Disease relevance of cycA

• Evidence for two promoters for the cytochrome c2 gene (cycA) of Rhodobacter sphaeroides [1].
• In vitro, cycA P1 was recognized by an RNA polymerase holoenzyme fraction that transcribes several well-characterized Escherichia coli heat shock (sigma32) promoters [2].
• Second order kinetics of the reduction of cytochrome c2 by the ubiquinone cytochrome b-c2 oxidoreductase of Rhodopseudomonas sphaeroides [3].
• Light-induced oxidation of the primary electron donor P and of the secondary donor cytochrome c2 was studied in whole cells of Rhodospirillum rubrum in the presence of myxothiazole to slow down their reduction [4].
• Interaction between cytochrome c2 and reaction centers from purple bacteria [5].

High impact information on cycA

• The cytochrome c2-mediated re-reduction kinetics of P+ were comparable to those observed in the wild-type [6].
• 0. Mutants of cytochrome c2 included K12D (lysine 12 substituted by aspartate), K14E (lysine 14 substituted by glutamate), K32E (lysine 32 substituted by glutamate), and K14E/K32E (lysines 14 and 32 substituted by glutamates) [7].
• The Rhodobacter sphaeroides photosynthesis response regulator, PrrA, positively regulates cycA P2 expression [8].
• However, the extent of transcription activation by PrrA at cycA P2 in vivo is greater under anaerobic conditions [8].
• Deletion analysis has identified sequences within 73 bp upstream of the transcription initiation site that are required for the activation of cycA P2 by PrrA [8].

Chemical compound and disease context of cycA

• The role of cytochrome c(2), encoded by cycA, and cytochrome c(Y), encoded by cycY, in electron transfer to the nitrite reductase of Rhodobacter sphaeroides 2.4.3 was investigated using both in vivo and in vitro approaches [9].
• Role of specific lysine residues in binding cytochrome c2 to the Rhodobacter sphaeroides reaction center in optimal orientation for rapid electron transfer [10].
• To understand the determinants of redox potential and protein stability in c-type cytochromes, we have characterized two mutations to a highly conserved tyrosine group, tyrosine-75, of Rhodobacter capsulatus cytochrome c2 [11].
• Partial reversion of the electrogenic reaction in the ubiquinol: cytochrome c2-oxidoreductase of Rhodobacter sphaeroides chromatophores under neutral and alkaline conditions [12].
• In Rhodobacter sphaeroides, cytochrome c2 (cyt c2) is a periplasmic redox protein required for photosynthetic electron transfer. cyt c2-deficient mutants created by replacing the gene encoding the apoprotein for cyt c2 (cycA) with a kanamycin resistance cartridge are photosynthetically incompetent [13].

Biological context of cycA

• DNA sequence analysis of the cycA gene indicated the presence of a typical procaryotic 21-residue signal sequence, suggesting that this periplasmic protein is synthesized in vivo as a precursor [14].
• Approximately 500 base pairs of DNA upstream of the cycA gene was sufficient to allow expression of this gene product in vitro [14].
• Synthesis of an immunoreactive cytochrome c2 precursor protein (Mr 15,500) was observed in vitro when plasmids containing the cycA gene were used as templates in an R. sphaeroides coupled transcription-translation system [14].
• The difference in gene organization relative to pucBAC and cycA suggests that this region originated independently of the photosynthesis gene cluster of R.sphaeroides [15].
• A detailed analysis of the gene organization in the photosynthesis region revealed a similar gene order in both species with some notable differences located to the pucBAC = cycA region [15].

Anatomical context of cycA

• Flash-induced electron transfer kinetics measured using whole cells demonstrated that the water-soluble cytochrome c1 is competent as a reductant for cytochrome c2 within the periplasmic space [16].
• Membranes deficient in cytochrome c2 were used for photo-oxidation studies, with and without the addition of purified cytochrome c2 [17].
• The influence of transmembrane potentials of the redox equilibrium between cytochrome c2 and the reaction center in Rhodopseudomonas sphaeroides chromatophores [18].
• Cytochrome c2 is located in vivo in the periplasmic space between the cell was and the cell membrane, and when chromatophores are prepared from whole cells the cytochrome becomes trapped inside these vesicles [19].
• It is expected that the electrogenic cyclic redox chain in the bacterial chromatophores incubed under conditions of continuous illumination may function at two regimes: (1) as a complete chain involving all the redox components, and (2) as a shortened chain involving only the P-870 photoreaction center, ubiquinone and cytochrome c2 [20].

Associations of cycA with chemical compounds

• However, phosphorylation of PrrA increased its activity since activation of cycA P2 was enhanced up to 15-fold by treatment with the low-molecular-weight phosphodonor acetyl phosphate [21].
• A single missense mutation which substitutes an Arg for a Cys at residue 182 of ChrR (C182R) was shown to be necessary and sufficient for the increased cycA transcription seen in the mutant strain Chr4 [22].
• A model is presented to explain why the presence of a functional DMSO reductase (DorA) is required for DMSO to decrease cycA P2 expression under photosynthetic conditions [23].
• Genes encoding bacteriochlorophyll (Bchl)-binding proteins (pufBALMX, pucBA, and puhA), cytochrome c2 (cycA), and enzymes involved in Bchl (bch) and carotenoid (crt) biosynthesis have been shown to reside within a contiguous 53-kb region of the R. sphaeroides DNA present on pWS2 [24].
• Cytochrome c2 was treated with chlorodinitrobenzoic acid to modify lysine amino groups to negatively charged carboxydinitrophenyllysines and separated into eight different fractions by ion-exchange chromatography on a Whatman SE 53 (sulfoxyethyl)cellulose column [25].

Regulatory relationships of cycA

• Analysis of a defined chrR null mutation indicated that this protein positively regulated cycA transcription [22].
• When cytochrome cy is expressed in R. sphaeroides in the presence of cytochrome c2, there is an increase in the amount of photo-oxidizable c-type cytochrome [26].

Other interactions of cycA

• The photosynthesis gene cluster is located within a approximately 73 kb Ase I genomic DNA fragment containing the puf, puhA, cycA and puc operons [15].
• A mutation responsible for uncoupling cycA transcription from tetrapyrrole availability was localized to a gene (chrR) that encodes a 357-amino-acid protein [22].
• The Rhodobacter sphaeroides ECF sigma factor, sigma(E), and the target promoters cycA P3 and rpoE P1 [27].
• While RpoH(I) reconstituted with R. sphaeroides core RNA polymerase transcribed all six promoters, RpoH(II) produced detectable transcripts from only four promoters (cycA P1, groESL(1), hslO, and ecfE) [28].
• These suppressors lacked detectable cyt c2, but they contained a new soluble cytochrome which was designated isocytochrome c2 (isocyt c2) that was not detectable in either cycA+ or cycA mutant cells [13].

Analytical, diagnostic and therapeutic context of cycA

• Northern blot analysis with an internal cycA-specific probe identified at least two possibly monocistronic transcripts present in both different cellular levels and relative stoichiometries in steady-state cells grown under different physiological conditions [14].
• Southern blot analysis confirmed that the wild-type cyc operon was exchanged for the inactivated cycA gene, presumably by double-reciprocal recombination [29].
• Study of the cytochrome c2-reaction center interaction by site-directed mutagenesis [7].
• Crystallization and preliminary X-ray diffraction analysis of cytochrome c2 from Rhodobacter sphaeroides [30].
• Potentiometric titration at A552--A540 showed the presence of two components that fitted an n = 1 titration; one component had a midpoint redox potential of +345mV, like cytochrome c2 in solution, and the second had E0' at pH 7.0 of +110 mV, and they were present in a ratio of approx. 2:3 [31].

References