Structural differences in chlorosomes from Chloroflexus aurantiacus grown under different conditions support the BChl c-binding function of the 5.7 kDa polypeptide

• Published in: FEBS letters Vol. 342; no. 3; pp. 319 - 324
• Main Authors: Lehmann, Rainer P., Brunisholz, René A., Zuber, Herbert
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 11-04-1994; Elsevier
• Subjects: Amino Acid Sequence; Bacteria - ultrastructure; Bacterial Proteins - metabolism; Bacteriochlorophyll c; Bacteriochlorophylls - metabolism; BChI, bacteriochlorophyll; Biological and medical sciences; CD, circular dichroism; Cell structures and functions; Chloroflexus aurantiacus; Chloroplast, photosynthetic membrane and photosynthesis; Circular Dichroism; CM, cytoplasmic membrane; Endopeptidase K; Fundamental and applied biological sciences. Psychology; Green photosynthetic bacterium; Light-harvesting antenna; Molecular and cellular biology; Molecular Sequence Data; Photosynthesis; Pigment-protein interaction; Protein Binding; Serine Endopeptidases - pharmacology; Spectrum Analysis; Trypsin - pharmacology; BChI, bacteriochlorophyll; CM, cytoplasmic membrane; Pigment-protein interaction; Bacteriochlorophyll c; Light-harvesting antenna; Green photosynthetic bacterium; Circular dichroism; CD, circular dichroism; Stoichiometry; Light harvesting system; Photosynthetic pigment; Polypeptide; Chloroflexus aurantiacus; Bacteria; Molecular interaction; Structural analysis; Bacteriochlorophyll a
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1016/0014-5793(94)80524-5

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 BChI
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 (
ΔA/A
740) 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.