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.

The 7.5-Å Electron Density and Spectroscopic Properties of a NovelLow-Light B800 LH2 from Rhodopseudomonas palustris

“…Our calculations suggest four Bchl a molecules per repeating unit in LL B800, and not three as determined for B800 -850 complexes. A Bchl a/peptide ratio of 4.5 has been reported for the B830 LH2 complex of Chromatium purpuratum (Kerfeld et al, 1994), a purple sulfur bacterium which is believed to be evolutionarily more ancient than the purple nonsulfur bacteria. B830 LH2 from Chr.…”

Gene sequencing and characterization of the light-harvesting complex 2 from thermophilic purple sulfur bacterium Thermochromatium tepidum

“…In Chromatium (Chr.) purpuratum, three pairs of the LH2 ab polypeptides were isolated and partially sequenced (Kerfeld et al 1994). Interestingly, the LH2 from this bacterium shows a single spectral form characterized by a strong absorption peak at 830 nm with a shoulder at 802 nm , and this spectral form was unchangeable by modifying growth conditions.…”

Isolation and Characterization of Soluble Electron Transfer Proteins from Chromatium purpuratum

“…(A) Cell Growth and Protein Preparation. Cells of C. purpuratum obtained from 152 L of culture (yielding 300 g wet weight) were fractionated into a membrane and soluble fraction as previously described (Kerfeld et al, 1994a). The soluble fraction (with an OD 280 of 0.888) was filtered to remove particulates and dialyzed against 20 mM Tris-HCl, pH 8.0; 350 mL was adsorbed to a Pharmacia XK26/20 column packed with 80 mL of Whatman DE-52 DEAEcellulose anion exchange resin (Fisher Scientific, Tustin, CA) and equilibrated in 20 mM Tris-HCl, pH 8.0, containing 0.01% NaN 3 (buffer A) at a flow rate of 5.5 mL/min.…”