Disease relevance of petA

• The difference in apparent molecular mass was maintained after expression of petA from both Chlamydomonas species in either E. coli or a C. reinhardtii DeltapetA mutant and after substitution of a unique third cysteine-292 to phenylalanine in the psychrophilic cytochrome f [1].
• The structure of cytochrome f includes an internal chain of five water molecules and six hydrogen-bonding side chains, which are conserved throughout the phylogenetic range of photosynthetic organisms from higher plants, algae, and cyanobacteria [2].

High impact information on petA

• The middle part of the Tbc2 protein displays partial amino acid sequence identity with Crp1, a protein from Zea mays that is implicated in the processing and translation of the chloroplast petA and petD RNAs [3].
• To this end, we have constructed three deletion mutant strains, each lacking one of the major chloroplast pet genes: the delta petA, delta petB and delta petD strains were unable to synthesize cyt f, cyt b6 and subunit IV (suIV) respectively [4].
• We have used a genetic approach to characterize the translocation of Chlamydomonas cytochrome f, a chloroplast-encoded protein that spans the thylakoid once [5].
• Cytochrome f accumulated to detectable levels in all mutant strains except the one with a UUC codon, but only the mutant with an AUU codon grew well at 24 degrees C under conditions that require photosynthesis [6].
• When expressed from a chimeric mRNA containing the atpA 5' untranslated region, cytochrome f no longer showed an assembly-dependent regulation of translation [7].

Biological context of petA

• Nucleotide sequences of the continuous and separated petA, petB and petD chloroplast genes in Chlamydomonas reinhardtii [8].
• We have mapped and sequenced the petA (cytf), petB (cytb6) and petD (subunit IV) genes on the chloroplast genome of Chlamydomonas reinhardtii [8].
• A dominant mutant allele at this locus, sim30-1d, was found to increase the translation initiation rate of the mutant petD mRNA. sim30-1d was also able to suppress the translational defect caused by an AUG to AUC mutation in the petD gene, and an AUG to AUU mutation in the chloroplast petA gene [9].
• We recovered one chloroplast suppressor in which the coding region of petA was now expressed under the control of a duplicated 5' untranslated region from another open reading frame of presently unknown function [10].
• To determine whether this stem-loop was required for petA mRNA stability, a series of deletions was constructed [11].

Anatomical context of petA

• In contrast, there was a decrease in polysome association of the polycistronic petA mRNA in the DeltapetB and DeltapetD mutants, suggesting that the synthesis of cytochrome f may be decreased in the absence of cytochrome b6 or SUIV [12].
• Thylakoids of N-limited cells have reduced amounts of cytochrome b6, cytochrome f, and light-harvesting complexes [13].
• Among the new polypeptides specifically found in the gametes, we detected a soluble polypeptide M alpha (approximate molecular mass of 63 kDa), which shared common epitopes with cytochrome f [14].
• Here, we show that M alpha is not a modification product of cytochrome f, but is part of protein M, a high-molecular-mass L-amino-acid oxidase located in the periplasm [15].
• Genetic analyses of Chlamydomonas reinhardtii ccs mutants, which are pleiotropically deficient in both the membrane-anchored cytochrome f and the soluble cytochrome c6, revealed a minimum of six loci, plastid ccsA and nuclear CCS1 through CCS5, that are required for the conversion of the chloroplast apocytochromes to their respective holo forms [16].

Associations of petA with chemical compounds

• C. reinhardtii and S. obliquus complexes contain the Rieske iron-sulfur protein (present in approx 1:1 molar ratio to cytochrome f) and each catalyzes a DBMIB- and DNP-INT-sensitive electron transfer from duroquinol to spinach plastocyanin [17].
• Its operation has been described by the "Q-cycle." This model proposes that electrons are transferred from plastoquinol to plastocyanin (the reductant of P700 in Photosystem I) through, obligatorily in series, the iron-sulfur and the cytochrome f redox centers in the cytochrome b(6)f complex [18].
• The N-terminal tyrosine of cytochrome f, which provides the sixth ligand to the heme group, has been changed by site-directed mutagenesis in Chlamydomonas reinhardtii to evaluate the role of this amino acid in assembly and function [19].
• The oxidation equivalents from Photosystem I are delivered to the high potential chain of the cytochrome b(6)f complex both at the cytochrome f level and, independently, at another site connected to the quinol-oxidizing site, possibly the iron-sulfur center [18].
• The reduction of the potential by either decreasing the light intensity or by adding increasing concentrations of the ionophore carbonylcyanide p-(trifluoromethoxy)phenylhydrazone (FCCP) revealed a marked inhibition of the cytochrome b(6) oxidation rate (10-fold) without substantial modifications of cytochrome f oxidation kinetics [20].

Physical interactions of petA

• Highly purified preparations of cytochrome b6 f complex from the unicellar freshwater alga Chlamydomonas reinhardtii contain about 1 molecule of chlorophyll a/cytochrome f [21].

Regulatory relationships of petA

• This 66-kDa polypeptide reacts with antibodies to cytochrome f and accumulates in gametes only in conditions that promote destabilisation of the cytochrome b6/f complex [15].

Other interactions of petA

• The resulting homoplasmic petG deletion strains are unable to grow photosynthetically, and immunoblot analysis shows markedly decreased levels of cytochrome b6, cytochrome f, the Rieske iron-sulfur protein, and subunit IV [22].
• Synthetic RNAs of the petA 3' UTR and the antisense strand of atpB 3' UTR were degraded in the extract [23].
• However, the C. reinhardtii petA transformants accumulated lower levels of cytochrome b ( 6 ) /f complexes and exhibited lower light saturated rates of O(2) evolution than C. reinhardtii wild type [1].

Analytical, diagnostic and therapeutic context of petA

• The biosynthesis of cytochrome f is a multistep process which requires processing of the precursor protein and covalent ligation of a c-heme upon membrane insertion of the protein [24].
• Unfolding of oxidized and reduced cytochrome f by guanidine hydrochloride (GuHCl) was monitored by far-UV circular dichroism (CD), Soret absorption, and tyrosine emission: the same unfolding curves were obtained regardless of method [25].
• Although cytochrome f from the Antarctic psychrophile, Chlamydomonas raudensis UWO 241, exhibits a lower apparent molecular mass (34 kD) than that of the mesophile C. reinhardtii (41 kD) based on SDS-PAGE, both proteins are comparable in calculated molecular mass and show 79% identity in amino acid sequence [1].

References