Expression studies of two paralogous ppa genes encoding distinct Family I pyrophosphatases in marine unicellular cyanobacteria reveal inactivation of the typical cyanobacterial gene

PPA1 Regulates Systemic Insulin Sensitivity by Maintaining Adipocyte Mitochondria Function as a Novel PPARγ Target Gene

Downregulation of mitochondrial function in adipose tissue is considered as one important driver for the development of obesity-associated metabolic disorders. Inorganic pyrophosphatase 1 (PPA1) is an enzyme that catalyzes the hydrolysis of inorganic pyrophosphate to inorganic phosphate and is required for anabolism to take place in cells. Although alteration of PPA1 has been related to some diseases, the importance of PPA1 in metabolic syndromes has never been discussed. In this study, we found that global PPA1 knockout mice (PPA1^+/-) showed impaired glucose tolerance and severe insulin resistance under high-fat-diet feeding. In addition, impaired adipose tissue development and ectopic lipid accumulation were observed. Conversely, overexpression of PPA1 in adipose tissue by adeno-associated virus injection can partly reverse the metabolic disorders in PPA1^+/- mice, suggesting that impaired adipose tissue function is responsible for the metabolic disorders observed in PPA1^+/- mice. Mechanistic studies revealed that PPA1 acted as a PPARγ target gene to maintain mitochondrial function in adipocytes. Furthermore, specific knockdown of PPA1 in fat body of Drosophila led to impaired mitochondria morphology, decreased lipid storage, and made Drosophila more sensitive to starvation. In conclusion, for the first time, our findings demonstrate the importance of PPA1 in maintaining adipose tissue function and whole-body metabolic homeostasis.

Metagenomic Insights into Rhizospheric Microbiome Profiling in Lentil Cultivars Unveils Differential Microbial Nitrogen and Phosphorus Metabolism under Rice-Fallow Ecology

The plant rhizosphere interfaces an array of microbiomes related to plant growth and development. Cultivar-specific soil microbial communities with respect to their taxonomic structure and specific function have not been investigated explicitly in improving the adaptation of lentil cultivars under rice-fallow ecology. The present study was carried out to decipher the rhizosphere microbiome assembly of two lentil cultivars under rice-fallow ecology for discerning the diversity of microbial communities and for predicting the function of microbiome genes related to nitrogen (N) and phosphorus (P) cycling processes deploying high-throughput whole (meta) genome sequencing. The metagenome profile of two cultivars detected variable microbiome composition with discrete metabolic activity. Cyanobacteria, Bacteroidetes, Proteobacteria, Gemmatimonadetes, and Thaumarchaeota were abundant phyla in the “Farmer-2” rhizosphere, whereas Actinobacteria, Acidobacteria, Firmicutes, Planctomycetes, Chloroflexi, and some incompletely described procaryotes of the “Candidatus” category were found to be robustly enriched the rhizosphere of “Moitree”. Functional prediction profiles of the microbial metagenomes between two cultivars revealed mostly house keeping genes with general metabolism. Additionally, the rhizosphere of “Moitree” had a high abundance of genes related to denitrification processes. Significant difference was observed regarding P cycling genes between the cultivars. “Moitree” with a profuse root system exhibited better N fixation and translocation ability due to a good “foraging strategy” for improving acquisition of native P under the nutrient depleted rice-fallow ecology. However, “Farmer-2” revealed a better “mining strategy” for enhancing P solubilization and further transportation to sinks. This study warrants comprehensive research for explaining the role of microbiome diversity and cultivar–microbe interactions towards stimulating microbiome-derived soil reactions regarding nutrient availability under rice-fallow ecology.

Nitrogen starvation induces extensive changes in the redox proteome of Prochlorococcus sp. strain SS120

Very low nitrogen concentration is a critical limitation in the oligotrophic oceans inhabited by the cyanobacterium Prochlorococccus, one of the main primary producers on Earth. It is well known that nitrogen starvation affects redox homeostasis in cells. We have studied the effect of nitrogen starvation on the thiol redox proteome in the Prochlorococcus sp. SS120 strain, by using shotgun proteomic techniques to map the cysteine modified in each case and to quantify the ratio of reversibly oxidized/reduced species. We identified a number of proteins showing modified cysteines only under either control or N-starvation, including isocitrate dehydrogenase and ribulose phosphate 3-epimerase. We detected other key enzymes, such as glutamine synthetase, transporters and transaminases, showing that nitrogen-related pathways were deeply affected by nitrogen starvation. Reversibly oxidized cysteines were also detected in proteins of other important metabolic pathways, such as photosynthesis, phosphorus metabolism, ATP synthesis and nucleic acids metabolism. Our results demonstrate a wide effect of nitrogen limitation on the redox status of the Prochlorococcus proteome, suggesting that besides previously reported transcriptional changes, this cyanobacterium responds with post-translational redox changes to the lack of nitrogen in its environment.

Comparative biochemical and functional studies of family I soluble inorganic pyrophosphatases from photosynthetic bacteria

Soluble inorganic pyrophosphatases (inorganic diphosphatases, EC 3.6.1.1) were isolated and characterized from three phylogenetically diverse cyanobacteria--Synechocystis sp. PCC 6803, Anabaena sp. PCC 7120, and Pseudanabaena sp. PCC 6903--and one anoxygenic photosynthetic bacterium, Rhodopseudomonas viridis (purple nonsulfur). These enzymes were found to be family I soluble inorganic pyrophosphatases with c. 20 kDa subunits with diverse oligomeric structures. The corresponding ppa genes were cloned and functionally validated by heterologous expression. Cyanobacterial family I soluble inorganic pyrophosphatases were strictly Mg(2+)-dependent enzymes. However, diverse cation cofactor dependence was observed for enzymes from other groups of photosynthetic bacteria. Immunochemical studies with antibodies to cyanobacterial soluble inorganic pyrophosphatases showed crossreaction with orthologs of other main groups of phototrophic prokaryotes and suggested a close relationship with the enzyme of heliobacteria, the nearest photosynthetic relatives of cyanobacteria. A slow-growing Escherichia coli JP5 mutant strain, containing a very low level of soluble inorganic pyrophosphatase activity, was functionally complemented up to wild-type growth rates with ppa genes from diverse photosynthetic prokaryotes expressed under their own promoters. Overall, these results suggest that the bacterial family I soluble inorganic pyrophosphatases described here have retained functional similarities despite their genealogies and their adaptations to diverse metabolic scenarios.

Differential regulation of soluble and membrane-bound inorganic pyrophosphatases in the photosynthetic bacterium Rhodospirillum rubrum provides insights into pyrophosphate-based stress bioenergetics

Soluble and membrane-bound inorganic pyrophosphatases (sPPase and H(+)-PPase, respectively) of the purple nonsulfur bacterium Rhodospirillum rubrum are differentially regulated by environmental growth conditions. Both proteins and their transcripts were found in cells of anaerobic phototrophic batch cultures along all growth phases, although they displayed different time patterns. However, in aerobic cells that grow in the dark, which exhibited the highest growth rates, Northern and Western blot analyses as well as activity assays demonstrated high sPPase levels but no H(+)-PPase. It is noteworthy that H(+)-PPase is highly expressed in aerobic cells under acute salt stress (1 M NaCl). H(+)-PPase was also present in anaerobic cells growing at reduced rates in the dark under either fermentative or anaerobic respiratory conditions. Since H(+)-PPase was detected not only under all anaerobic growth conditions but also under salt stress in aerobiosis, the corresponding gene is not invariably repressed by oxygen. Primer extension analyses showed that, under all anaerobic conditions tested, the R. rubrum H(+)-PPase gene utilizes two activator-dependent tandem promoters, one with an FNR-like sequence motif and the other with a RegA motif, whereas in aerobiosis under salt stress, the H(+)-PPase gene is transcribed from two further tandem promoters involving other transcription factors. These results demonstrate a tight transcriptional regulation of the H(+)-PPase gene, which appears to be induced in response to a variety of environmental conditions, all of which constrain cell energetics.

A novel calcium-dependent soluble inorganic pyrophosphatase from the trypanosomatidLeishmania major

A single-copy gene IPP encoding a putative soluble inorganic pyrophosphatase (LmsPPase, EC 3.6.1.1) was identified in the genome of the parasite protozoan Leishmania major. The full-length coding sequence (ca. 0.8 kb) was obtained from genomic DNA by polymerase chain reaction (PCR) and cloned into an Escherichia coli expression vector, and was overexpressed for functional protein purification and characterization. The recombinant LmsPPase, purified to electrophoretic homogeneity by a two-step chromatography procedure, exhibited a predicted molecular mass of ca. 30 kDa. The enzyme has an absolute requirement for divalent cations, exhibits a pH optimum of 7.5-8.0 and does not hydrolyze polyphosphates or adenosine triphosphate (ATP). LmsPPase differs from previously studied soluble pyrophosphatases with respect to cation selectivity, Ca(2+) being far more effective than Mg(2+). Comparisons to known sPPases show a short N-terminal extension predicted to be a mitochondrial transit peptide, and changes in active-site residues and the neighboring region. Subcellular fractionation of L. major promastigotes suggests a mitochondrial localization. Molecular phylogenetic analysis indicates that LmsPPase is a highly divergent eukaryotic Family I sPPase, perhaps an ancestral class of eukaryotic sPPases functionally adapted to a calcium-rich, probably mitochondrial, environment.

Concurrent transcriptional activation of ppa and ppx genes by phosphate deprivation in the cyanobacterium Synechocystis sp. strain PCC 6803

The cyanobacterium Synechocystis sp. strain PCC 6803 possesses two genes, named ppa and ppx, which, respectively, encode proteins involved in the hydrolysis of inorganic phosphate polymers, namely, inorganic pyrophosphatase (PPA, EC 3.6.1.1), an essential enzyme that hydrolyzes pyrophosphate, and exopolyphosphatase (PPX, EC 3.6.1.11), a processive enzyme that releases the terminal orthophosphate group from linear polyphosphates. Northern blots showed that both single-copy genes are induced by long-term inorganic phosphate (P(i)) starvation, transcript levels being markedly increased (ca. 10- and 20-fold, respectively) relative to P(i)-sufficient cells. Concurrent increases of both PPA and PPX specific activities and protein levels by P(i) deprivation were also observed. On the other hand, a knockout mutant was obtained by insertional mutagenesis of ppx, but it could not be achieved with ppa, thus indicating that PPA function is essential for cell viability. Moreover, whereas the ppx mutant exhibited under P(i)-sufficient conditions lower growth rates than the wild-type and was certainly devoid of PPX activity, it showed a severe reduction of the PPA levels. These results are the first evidence on the involvement of both PPA and PPX in a possible intracellular P(i)-recycling enzymatic process activated under P(i)-starvation.