High degree of organization of bacteriochlorophyll c in chlorosome-like aggregates spontaneously assembled in aqueous solution

Abstract

Pigment-lipid aggregates were formed in aqueous solution by diluting a chloroform/methanoll extract of chlorosomes of the green photosynthetic bacterium,3 Chlorobium limicola . The aggregates showed absorption and fluorescence spectra very similar to those of intact chlorosomes. No proteins were detected in the aggregates. Electron micrographs showed that the pigment-lipid aggregates were ellipsoidal bodies with average size of 130 nm along the long axis and 86 nm along the short axis. The linear dichroism spectrum of bacteriochlorophyll c in the pigment-lipid aggregates oriented in a stretched polyacrylamide gel was as strong as that in chlorosomes. These results suggest that spontaneous assembly of the protein-free pigments and lipids extracted from chlorosomes restores not only direct chromophore-chromophore interactions of bacteriochlorophyll c molecules but also the chlorosome-like higher-order structures.