1lgh
From Proteopedia
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CRYSTAL STRUCTURE OF THE LIGHT-HARVESTING COMPLEX II (B800-850) FROM RHODOSPIRILLUM MOLISCHIANUM
Overview
BACKGROUND: The light-harvesting complexes II (LH-2s) are integral, membrane proteins that form ring-like structures, oligomers of alpha, beta-heterodimers, in the photosynthetic membranes of purple bacteria., They contain a large number of chromophores organized optimally for light, absorption and rapid light energy migration. Recently, the structure of, the nonameric LH-2 of Rhodopseudomonas acidophila has been determined; we, report here the crystal structure of the octameric LH-2 from, Rhodospirillum molischianum. The unveiling of similarities and differences, in the architecture of these proteins may provide valuable insight into, the efficient energy transfer mechanisms of bacterial photosynthesis., RESULTS: The crystal structure of LH-2 from Rs. molischianum has been, determined by molecular replacement at 2.4 A resolution using X-ray, diffraction. The crystal structure displays two concentric cylinders of, sixteen membrane-spanning helical subunits, containing two rings of, bacteriochlorophyll-a (BChl-a) molecules. One ring comprises sixteen B850, BChl-as perpendicular to the membrane plane and the other eight B800, BChl-as that are nearly parallel to the membrane plane; eight, membrane-spanning lycopenes (the major carotenoid in this complex) stretch, out between the B800 and B850 BChl-as. The B800 BChl-as exhibit a, different ligation from that of Rps. acidophila (aspartate is the Mg, ligand as opposed to formyl-methionine in Rps. acidophila). CONCLUSIONS:, The light-harvesting complexes from different bacteria assume various ring, sizes. In LH-2 of Rs. molischianum, the Qy transition dipole moments of, neighbouring B850 and B800 BChl-as are nearly parallel to each other, that, is, they are optimally aligned for Foster exciton transfer. Dexter energy, transfer between these chlorophylls is also possible through interactions, mediated by lycopenes and B850 BChl-a phytyl tails; the B800 BChl-a and, one of the two B850 BChl-as associated with each heterodimeric unit are in, van der Waals distance to a lycopene, such that singlet and triplet energy, transfer between lycopene and the BChl-as can occur by the Dexter, mechanism. The ring structure of the B850 BChl-as is optimal for light, energy transfer in that it samples all spatial absorption and emission, characteristics and places all oscillator strength into energetically low, lying, thermally accessible exciton states.
About this Structure
1LGH is a Protein complex structure of sequences from Phaeospirillum molischianum with , , and as ligands. Known structural/functional Sites: , , , , , , , , , , and . Full crystallographic information is available from OCA.
Reference
The crystal structure of the light-harvesting complex II (B800-850) from Rhodospirillum molischianum., Koepke J, Hu X, Muenke C, Schulten K, Michel H, Structure. 1996 May 15;4(5):581-97. PMID:8736556
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