Reconstitution of bacterial photosynthetic unit in a lipid bilayer studied by single-molecule spectroscopy at 5 K

• DOI: 10.1039/c1cp20172g
• Publication Date: 2011-05-20T08:30:27Z
• Authors: Daisuke Uchiyama; Hiroyuki Oikawa; Kohei Otomo; Mamoru Nango; Takehisa Dewa; Satoru Fujiyoshi; Michio Matsushita
• Keywords: Cold Temperature; 570; Rhodopseudomonas; 0303 health sciences; 03 medical and health sciences; Spectrometry, Fluorescence; Energy Transfer; Lipid Bilayers; Light-Harvesting Protein Complexes; Rhodobacter sphaeroides; 540; Dimerization

As a model of photosynthetic unit (PSU), self-assembled aggregates of pigment-protein complexes from photosynthetic bacteria were prepared in a lipid bilayer by reconstitution of the light-harvesting 2 (LH2) complex and light-harvesting 1-reaction center (LH1-RC) complex through detergent removal of their micelles in the presence of lipids. By performing polarization-controlled fluorescence and fluorescence-excitation spectroscopy on single aggregates at a temperature of 5 K, the composition of individual aggregates was determined and excitation energy transfer (EET) between constituent complexes was observed. LH2 and LH1-RC from a bacterium, Rhodobacter (Rb.) sphaeroides, were found to form a trimeric aggregate in which EET takes place from one LH2 to two LH1-RCs. In contrast, a heterodimer of LH2 and LH1-RC in which EET works was found to assemble from a combination of complexes of different bacterial species, that is, LH2 from Rb. sphaeroides and LH1-RC from Rhodopseudomonas (Rps.) palustris.