Cytochrome f and subunit IV, two essential components of the photosynthetic bf complex typically encoded in the chloroplast genome, are nucleus-encoded in Euglena gracilis (original) (raw)
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The Journal of biological chemistry, 1988
We have isolated and determined the nucleotide and derived protein sequences for the four genes, petCA and BD, which encode the cytochrome b6-f, electron-transfer complex of the filamentous cyanobacterium, Nostoc PCC 7906. The primary structure and cotranscription of the petCA genes encoding the Rieske-FeS (nuclear encoded in plants) and apocytochrome f proteins has been described previously (Kallas, T., Spiller, S., and Malkin, R. (1988) Proc. Natl. Acad. Sci. U.S.A., in press). The petBD genes (645 and 480 protein-coding nucleotides, respectively) for the apocytochrome b6 (24.3 kDa) and subunit-IV (17.5 kDa) proteins comprise a second operon located at least 12 kilobases (kb) from petCA. The Nostoc petBD genes are not closely linked to the psbB gene (encoding the 51-kDa photosystem II polypeptide) and do not contain introns as do the closely related chloroplast genes. DNA probes specific for each of the Nostoc cytochrome-complex genes hybridized to single bands in genomic DNA blot...
Characterization of the Chloroplast Cytochrome b6f Complex as a Structural and Functional Dimer
Biochemistry, 1994
Size analysis of the cytochrome b 6 f complex by FPLC Superose-12 chromatography and Blue Native PAGE indicated a predominantly dimeric component with M r = (1.9-2.5) × 10 5. The true dimer molecular weight including bound lipid, but not detergent, was estimated to be 2.3 × 10 5. Size and shape analysis by negative-stain single-particle electron microscopy indicated that the preparation of dimeric complexes contains a major population that has a protein cross section 40% larger than the monomer, binds more negative stain, and has a geometry with a distinct 2-fold axis of symmetry compared to the monomeric complex. The dimeric species is more stable at higher ionic strength with respect to conversion to the monomeric species. SDS-PAGE of monomer and dimer preparations indicated that both contain the four major polypeptides in approximately equal stoichiometry and also contain the petG M r 4000 subunit. One bound chlorophyll a per monomer, part of the bound lipid, is present in monomer and dimer. The in vitro electron-transport activity (decyl-PQH 2 →PC-ferricyanide) of the separated dimer was comparable to that of the isolated b 6 f complex and was 4-5-fold greater than that of the monomer preparation, whose activity could be attributed to residual dimer. No difference in the properties of the dimer and monomer was detected by SDS-PAGE or redox difference spectrophotometry that could account for the difference in activities. However, the concentration of the Rieske [2Fe-2S] center was found by EPR analysis of the g y = 1.90 signal to be lower in the monomer fraction by a factor of 3.5 relative to the dimer. The presence of active dimer at high levels in the detergent-extracted b 6 f complex, the absence of activity in the monomer, and the absence of a monomer preparation that is not degraded in its spectral properties and activity suggest that the simplest inference is that the dimer is the active complex in the membrane. The possibility that cytochrome b 6 f and bc 1 are primitive trans-membrane-signaling complexes is noted.
The Plant Cell, 1991
The biosynthesis of the cytochrome b6f complex has been studied in a mutant, no. 1073, of Lemna perpusilla that contained less than 1% of the four protein subunits when compared with a wild-type strain. RNA gel blot analyses of the mutant indicated that the chloroplast genes for cytochrome f , cytochrome b6, and subunit IV (petA, petB, and petD, respectively) are transcribed and that the petB and petD transcripts undergo their normal processing. Analysis of polysomal polyA+ RNA indicated that the leve1 of translationally active mRNA for the nuclear-encoded Rieske Fe-S protein (petC) was reduced by >lOO-fold in the mutant. lmmunoprecipitation of in vivo labeled proteins indicated that both cytochrome f and subunit IV are synthesized and that subunit IV has a 10-fold higher rate of protein turnover in the mutant. These results are discussed in terms of the assembly of the cytochrome complex and the key role of the Rieske Fe-S protein in this process.
Higher Plant and Cyanobacterial Photosystem I: Connected Cytochrome Pathways
2016
Oxygenic photosynthesis is the principal converter of sunlight into chemical energy on earth. The conversion of solar energy is catalyzed by four multi-subunit membrane protein complexes: photosystem I (PSI), photosystem II (PSII), the cytochrome b6-f complex (cytb6f) and ATP-synthase (FOF1). These protein complexes are connected by soluble electron carriers that are vital not only for the proper function of ATP and NADPH production but also to render the system highly efficient in different organisms and various environments, some of which are quite harsh. While the main fabric of the membrane complexes is highly conserved, their surfaces and interaction with the soluble factors provide the specificity and fine regulation of the operating system. One of the prime examples for this phenomenon is the cyanobacterial photosynthetic electron transport chain that is situated alongside with respiratory complexes, yet it stays unique by virtue of the interacting soluble components. Cyanoba...