title: Structural differences in chlorosomes from Chloroflexus aurantiacus grown under different conditions support the BChl c-binding function of the 5.7 kDa polypeptide.
abstract: Structurally different chlorosomes were isolated from the green photosynthetic bacterium Chloroflexus aurantiacus grown under different conditions. They were analysed with respect to variable pigment-protein stoichiometries in view of the presumed BChl c-binding function of the 5.7 kDa chlorosome polypeptide. Under high-light conditions on substrate-limited growth medium the pigment-protein ratio of isolated chlorosomes was several times lower than under low-light conditions on complex medium. Proteolytic degradation of the 5.7 kDa polypeptide in high-light chlorosomes led to a 60% decrease of the absorbance at 740 nm. The CD spectrum of high-light chlorosomes exhibited a sixfold lower relative intensity at 740 nm (delta A/A740) than low-light chlorosomes, but it showed a fivefold increase in intensity upon degradation of the 5.7 kDa polypeptide compared to a twofold increase in low-light chlorosomes. It seems probable that BChl c in the chlorosomes is present as oligomers bound to the 5.7 kDa polypeptide. Our data suggest further that compared to low-light chlorosomes smaller oligomers or single BChl c molecules are bound to the 5.7 kDa polypeptide in high-light chlorosomes resulting in lower rotational strength.
authors.affiliation: Institut für Molekularbiologie und Biophysik, ETH-Hönggerberg, Zürich, Switzerland.
authors.forename: R P
authors.initials: RP
authors.lastname: Lehmann
authors.forename: R A
authors.initials: RA
authors.lastname: Brunisholz
authors.forename: H
authors.initials: H
authors.lastname: Zuber
mesh_terms: D000595:Amino Acid Sequence; D001419:Bacteria / Q000648:ultrastructure*; D001426:Bacterial Proteins / Q000378:metabolism; D001429:Bacteriochlorophylls / Q000378:metabolism*; D002942:Circular Dichroism; D019286:Endopeptidase K; D008969:Molecular Sequence Data; D010788:Photosynthesis; D011485:Protein Binding; D012697:Serine Endopeptidases / Q000494:pharmacology; D013057:Spectrum Analysis; D014357:Trypsin / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D012697:Serine Endopeptidases; D014357:Trypsin; D019286:Endopeptidase K