Structure of the Cytosolic Part of the Subunit b-Dimer of Escherichia coli FoF1-ATP Synthase
Tassilo Hornung 1, Oleg A Volkov 2, Tarek M.A. Zaida 2, Sabine Delannoy 3, John G. Wise 2 and Pia D Vogel 2*
1 Arizona State University
2 Southern Methodist University
3 Agence Française de Sécurité Sanitaire des Aliments
* To whom correspondence should be addressed. E-mail: pvogel{at}smu.edu.
Submitted on August 30, 2007
Revised on October 16, 2007
Accepted on 29 January 2008
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Abstract |
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The structure of the external stalk and its function in the catalytic mechanism of the FoF1-ATP synthase remains one of the important questions in bioenergetics. The external stalk has been proposed to be either a rigid stator that binds F1 or an elastic structural element that transmits energy from the small rotational steps of subunits c to the F1 sector during catalysis. We have employed here proteomics, sequence-based structure prediction, molecular modeling and electron spin resonance spectroscopy using site-directed spin labeling to understand the structure and interfacial packing of the E. coli b-subunit homodimer external stalk. Comparisons of bacterial, cyanobacterial and plant b subunits demonstrated little sequence similarity. Super-secondary structure predictions, however, show that all of the compared b-sequences have extensive heptad repeats suggesting that the proteins all are capable of packing as left-handed coiled coils. Molecular modeling subsequently indicated that b2 from the E. coli ATP synthase could pack into stable left-handed coiled coils. Thirty-eight substitutions to cysteine in soluble b-constructs allowed introduction of spin labels and the determination of inter-subunit distances by ESR. These distances correlated well with molecular modeling results and strongly suggest that the E. coli subunit b-dimer can stably exist as a left-handed coiled coil.
Key Words:
ATP-synthase, ESR, Site-specific spin labeling, coiled coils, stator subunits
