The stalks of the motor A1A0 ATP synthase come into the focus : structural insight into subunits E, F and H
Date of Issue2010
School of Biological Sciences
A1AO adenosine triphosphate (ATP) synthases from archaea represent the second class of ATP synthases due to their unusual structural and mechanistic features, which may be due to archaea’s unique phylogenetic position in the tree of life. The enzyme uses both H+ and Na+ ion gradients across the membrane to synthesize ATP. A1AO ATP synthases comprises subunits in the stoichiometry of A3:B3:C:D:Ex:F:H2:a:cx. The water soluble A1 domain (A3:B3) has a pseudohexagonal arrangement of major subunits A and B and it is responsible for ATP synthesis or hydrolysis. The energy provided for or released during the process of ATP hydrolysis or synthesis is transmitted via the stalk parts to the membrane-bound AO domain to facilitate ion conduction. The stalk parts have an important role for the regulation of this class of enzymes and are separated into a central part (C:D:F) and peripheral parts (Ex:H2:aN). In order to get a detailed picture, structural characterization has been done for the central stalk subunit F and the peripheral stalk subunits H and E. The solution structure of the central stalk subunit F was determined by NMR spectroscopy, revealing a distinct two-domain structure, with the N-terminal 78 residues and a flexible C-terminal part formed by the residues 79-101. The two domains are loosely associated, providing new insights into energy coupling between AO and A1. The subunit H is a component of one of the two peripheral stalks connecting the upper water soluble A1 ATPase and the membrane bound subcomplex AO. Small angle X-ray scattering (SAXS) was used to determine the first low-resolution structure of this molecule in solution. The protein is dimeric and has a boomerang-like shape, composed of two arms of 12.0 and 6.8 nm in length. NMR analysis together with cross-linking and mutagenesis experiments has shown that subunit H is divided into a C-terminal coiled-coil domain and an N-terminal domain formed by adjacent helices. The solution structure of the peptide comprising the last twenty amino acids of subunit H, H85-104, and cross linking analysis at the C-terminus of entire H subunit indicate that the C-terminus is important for the structure formation of subunit H. To understand how the N-terminal domain of H is formed, the solution NMR structure of H1-47 was solved, revealing an -helix between residues 15–42 and a flexible N-terminal stretch. The -helix includes a kink that would bring the two helices of the C-terminus into the coiled-coil arrangement. Subunit E is another essential peripheral stalk subunit in A1AO ATP synthase. To get into the details, the N-terminal structure of subunit E, the truncated construct E1–52 of M. jannaschii A1AO ATP synthase was solved by NMR spectroscopy. The structure indicates a possible helix-helix interaction with subunit H. NMR titration experiments were performed between full length / truncated domains of subunits E, H and F. The data provide for the first time, structural insights of subunits E, H and F and their arrangement within the A1AO ATP synthase.