Recent Progress on the LH1-RC Complexes of Purple Photosynthetic Bacteria

Abstract

Photosynthetic bacteria have been proven to be excellent model organisms because they own the relatively simplified model systems for us to study the reactions that occurs at the initial stage of photosynthesis, compared with the oxygen-evolving cyanobacteria, algae, and higher plants. In purple bacteria, there are usually two kinds of light-harvesting (LH) complexes, named LH1 and LH2, respectively. LH2 is the peripheral antenna complex, and LH1 is the core antenna complex that surrounds the reaction center (RC) to form the LH1-RC supercomplex. Solar energy is first absorbed by the LH complex and then transferred rapidly and efficiently to the RC, where the charge separation and electron transfer take place. Several high-resolution structures are available for the RC and LH2 for a long time; for LH1-RC complex, its structure was solved and improved to an atomic resolution recently with a thermophilic purple photosynthetic bacterium Thermochromatium tepidum. The high-resolution structure provided much more detailed structural information of this supercomplex including the arrangements of protein subunits, pigments, and cofactors; a much more intact RC complex due to the protection of LH1 complex; the detailed coordination of the Ca2+ ions in the LH1 that are important for the absorption maximum at 915 nm as well as for the enhanced thermostability; the possible ubiquinone exchange pathway in the closed LH1 ring and so on. In addition, the dynamic processes involved in this complex were also discussed. All these results greatly advance our understanding on the molecular mechanism of bacterial photosynthesis, which could be essential for designing artificial photoelectronic conversion materials with enhanced performance.