Molecular architecture of Escherichia coli F1 adenosinetriphosphatase

The structure of the E. coli F1 ATPase (ECF1) has been studied by a novel combination of two specimen preparation and image analysis techniques. The molecular outline of the ECF1 was determined by three-dimensional reconstruction of images of negatively stained two-dimensional crystals of ECF1. Internal features were revealed by analysis of single particles of ECF1, preserved in their native state in a thin layer of amorphous ice, and examined by cryoelectron microscopy. Various projections of the unstained ECF1 were interpreted consistently with the three-dimensional structure in negative stain, yielding a more informative description of the enzyme than otherwise possible. Results show that the ECF1 is a roughly spherical complex approximately 90-100 A in diameter. Six elongated protein densities (the alpha and beta subunits, each approximately 90 A X approximately 30 A in size) comprise its hexagonally modulated periphery. At the center of the ECF1 is an aqueous cavity which extends nearly or entirely through the length of the complex. A compact protein density, located at one end of the hexagonal barrel and closely associated with one of the peripheral subunits, partially obstructs the central cavity.