Purification and characterization of the B808-866 light-harvesting complex from green filamentous bacterium Chloroflexus aurantiacus.
The integral membrane light-harvesting complex B808-866 from the thermophilic green filamentous bacterium Chloroflexus aurantiacus has been isolated and characterized. Reversed-phase HPLC analysis demonstrated that the number of bacteriochlorophyll (BChl) in the B808-866 antenna complex is 36 +/- 2 per reaction center. The main carotenoid type is gamma-carotene, and the molar ratio of BChl to carotenoid is 3:2. The steady-state absorption and fluorescence spectroscopy of the B808-866 complex are reminiscent of the well-studied LH2 peripheral antenna of purple bacteria, whereas the protein sequence and the circular dichroism spectrum of B808-866 is more similar to the LH1 inner core antenna. The efficiency of excitation transfer from carotenoid to BChl is about 25%. The above results combined with electron microscopy and dynamic light scattering analysis suggest that the B808-866 antenna is more like the LH1, whereas surrounds the reaction center but probably consists of 24 building blocks with a ring diameter of about 20 nm. The above results suggested that there are probably two reaction centers inside the ring of B808-866. The unique properties of this light-harvesting complex may provide insights on the protein-pigment interactions in bacterial photosynthesis.
Xin
Yueyong
Y
Department of Chemistry and Biochemistry and the Center for the Study of Early Events in Photosynthesis, Arizona State University, P.O. Box 871604, Tempe, AZ 85287-1604, USA.
Lin
Su
S
Montaño
Gabriel A
GA
Blankenship
Robert E
RE
D001426:Bacterial Proteins / Q000737:chemistry* / Q000302:isolation & purification* / Q000648:ultrastructure; D041861:Chloroflexus / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D008854:Microscopy, Electron; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000302:isolation & purification* / Q000648:ultrastructure; D013057:Spectrum Analysis
D001426:Bacterial Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; C069404:protein complex B806-866, Chloroflexus aurantiacus