title: Biophysics and bioinformatics reveal structural differences of the two peripheral stalk subunits in chloroplast ATP synthase.
abstract: 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 F(O) 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 alpha-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.
authors.affiliation: Lehrstuhl für Biochemie der Pflanzen, Ruhr-Universität Bochum, Universitätsstr. 150, D-44801 Bochum, Germany. ansgar.poetsch@ruhr-uni-bochum.de
authors.forename: Ansgar
authors.initials: A
authors.lastname: Poetsch
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Berzborn
authors.forename: Joachim
authors.initials: J
authors.lastname: Heberle
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Link
authors.forename: Norbert A
authors.initials: NA
authors.lastname: Dencher
authors.forename: Holger
authors.initials: H
authors.lastname: Seelert
mesh_terms: D000595:Amino Acid Sequence; D055592:Biophysical Phenomena; D001703:Biophysics; D025222:Chloroplast Proton-Translocating ATPases / Q000737:chemistry*; D019295:Computational Biology; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000737:chemistry*; D016415:Sequence Alignment; D017550:Spectroscopy, Fourier Transform Infrared; D018724:Spinacia oleracea / Q000201:enzymology
chemical_list: D021122:Protein Subunits; D025222:Chloroplast Proton-Translocating ATPases