Characterization of a b 2δ Complex fromEscherichia coli ATP Synthase

• Published in: The Journal of biological chemistry 1998-04, Vol.273 (15), p.8646
• Main Authors: Stanley D. Dunn, Jennifer Chandler
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.273.15.8646

The δ subunit of Escherichia coli ATP synthase has been expressed and purified, both as the intact polypeptide and as δ′, a proteolytic fragment composed of residues 1–134. The solution structure of δ′ as a five-helix bundle has been previously reported (Wilkens, S., Dunn, S. D., Chandler, J., Dahlquist, F. W., and Capaldi, R. A. (1997) Nat. Struct. Biol. 4, 198–201). The δ subunit, in conjunction with δ-depleted F 1 -ATPase, was fully capable of reconstituting energy-dependent fluorescence quenching in membrane vesicles that had been depleted of F 1 . A complex of δ with the cytoplasmic domain of the b subunit of F 0 was demonstrated and characterized by analytical ultracentrifugation using b ST34–156 , a form of the b domain lacking aromatic residues. Molecular weight determination by sedimentation equilibrium supported a b 2 δ subunit stoichiometry. The sedimentation coefficient of the complex, 2.1 S, indicated a frictional ratio of approximately 2, suggesting that δ and the b dimer are arranged in an end-to-end rather than side-by-side manner. These results indicate the feasibility of the b 2 δ complex reaching from the membrane to the membrane-distal portion of the F 1 sector, as required if it is to serve as a second stalk.