Journal of Biochemistry Advance Access originally published online on February 5, 2007
Journal of Biochemistry 2007 141(3):411-420; doi:10.1093/jb/mvm045
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© 2007 The Japanese Biochemical Society.
Biophysics and Bioinformatics Reveal Structural Differences of the Two Peripheral Stalk Subunits in Chloroplast ATP Synthase
1Lehrstuhl für Biochemie der Pflanzen, Ruhr-Universität Bochum, Universitätsstr. 150, D-44801 Bochum, Germany; 2Forschungszentrum Jülich, IBI-2: Structural Biology, D-52425 Jülich, Germany; 3Institute of Biophysics, J. W. von Goethe-Universität, Theodor-Stern-Kai 7, D-60590 Frankfurt/Main, Germany; and 4Department of Chemistry, Physical Biochemistry, Darmstadt University of Technology, Petersenstrasse 22, D-64287 Darmstadt, Germany
To whom correspondence should be addressed. Tel: +49-234-32-24535, Fax: +49-234-32-14322, E-mail: ansgar.poetsch{at}ruhr-uni-bochum.de
Correspondence may also be addressed: Tel: +49-6151-16-5193, Fax: +49-6151-16-4171, E-mail: seelert{at}hrzpub.tu-darmstadt.de
Received November 2, 2006; Accepted January 17, 2007
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Abstract |
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ATP synthases convert an electrochemical proton gradient into rotational movement to produce the ubiquitous energy currency adenosine triphosphate. Tension generated by the rotational torque is compensated by the stator. For this task, a peripheral stalk flexibly fixes the hydrophilic catalytic part F1 to the membrane integral proton conducting part FO of the ATP synthase. While in eubacteria a homodimer of b subunits forms the peripheral stalk, plant chloroplasts and cyanobacteria possess a heterodimer of subunits I and II. To better understand the functional and structural consequences of this unique feature of photosynthetic ATP synthases, a procedure was developed to purify subunit I from spinach chloroplasts. The secondary structure of subunit I, which is not homologous to bacterial b subunits, was compared to heterologously expressed subunit II using CD and FTIR spectroscopy. The content of 
-helix was determined by CD spectroscopy to 67% for subunit I and 41% for subunit II. In addition, bioinformatics was applied to predict the secondary structure of the two subunits and the location of the putative coiled–coil dimerization regions. Three helical domains were predicted for subunit I and only two uninterrupted domains for the shorter subunit II. The predicted length of coiled–coil regions varied between different species and between subunits I and II.
Key Words: bioinformatics, CD spectroscopy, dimerization, FOF1, FTIR
Abbreviations: CD, circular dichroism; CFOF1, proton translocating ATP synthase of chloroplasts; CHAPS, 3-[(cholamidopropyl)dimethylammonio]-propanesulfonate; DTT, dithiothreitol; F1, hydrophilic part of ATP synthase; FO, hydrophobic, membrane integral part of ATP synthase
* Present address: University Bielefeld, Biophysical Chemistry PC III, D-33501 Bielefeld