the synthase produces adenosine triphosphate (ATP) from adenosine diphosphate (ADP) and inorganic phosphate (Pi). F1-ATPase, F1-part of the synthase, is a rotary molecular motor induced by such chemical processes as the ATP binding, ATP hydrolysis, and release of products (ADP and Pi). In the present review, we focus on the α3β3γ complex in F1-ATPase, which has widely been studied in single-molecule experiments1–10. According to the atomic-level crystal structures11–14 of the α3β3γ complex, the α3β3 subunits are arranged hexagonally around the γ subunit as shown in Figure 1. During the cycle of the chemical processes mentioned above, the γ subunit rotates in a counterclockwise direction when it is viewed from the Fo side1. The γ subunit performs a 120° step rotation during hydrolysis of a single ATP molecule2. This step is further resolved into 80° and 40° substeps. The 80° substep is induced by ATP binding3 and/or release of ADP5. Subsequent ATP hydrolysis occurs in 1ms without the rotation4, which is followed by the 40° rotation accompanying release of Pi6. Release of ADP occurs during the 80° rotation5. The 80° and 40° dwells are referred to as catalytic and ATP-waiting dwells, respectively4.


Importance of water entropy in rotation mechanism of F 1 -ATPase
Ribbon representation of the α3β3γ complex viewed from the Fo side11. The γ subunit, represented by yellow ribbon, rotates in a counterclockwise direction1. This figure is drawn using the DS visualizer 2.5.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC5036781&req=5

f1-7_113: Ribbon representation of the α3β3γ complex viewed from the Fo side11. The γ subunit, represented by yellow ribbon, rotates in a counterclockwise direction1. This figure is drawn using the DS visualizer 2.5.
Mentions: FoF1-ATP synthase is a molecular motor found in biological membranes. It is composed of a water-soluble part, F1, and a membrane-embedded part, Fo. Coupled with proton transport across membranes, F1-part of the synthase produces adenosine triphosphate (ATP) from adenosine diphosphate (ADP) and inorganic phosphate (Pi). F1-ATPase, F1-part of the synthase, is a rotary molecular motor induced by such chemical processes as the ATP binding, ATP hydrolysis, and release of products (ADP and Pi). In the present review, we focus on the α3β3γ complex in F1-ATPase, which has widely been studied in single-molecule experiments1–10. According to the atomic-level crystal structures11–14 of the α3β3γ complex, the α3β3 subunits are arranged hexagonally around the γ subunit as shown in Figure 1. During the cycle of the chemical processes mentioned above, the γ subunit rotates in a counterclockwise direction when it is viewed from the Fo side1. The γ subunit performs a 120° step rotation during hydrolysis of a single ATP molecule2. This step is further resolved into 80° and 40° substeps. The 80° substep is induced by ATP binding3 and/or release of ADP5. Subsequent ATP hydrolysis occurs in 1ms without the rotation4, which is followed by the 40° rotation accompanying release of Pi6. Release of ADP occurs during the 80° rotation5. The 80° and 40° dwells are referred to as catalytic and ATP-waiting dwells, respectively4.

View Article: PubMed Central - PubMed

ABSTRACT

We briefly review our theoretical study on the rotation scheme of F1-ATPase. In the scheme, the key factor is the water entropy which has been shown to drive a variety of self-assembly processes in biological systems. We decompose the crystal structure of F1-ATPase into three sub-complexes each of which is composed of the γ subunit, one of the β subunits, and two α subunits adjacent to them. The βE, βTP, and βDP subunits are involved in the sub-complexes I, II, and III, respectively. We calculate the hydration entropy of each sub-complex using a hybrid of the integral equation theory for molecular liquids and the morphometric approach. It is found that the absolute value of the hydration entropy follows the order, sub-complex I > sub-complex II > sub-complex III. Moreover, the differences are quite large, which manifests highly asymmetrical packing of F1-ATPase. In our picture, this asymmetrical packing plays crucially important roles in the rotation of the γ subunit. We discuss how the rotation is induced by the water-entropy effect coupled with such chemical processes as ATP binding, ATP hydrolysis, and release of the products.

No MeSH data available.