Deeply Branching c sub(6)-like Cytochromes of Cyanobacteria super([dagger])

The cyanobacterium Synechococcus sp. PCC 7002 carries two genes, petJ1 and petJ2, for proteins related to soluble, cytochrome c sub(6) electron transfer proteins. PetJ1 was purified from the cyanobacterium, and both cytochromes were expressed with heme incorporation in Escherichia coli. The expresse...

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Bibliographic Details
Published in:Biochemistry (Easton) 2008-01, Vol.47 (20), p.5515-5522
Main Authors: Tamiola, Kamil, Bialek, Wojciech, Szczepaniak, Andrzej, Nelson, Matthew, Kallas, Toivo
Format: Article
Language:English
Subjects:
Cyanophyta
Escherichia coli
Synechococcus
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Summary:The cyanobacterium Synechococcus sp. PCC 7002 carries two genes, petJ1 and petJ2, for proteins related to soluble, cytochrome c sub(6) electron transfer proteins. PetJ1 was purified from the cyanobacterium, and both cytochromes were expressed with heme incorporation in Escherichia coli. The expressed PetJ1 displayed spectral and biochemical properties virtually identical to those of PetJ1 from Synechococcus. PetJ1 is a typical cytochrome c sub(6) but contains an unusual KDGSKSL insertion. PetJ2 isolated from E. coli exhibited absorbance spectra characteristic of cytochromes, although the alpha , beta , and gamma bands were red-shifted relative to those of PetJ1. Moreover, the surface electrostatic properties and redox midpoint potential of PetJ2 (pI 9.7; E sub(m,7) = 148 +/-1.7 mV) differed substantially from those of PetJ1 (pI 3.8; E sub(m,7) = 319 +/-1.6 mV). These data indicate that the PetJ2 cytochrome could not effectively replace PetJ1 as an electron acceptor for the cytochrome bf complex in photosynthesis. Phylogenetic comparisons against plant, algal, bacterial, and cyanobacterial genomes revealed two novel and widely distributed clusters of previously uncharacterized, cyanobacterial c sub(6)-like cytochromes. PetJ2 belongs to a group that is distinct from both c sub(6) cytochromes and the enigmatic chloroplast c sub(6A) cytochromes. We tentatively designate the PetJ2 group as c sub(6C) cytochromes and the other new group as c sub(6B) cytochromes. Possible functions of these cytochromes are discussed.
ISSN:0006-2960
DOI:10.1021/bi701973g