Unexpected similarities of the B800-850 light-harvesting complex from Rhodospirillum molischianum to the B870 light-harvesting complexes from other purple photosynthetic bacteria.
The B800-850 light-harvesting complex (also called LH2) was isolated from photosynthetic membranes of Rhodospirillum molischianum DSM 119 using molecular sieve and ion-exchange chromatography. Its two bacteriochlorophyll a-binding polypeptides (alpha-subunit and beta-subunit) were purified with a reverse-phase HPLC system. The complete amino acid sequences of both subunits have been determined. The alpha- and beta-subunits consist of 56 and 45 amino acids, respectively, corresponding to molecular weights of 5939 and 5133. In contrast to the B800-850 complexes from other photosynthetic bacteria, the native B800-850 complex from Rs. molischianum is most likely an octamer of monomers with a stoichiometry of three bacteriochlorophyll a and 1.5 lycopenes per alpha,beta-subunit. Resonance Raman spectra provide evidence for a 5-coordinated Mg2+ in the BChl, and a carotenoid mainly in the all-trans configuration. A comparison between resonance Raman data from different photosynthetic bacteria indicates that the BChl a-binding site of the B800-850 complex from Rs. molischianum is more similar to the B870 complexes (also called LH1) than to the B800-850 complexes of other photosynthetic bacteria. Sequence similarities especially between the beta-subunits of the B800-850 complex of Rs. molischianum and the B870 and B800-850 complexes of other photosynthetic bacteria agree with this result and provide information on the mode of pigment binding in bacterial antenna complexes.
Max-Planck-Institut für Biophysik, Abteilung Molekulare, Frankfurt, FRG.
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L
Germeroth
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F
Lottspeich
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B
Robert
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H
Michel
D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D001436:Bacteriorhodopsins / Q000737:chemistry*; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D005583:Fourier Analysis; D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000302:isolation & purification; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000302:isolation & purification; D011487:Protein Conformation; D012246:Rhodospirillum / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013059:Spectrum Analysis, Raman
C081521:B800-850 light-harvesting complex, bacteria; D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances; D010446:Peptide Fragments; D045322:Photosynthetic Reaction Center Complex Proteins; D001436:Bacteriorhodopsins