Characterisation of subunit III and its oligomer from spinach chloroplast ATP synthase.
Proton ATP synthases carry out energy conversion in mitochondria, chloroplasts, and bacteria. A key element of the membrane integral motor CFO in chloroplasts is the oligomer of subunit III: it converts the energy of a transmembrane electrochemical proton gradient into rotational movement. To enlighten prominent features of the structure-function relationship of subunit III from spinach chloroplasts, new isolation methods were established to obtain highly pure monomeric and oligomeric subunit III in milligram quantities. By Fourier-transform infrared (FTIR) and CD spectroscopy, the predominantly alpha-helical secondary structure of subunit III was demonstrated. For monomeric subunit III, a conformational change was observed when diluting the SDS-solubilized protein. Under the same conditions the conformation of the oligomer III did not change. A mass of 8003 Da for the monomeric subunit III was determined by MALDI mass spectrometry (MALDI-MS), showing that no posttranslational modifications occurred. By ionisation during MALDI-MS, the noncovalent homooligomer III14 disaggregated into its III monomers.
Poetsch
Ansgar
A
Department of Chemistry, Physical Biochemistry, Darmstadt University of Technology, Petersenstrasse 22, D-64287 Darmstadt, Germany.
Rexroth
Sascha
S
Heberle
Joachim
J
Link
Thomas A
TA
Dencher
Norbert A
NA
Seelert
Holger
H
D025222:Chloroplast Proton-Translocating ATPases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D002942:Circular Dichroism; D017433:Protein Structure, Secondary; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D018724:Spinacia oleracea / Q000201:enzymology*
D025222:Chloroplast Proton-Translocating ATPases