Quaternary Structure of V1 and F1 ATPase: Significance of Structural Homologies and Diversities

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Abstract
The V1 ATPase from the tobacco hornworm Manduca sexta and the Escherichia coli F1 ATPase were characterized by small-angle X-ray scattering (SAXS). The radii of gyration (Rg) of the complexes were 6.2 ± 0.1 and 4.7 ± 0.02 nm, respectively. The shape of the M. sexta V1 ATPase was determined ab initio from the scattering data showing six masses, presumed to be the A and B subunits, arranged in an alternating manner about a 3-fold axis. A seventh mass with a length of about 11.0 nm extends perpendicularly to the center of the hexameric unit. This central mass is presumed to be the stalk that connects V1 with the membrane domain (VO) in the intact V1VO-ATPase. In comparison, the shape of the F1 ATPase from E. coli possesses a quasi-3-fold symmetry over the major part of the enzyme. The overall asymmetry of the structure is given by a stem, assumed to include the central stalk subunits. The features of the V1 and F1 ATPase reveal structural homologies and diversities of the key components of the complexes.