Interaction of Ferredoxin:NADP⁺Oxidoreductase with Phycobilisomes and Phycobilisome Substructures of the CyanobacteriumSynechococcussp. Strain PCC 7002

Abstract

The enzyme ferredoxin-NADP(+) oxidoreductase (FNR) from Synechococcus sp. PCC 7002 has an extended structure comprising three domains (FNR-3D) (Schluchter, W. M., and Bryant, D. A. (1992) Biochemistry 31, 3092-3102). Phycobilisome (PBS) preparations from wild-type cells contained from 1.0 to 1.6 molecules of FNR-3D per PBS, with an average value of 1.3 FNR per PBS. A maximum of two FNR-3D molecules could be specifically bound to wild-type PBS via the N-terminal, CpcD-like domain of the enzyme when exogenous recombinant FNR-3D (rFNR-3D) was added. To localize the enzyme within the PBS, the interaction of PBS and their substructures with rFNR-3D was further investigated. The binding affinity of rFNR-3D for phycocyanin (PC) hexamers, which contained a 22-kDa proteolytic fragment derived from CpcG, the L(RC)(27) linker polypeptide, was higher than its affinity for PC hexamers containing no linker protein. PBS from a cpcD3 mutant, which lacks the 9-kDa, PC-associated rod linker, incorporated up to six rFNR-3D molecules per PBS. PBS of a cpcC mutant, which has peripheral rods that contain single PC hexamers, also incorporated up to six rFNR-3D molecules per PBS. Direct competition binding experiments showed that PBS from the cpcD3 mutant bound more enzyme than PBS from the cpcC mutant. These observations support the hypothesis that the enzyme binds preferentially to the distal ends of the peripheral rods of the PBS. These data also show that the relative affinity order of the PC complexes for FNR-3D is as follows: (alpha(PC)beta(PC))(6)-L(R)(33) > (alpha(PC)beta(PC))(6)-L(RC)(27) > (alpha(PC)beta(PC))(6). The data suggest that, during the assembly of the PBS, FNR-3D could be displaced to the periphery according to its relative binding affinity for different PC subcomplexes. Thus, FNR-3D would not interfere with the light absorption and energy transfer properties of PC in the peripheral rods of the PBS. The implications of this localization of FNR within the PBS with respect to its function in cyanobacteria are discussed.

Biogenesis of Phycobiliproteins

“…PCC 7002 were deduced from the complete genome sequence of this organism. 4 The nucleotide sequences of these three genes have been deposited in GenBank TM as accessions EU145731, EU145732, and EU145733. The amino acid sequence data of homologs of CpcS-I and CpeS proteins was obtained from the Integrated Microbial Genomes of the DOE Joint Genome Institute (img.jgi.doe.gov/cgi-bin/pub/main.cgi) and from CyanoBase.…”

“…PBS of the unicellular marine cyanobacterium Synechococcus sp. PCC 7002 have been extensively characterized biochemically (3)(4)(5)(6)(7)(8)(9)(10)(11). These PBS are assembled from rods containing two or three hexamers of phycocyanin (PC, ␣ PC 6 and ␤ PC 6 ) (4 -8) and a core containing three cylindrical subassemblies of allophycocyanin (AP) (9 -11).…”

CpcM Posttranslationally Methylates Asparagine-71/72 of Phycobiliprotein Beta Subunits in Synechococcus sp. Strain PCC 7002 and Synechocystis sp. Strain PCC 6803

“…strain PCC 7002 in considerable detail (5,6,11,12,18,19,23,38,48). More recently, we have been studying the posttranslational processes that lead to maturation of holo-PBP in this cyanobacterium.…”

A second isoform of the ferredoxin:NADP oxidoreductase generated by an in-frame initiation of translation

“…It was proposed that the FNR binds to the PBS rods via its linker domain to fulfill functions in both cyclic electron transport and respiration, in close proximity to the membrane (6,15). A Ϸ35-kDa FNR (similar in size to that of plastids) has been purified from several cyanobacterial strains, Spirulina sp.…”