Trapping of an assembly intermediate of photosynthetic LH1 antenna beyond B820 subunit. Significance for the assembly of photosynthetic LH1 antenna.
Most photosynthetic LH1 antennae undergo dissociation into B820 subunits, suggesting their universal character as structural modules. However, dissociation into subunits seems to occur reversibly only in the absence of carotenoids and the subunits were never found to bind carotenoids. The interactions of carotenoids with B820 have been studied in a newly developed reconstitution assay of the LH1 antenna from Rhodospirillum rubrum (Fiedor, L., Akahane, J., and Koyama, Y. (2004) Biochemistry 43, 16487-16496). These model studies show that B820 subunits strongly interact with carotenoids and spontaneously form stable LH1-like complexes with substoichiometric carotenoid content. This is the first experimental evidence that B820 may occur as a short-lived intermediate in the assembly of LH1 in vivo. The resulting complex of B820 subunits with carotenoid, termed iB873, is homogeneous, according to ion exchange chromatography and reproducible pigment composition. The iB873-bound carotenoid is as efficient in energy transfer to bacteriochlorophyll as the one in native antenna. To our knowledge, iB873 is the first complex binding functional carotenoid, with the spectral and biochemical properties intermediate between that of B820 and the fully assembled LH1.
Fiedor
Leszek
L
Faculty of Biotechnology, Jagiellonian University, PL-30387 Cracow, Poland. lfiedor@mol.uj.edu.pl
Scheer
Hugo
H
D000096:Acetone / Q000737:chemistry / Q000494:pharmacology; D001426:Bacterial Proteins / Q000378:metabolism / Q000502:physiology*; D001429:Bacteriochlorophylls / Q000378:metabolism; D002338:Carotenoids / Q000378:metabolism; D002852:Chromatography, Ion Exchange; D002856:Chromatophores; D002942:Circular Dichroism; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism / Q000502:physiology*; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism; D010860:Pigments, Biological; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012247:Rhodospirillum rubrum / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry
D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D010860:Pigments, Biological; C094744:light-harvesting complex 1, Rhodospirillum; D000096:Acetone; D002338:Carotenoids