Dissecting the role of the γ-subunit in the rotary-chemical coupling and torque generation of F1-ATPase.
Unraveling the molecular nature of the conversion of chemical energy (ATP hydrolysis in the α/β-subunits) to mechanical energy and torque (rotation of the γ-subunit) in F1-ATPase is very challenging. A major part of the challenge involves understanding the rotary-chemical coupling by a nonphenomenological structure-energy description, while accounting for the observed torque generated on the γ-subunit and its change due to mutation of this unit. Here we extend our previous study that used a coarse-grained model of the F1-ATPase to generate a structure-based free energy landscape of the rotary-chemical process. Our quantitative analysis of the landscape reproduced the observed torque for the wild-type enzyme. In doing so, we found that there are several possibilities of torque generation from landscapes with various shapes and demonstrated that a downhill slope along the chemical coordinate could still result in negligible torque, due to ineffective coupling of the chemistry to the γ-subunit rotation. We then explored the relationship between the functionality and the underlying sequence through systematic examination of the effect of various parts of the γ-subunit on free energy surfaces of F1-ATPase. Furthermore, by constructing several types of γ-deletion systems and calculating the corresponding torque generation, we gained previously unknown insights into the molecular nature of the F1-ATPase rotary motor. Significantly, our results are in excellent agreement with recent experimental findings and indicate that the rotary-chemical coupling is primarily established through electrostatic effects, although specific contacts through γ-ionizable residue side chains are not essential for establishing the basic features of the coupling.
Department of Chemistry, University of Southern California, Los Angeles, CA 90089-1062.
Shayantani
S
Mukherjee
Department of Chemistry, University of Southern California, Los Angeles, CA 90089-1062 warshel@usc.edu.
Arieh
A
Warshel
D008956:Models, Chemical; D008958:Models, Molecular; D009038:Motion; D009154:Mutation; D006180:Proton-Translocating ATPases / Q000737:chemistry* / Q000235:genetics; D055672:Static Electricity
C444660:gamma subunit, F(1) ATPase; D006180:Proton-Translocating ATPases
F0F1-ATPsynthase; bioenergetics; free energy surface; molecular motors; rotary torque