title: Purification and characterization of the peripheral antenna of the purple-sulfur bacterium Chromatium purpuratum: evidence of an unusual pigment-protein composition.
abstract: The purification and characterization of the peripheral antenna and the preliminary characterization of a carotenoid-protein complex from the purple-sulfur bacterium Chromatium purpuratum are described. The peripheral antenna of C. purpuratum is unusual among purple bacteria in that it can be resolved by SDS-PAGE into six subunits, the largest number observed thus far for a spectrally pure antenna complex. N-terminal sequence analyses of these subunits suggest that they may have an additional bacteriochlorophyll-binding site located outside the transmembrane domain. The results of pigment-protein quantification are also consistent with additional pigment-binding sites in the C. purpuratum LH2. Furthermore, CD measurements and sequence analysis suggest the presence of considerable beta-type in addition to alpha-helical secondary structure. Thus, the secondary and quaternary structures of this complex differ significantly from light-harvesting complexes of other purple photosynthetic bacteria. A carotenoid-protein complex is also described; it is an apparent association of three proteins and carotenoid and is closely associated with the peripheral antenna. The purple-sulfur bacteria are evolutionarily older than the relatively better characterized purple-nonsulfur organisms. The phenotypic features described here of the C. purpuratum photosynthetic apparatus are related to those of other purple bacteria and green-sulfur bacteria and may reflect the evolutionary position of this organism.
authors.affiliation: Department of Biology, University of California, Los Angeles 90024.
authors.forename: C A
authors.initials: CA
authors.lastname: Kerfeld
authors.forename: T O
authors.initials: TO
authors.lastname: Yeates
authors.forename: J P
authors.initials: JP
authors.lastname: Thornber
mesh_terms: D000595:Amino Acid Sequence; D001429:Bacteriochlorophylls / Q000378:metabolism*; D001665:Binding Sites; D002338:Carotenoids / Q000378:metabolism*; D002844:Chromatium / Q000378:metabolism*; D045342:Light-Harvesting Protein Complexes; D008969:Molecular Sequence Data; D045322:Photosynthetic Reaction Center Complex Proteins / Q000302:isolation & purification* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D002338:Carotenoids