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Phycobilisomes, the light‐harvesting complexes of cyanobacteria and red algae, are a resource for photosynthetic, photonic and fluorescence labeling elements. They cover an exceptionally broad spectral range, but the complex superstructure and assembly have been an obstacle. By replacing in Synechocystis sp. PCC 6803 the biliverdin reductases, we studied the role of chromophores in the assembly of the phycobilisome core. Introduction of the green‐absorbing phycoerythrobilin instead of the red‐absorbing phycocyanobilin inhibited aggregation. A novel, trimeric allophycocyanin (Dic‐APC) was obtained. In the small (110 kDa) unit, the two chromophores, phycoerythrobilin and phytochromobilin, cover a wide spectral range (550 to 660 nm). Due to efficient energy transfer, it provides an efficient artificial light‐harvesting element. Dic‐APC was generated in vitro by using the contained core‐linker, LC, for template‐assisted purification and assembly. Labeling the linker provides a method for targeting Dic‐APC. [ABSTRACT FROM AUTHOR]

Phycobilisomes, the light-harvesting complexes of cyanobacteria and red algae, contain two to four types of chromophores that are attached covalently to seven or more members of a family of homologous proteins, each carrying one to four binding sites. Chromophore binding to apoproteins is catalyzed by lyases, of which only few have been characterized in detail. The situation is complicated by nonenzymatic background binding to some apoproteins. Using a modular multiplasmidic expression-reconstitution assay in Escherichia coli with low background binding, phycobilin:cystein-84 biliprotein lyase (CpeS1) from Anabaena PCC7120, has been characterized as a nearly universal lyase for the cysteine-84-binding site that is conserved in all biliproteins. It catalyzes covalent attachment of phycocyanobilin to all allophycocyanin subunits and to cysteine-84 in the [beta]-subunits of C-phycocyanin and phycoerythrocyanin. Together with the known lyases, it can thereby account for chromophore binding to all binding sites of the phycobiliproteins of Anabaena PCC7120. Moreover, it catalyzes the attachment of phycoerythrobilin to cysteine-84 of both subunits of C-phycoerythrin. The only exceptions not served by CpeS1 among the cysteine-84 sites are the [alpha]-subunits from phycocyanin and phycoerythrocyanin, which, by sequence analyses, have been defined as members of a subclass that is served by the more specialized E/F type lyases. biliprotein biosynthesis | light-harvesting | photosynthesis | phycobilisome

Chromophore attachment to phytochrome AlphA of the cyanobacterium Anabaena sp.PCC 7120, as well as to N-and C-terminally truncated AphA is reported. Several methods of phytochrome reconstitution are addressed, including the autocatalytic assembly of apo phytochrome with free phycocyanobilin (PCB) and the chromophore transfer from phycocyanin (CPC) to apo phytochrome autocatalytically and in the presence of PCB:CpcA lyase (CpcE/F).

Research has been conducted on the phytochromes. The molecular changes of a phytochrome during red (gives) far-red and reverse photoreactions have been monitored via static infrared difference spectroscopy and the use of the assembled with a chromophore recombinant N-terminal fragment chemically modified at ring D or with a chromophore labeled with (super)18 O at the ring A carbonyl group is discussed.