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Crystall structure of a ferredoxin-dependent bilin reductase (4-20-2007) |
| Phytobilins are heme-derived linear tetrapyrroles that function as chromophores for the light-sensing phytochrome photoreceptors and the light-harvesting phycobiliproteins in photosynthetic organisms. Light absorption by phytochromes effects a structural rearrangement of their phytobilin chromophores, triggering a protein conformational change that initiates a signaling cascade responsible for altering many aspects of growth and development. In phycobiliproteins, by contrast, phytobilins function as antennae to absorb light energy and transfer it to photosynthetic reaction centers. Consequently, biosynthesis of these linear tetrapyrroles is crucial for environmental adaptation of these organisms. An enzyme family, ferredoxin-dependent bilin reductases (FDBRs), has been known to involve in the chromophore biosynthesis process. Research teams of Shih-Long Tu, J. Clark Lagarias (UC Davis) and Andrew J. Fisher (UC Davis) solved the crystal structure of a member of FDBRs, PcyA from Nostoc. sp. PCC7120. Combined structural information and biochemical data, they proposed a new catalytic mechanism for PcyA and also other members of the FDBR family that are widespread in photosynthetic organisms (Biochem. 46: 1484-1494, 2007). |
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| Photoprotective Role(s) of Cytochrome b559 in Photosystem II (4-10-2007) |
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| Cytochrome b559 (Cyt b559) is one of the essential components of the photosystem II (PSII) reaction center. Cyt b559 is a heme-bridged heterodimer protein that is comprised of a and b subunits (encoded by the psbE and psbF genes) of 9 and 4 kDa, respectively. Cyt b559 has been proposed to play an important role in the cyclic electron flow processes that protect PSII from light-induced damage during photoinhibitory conditions. However, the exact role(s) of cyt b559 in this cyclic electron transfer pathway(s) in PSII remains unclear. To study the exact role(s) of cyt b559, Hsiu-An Chu and coworkers have constructed and characterized a series of site-directed mutants, each carrying a single amino acid substitution of one of the heme axial-ligands, in the cyanobacterium Synechocystis sp. PCC6803. They identified two cyt b559 mutant strains, H22Ka and H22YbPS+, that assemble stable PSII reaction centers and grow photoautotrophically. This work is the first report of cyt b559 mutants having substitutions of an axial heme-ligands that retain the ability to grow photoautotrophically and to assemble stable PSII reaction centers. These two mutant strains and their PSII particles will facilitate further biophysical and biochemical studies designed to determine the exact role(s) of cyt b559 in the protection of PSII against light-induced damage under photoinhibitory conditions [CH Hung, JY Huang, YF Chiu and HA Chu, Biochimica et Biophysica Acta 1767 (2007) 686–693. Available online at www.sciencedirect.com]. |
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| Remodeling of root epidermal cells -- a cover highlight (4-2-2007) |
| Communication between adjacent cells is important for cell fate decisions in animal and plant cells. The current issue of "Biochemical Society Transactions" presents the outcome of a meeting on "Intercellular Signaling in Plants, held last year at the University of Sheffield, UK. The cover picture highlights the work of Wolfgang Schmidt's group on remodeling of root epidermal cells. |
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