Defective energy coupling in delta-subunit mutants of Escherichia coli F1F0-ATP synthase.

Membrane vesicles from 13 strains carrying mutations in the C-terminal region of the delta-subunit of Escherichia coli F1F0-ATP synthase were characterized in respect to ATPase activity, ATP-driven proton-pumping, dicyclohexylcarbodiimide sensitivity of ATPase, and oxidative phosphorylation. The salient finding was that energy-coupling between F1 and F0 sectors of the enzyme is impaired by several of the mutations. The delta G150N mutant appeared completely uncoupled in vitro. The data emphasize the role of the C-terminal region of delta-subunit in integration of the proton conduction machinery in F0 with the three F1 catalytic sites. It is suggested that the C-terminal region of delta-subunit, speculatively located in the central region of the alpha 3 beta 3 hexagon, acts functionally at the interface between the helical domain of the stalk and the F1 subunits to relay conformational signals which alter the affinities of the catalytic sites for substrates and products.