Localization of the delta subunit in the Escherichia coli F1F0-ATPsynthaseby immune electron microscopy: The subunit delta binds on top of the F-1

The binding site of the delta subunit in the F1F0-ATPsynthase from Escheric hia coil has been determined by electron microscopy of negatively stained, antibody-decorated enzyme molecules. The images show that the antibody is b ound at the very top of the F-1 domain indicating that at least part of del ta is bound in the dimple formed by the N termini of the alpha and beta sub units. The data may explain why there is only one binding site for delta or e the F-1 despite there being three identical alpha beta pairs. The finding also implies that the b subunits of the F-0 have to extend all the way fro m the membrane surface to the very top of the F-1 domain to make contact wi th the delta subunit. (C) 2000 Academic Press.