In yeast, mammals, and land plants, mitochondrial F(1)F(O)-ATP synthase (complex V) is a remarkable enzymatic machinery that comprises about 15 conserved subunits. Peculiar among eukaryotes, complex V from Chlamydomonadales algae (order of chlorophycean class) has an atypical subunit composition of its peripheral stator and dimerization module, with nine subunits of unknown evolutionary origin (Asa subunits). In vitro, this enzyme exhibits an increased stability of its dimeric form, and in vivo, Chlamydomonas reinhardtii cells are insensitive to oligomycins, which are potent inhibitors of proton translocation through the F(O) moiety. In this work, we showed that the atypical features of the Chlamydomonadales complex V enzyme are shared by the other chlorophycean orders. By biochemical and in silico analyses, we detected several atypical Asa subunits in Scenedesmus obliquus (Sphaeropleales) and Chlorococcum ellipsoideum (Chlorococcales). In contrast, complex V has a canonical subunit composition in other classes of Chlorophytes (Trebouxiophyceae, Prasinophyceae, and Ulvophyceae) as well as in Streptophytes (land plants), and in Rhodophytes (red algae). Growth, respiration, and ATP levels in Chlorophyceae were also barely affected by oligomycin concentrations that affect representatives of the other classes of Chlorophytes. We finally studied the function of the Asa7 atypical subunit by using RNA interference in C. reinhardtii. Although the loss of Asa7 subunit has no impact on cell bioenergetics or mitochondrial structures, it destabilizes in vitro the enzyme dimeric form and renders growth, respiration, and ATP level sensitive to oligomycins. Altogether, our results suggest that the loss of canonical components of the complex V stator happened at the root of chlorophycean lineage and was accompanied by the recruitment of novel polypeptides. Such a massive modification of complex V stator features might have conferred novel properties, including the stabilization of the enzyme dimeric form and the shielding of the proton channel. In these respects, we discuss an evolutionary scenario for F(1)F(O)-ATP synthase in the whole green lineage (i.e., Chlorophyta and Streptophyta).

Delta-lactoferrin is a transcription factor, the expression of which is downregulated or silenced in case of breast cancer. It possesses antitumoral activities and when it is re-introduced in mammary epithelial cancer cell lines, provokes antiproliferative effects. It is posttranslationally modified and our earlier investigations showed that the O-GlcNAcylation/phosphorylation interplay plays a major role in the regulation of both its stability and transcriptional activity. Here, we report the covalent modification of delta-lactoferrin with the small ubiquitin-like modifier SUMO-1. Mutational and reporter gene analyses identified five different lysine residues at K13, K308, K361, K379 and K391 as SUMO acceptor sites. The SUMOylation deficient M5S mutant displayed enhanced transactivation capacity on a delta-lactoferrin responsive promoter, suggesting that SUMO-1 negatively regulates the transactivation function of delta-lactoferrin. K13, K308 and K379 are the main SUMO sites and among them, K308, which is located in a SUMOylation consensus motif of the NDSM-like type, is a key SUMO site involved in repression of delta-lactoferrin transcriptional activity. K13 and K379 are both targeted by other posttranslational modifications. We demonstrated that K13 is the main acetylation site and that favoring acetylation at K13 reduced SUMOylation and increased delta-lactoferrin transcriptional activity. K379, which is either ubiquitinated or SUMOylated, is a pivotal site for the control of delta-lactoferrin stability. We showed that SUMOylation competes with ubiquitination and protects delta-lactoferrin from degradation by positively regulating its stability. Collectively, our results indicate that multi-SUMOylation occurs on delta-lactoferrin to repress its transcriptional activity. Reciprocal occupancy of K13 by either SUMO-1 or an acetyl group may contribute to the establishment of finely regulated mechanisms to control delta-lactoferrin transcriptional activity. Moreover, competition between SUMOylation and ubiquitination at K379 coordinately regulates the stability of delta-lactoferrin toward proteolysis. Therefore SUMOylation of delta-lactoferrin is a novel mechanism controlling both its activity and stability.

Delta-lactoferrin (∆Lf) is a transcription factor belonging to the lactoferrin family, the expression of which inhibits cell proliferation and leads to Skp1 and DcpS gene transactivation. In this study, we showed that ∆Lf expression also induces cell death via apoptosis in HEK 293 and MCF7 cells using a cell viability assay and DNA fragmentation. Western blot analyses showed that apoptosis was caspase-9, 7 and 8 dependent. Proteolytic cleavage of the endonuclease PARP was significantly increased. The levels of expression of Bcl family members were detected by immunochemistry and showed that the Bcl-xl/Bax and Bcl-2/Bax protein ratios were decreased. We determined that the pro-apoptotic effects of ∆Lf are mainly mediated by the activation of the mitochondria-dependent death-signaling pathway. Apoptosis induction by ∆Lf is concomitant with increased cellular levels of Bax protein. Analysis of the Bax promoter region detected a ∆Lf response element located at -155 bp from the transcription start site. Both luciferase reporter gene and chromatin immunoprecipitation assays confirmed that ∆Lf interacts in vitro and in vivo specifically with this sequence. Its deletion, realized using directed mutagenesis, totally abolished ∆Lf transcriptional activity, identifying it as a ∆Lf-responsive element. These results indicate that the Bax gene is a novel ∆Lf target. Moreover we also showed that the O-GlcNAc/P interplay, which controls ∆Lf transcriptional activity, modulates Bax transactivation.

Two genes encoding cytochrome c oxidase subunits, Cox2a and Cox2b, are present in the nuclear genomes of apicomplexan parasites and show sequence similarity to corresponding genes in chlorophycean algae. We explored the presence of COX2A and COX2B subunits in the cytochrome c oxidase of Toxoplasma gondii. Antibodies were raised against a synthetic peptide containing a 14-residue fragment of the COX2A polypeptide and against a hexa-histidine-tagged recombinant COX2B protein. Two distinct immunochemical stainings localized the COX2A and COX2B proteins in the parasite's mitochondria. A mitochondria-enriched fraction exhibited cyanide-sensitive oxygen uptake in the presence of succinate. T. gondii mitochondria were solubilized and subjected to Blue Native Electrophoresis followed by second dimension electrophoresis. Selected protein spots from the 2D gels were subjected to mass spectrometry analysis and polypeptides of mitochondrial complexes III, IV and V were identified. Subunits COX2A and COX2B were detected immunochemically and found to co-migrate with complex IV; therefore, they are subunits of the parasite's cytochrome c oxidase. The apparent molecular mass of the T. gondii mature COX2A subunit differs from that of the chlorophycean alga Polytomella sp. The data suggest that during its biogenesis, the mitochondrial targeting sequence of the apicomplexan COX2A precursor protein may be processed differently than the one from its algal counterpart.

No abstract