Concluding Remarks: Mechanism of Functional Expression Common in the Molecular Machines
Let us take protein folding as an example. The initial and final states of the folding process are visually different: Protein is in unfolded and folded states, respectively. Therefore, it can readily be understood that protein folding spontaneously occur
- PDF / 200,907 Bytes
- 8 Pages / 439.37 x 666.142 pts Page_size
- 99 Downloads / 159 Views
Concluding Remarks: Mechanism of Functional Expression Common in the Molecular Machines
Abstract Let us take protein folding as an example. The initial and final states of the folding process are visually different: Protein is in unfolded and folded states, respectively. Therefore, it can readily be understood that protein folding spontaneously occurs as an irreversible process accompanying a decrease in the system free energy. On the other hand, the conformations of F1-ATPase before and after a 120° rotation of the central subunit, for example, are the same. Nevertheless, the directed rotation occurs. Hence, in the prevailing view, this rotation process is differently treated: It is made possible by converting the free energy of ATP hydrolysis to a work, and F1-ATPase is referred to as “molecular rotatory machine.” The work is necessary for the central subunit (i.e., γ subunit) to rotate against the viscous resistance force by water. Similarly, the unidirectional movement of S1 is realized by converting the free energy of ATP hydrolysis to a work that is necessary for S1 to move against the viscous resistance force by water. We disagree with this view (also see Sect. 3.2.5) In this chapter, we argue that protein folding and the directed rotation, for example, can be treated within the same theoretical framework. Keywords ATP-driven protein · Motor protein · Molecular machine · Irreversible process
4.1 Characteristics Common in ATP-Driven Proteins and Protein Complexes Water forms a potential field between the myosin-F-actin, protein-chaperonin, and substrate-ABC transporter pairs, as argued in Sects. 3.2, 3.3, and 3.4, respectively. The entropic component of the field is substantial, but the energetic component is also important for a chaperonin. The field is strongly dependent on the structure and properties of the pairs. When the ATP concentration is sufficiently high and the ADP and Pi concentrations are sufficiently low, the dissociation of ADP or Pi from as well as the binding of ATP to a receptor decreases the system free energy (SFE): © The Author(s) 2016 M. Kinoshita, Mechanism of Functional Expression of the Molecular Machines, SpringerBriefs in Molecular Science, DOI 10.1007/978-981-10-1486-4_4
63
64
4 Concluding Remarks: Mechanism of Functional Expression Common …
They unavoidably occur. The hydrolysis of ATP within the receptor accompanies a small decrease in the SFE. The occurrence of any of the ATP binding, hydrolysis, and dissociation of ADP or Pi perturbs the structure and properties of the pairs. The perturbation causes an alteration of the potential field. Through this mechanism, a variety of functions such as the unidirectional movement of myosin and insertion and release of a protein or a substrate are exhibited. In each cycle, the original configuration of myosin, chaperonin, or ABC transporter is recovered and the cycle is repeatable. One ATP molecule is hydrolyzed in each cycle for actomyosin and the SFE decreases by the free energy of ATP hydrolysis in aqueous solution, FH (se
Data Loading...
