Functional mechanisms of ABC transporters as revealed by molecular simulations

Abstract

Active transport in cells is accomplished by a class of integral membrane proteins known as ATP-binding cassette (ABC) transporters. The energy source powering these molecular machines is the free energy generated by the binding of ATP molecules to nucleotide-binding domains (NBDs), as well as the free energy generated by ATP hydrolysis. The opening and closing motions of the NBDs are driven by these energies, which are propagated through transmembrane domains (TMDs) via mechanical transmission segments (coupling helices). As a result, the opening and closing motions of the TMDs are generated, which allow the uptake and release of substrates. In these processes, the chemical energy of ATP is converted into mechanical motion, a typical example of chemo-mechanical coupling. In this review, we describe the current understanding of this coupling mechanism, with a focus on the cooperative role of ATP and water.