Methionine oxidation and its effect on the stability of a reconstituted subunit of the light-harvesting complex from Rhodospirillum rubrum.
An additional component in the purified core light-harvesting complex (LH1) from wild-type purple photosynthetic bacterium Rhodospirillum rubrum has been identified as an oxidized species of alpha-polypeptide by MALDI-TOF mass spectrometry. This component appears as a slightly earlier-eluting peak in the RP-HPLC chromatogram compared with the authentic alpha-polypeptide. The oxidation site has been determined to be the N-terminal methionine residue by high-resolution NMR spectroscopy, where the methionine is oxidized to methionine sulfoxide in a diastereoisomeric form. Interconversion between the oxidized and authentic alpha-polypeptides has been confirmed by selective oxidation and reduction. The oxidative modification of methionine is shown to have discernible effects on the ability to form B820 subunit with beta-polypeptide and bacteriochlorophyll a, and on the stability of the reconstituted B820 subunit. Both the ability and the stability for the samples using the oxidized alpha-polypeptide are moderately reduced, indicating that the oxidation-induced conformational change in the N-terminal domain of alpha-polypeptide may affect the pigment-binding environment through a long-range interaction. The MALDI-TOF mass results also reveal that the N-terminus of alpha-polypeptide is formylated and no phosphorylation has occurred in this polypeptide.
Wang
Z Y
ZY
Department of Biomolecular Engineering, Faculty of Engineering, Center for Interdisciplinary Research, Tohoku University, Sendai, Japan. wang@biophys.che.tohoku.ac.jp
Shimonaga
M
M
Muraoka
Y
Y
Kobayashi
M
M
Nozawa
T
T
D002851:Chromatography, High Pressure Liquid; D045342:Light-Harvesting Protein Complexes; D008715:Methionine / Q000378:metabolism*; D019906:Nuclear Magnetic Resonance, Biomolecular; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D012247:Rhodospirillum rubrum / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D008715:Methionine