Genetic and Physiological Characterization of Fructose-1,6-Bisphosphate Aldolase and Glyceraldehyde-3-Phosphate Dehydrogenase in the Crabtree-Negative Yeast Kluyveromyces lactis

The milk yeast Kluyveromyces lactis degrades glucose through glycolysis and the pentose phosphate pathway and follows a mainly respiratory metabolism. Here, we investigated the role of two reactions which are required for the final steps of glucose degradation from both pathways, as well as for gluconeogenesis, namely fructose-1,6-bisphosphate aldolase (FBA) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). In silico analyses identified one gene encoding the former (KlFBA1), and three genes encoding isoforms of the latter (KlTDH1, KlTDH2, KlGDP1). Phenotypic analyses were performed by deleting the genes from the haploid K. lactis genome. While Klfba1 deletions lacked detectable FBA activity, they still grew poorly on glucose. To investigate the in vivo importance of the GAPDH isoforms, different mutant combinations were analyzed for their growth behavior and enzymatic activity. KlTdh2 represented the major glycolytic GAPDH isoform, as its lack caused a slower growth on glucose. Cells lacking both KlTdh1 and KlTdh2 failed to grow on glucose but were still able to use ethanol as sole carbon sources, indicating that KlGdp1 is sufficient to promote gluconeogenesis. Life-cell fluorescence microscopy revealed that KlTdh2 accumulated in the nucleus upon exposure to oxidative stress, suggesting a moonlighting function of this isoform in the regulation of gene expression. Heterologous complementation of the Klfba1 deletion by the human ALDOA gene renders K. lactis a promising host for heterologous expression of human disease alleles and/or a screening system for specific drugs.

Effects of the Chloroplast Fructose-1,6-Bisphosphate Aldolase Gene on Growth and Low-Temperature Tolerance of Tomato

Tomato (Solanum lycopersicum) is one of the most important greenhouse vegetables, with a large cultivated area across the world. However, in northern China, tomato plants often suffer from low-temperature stress in solar greenhouse cultivation, which affects plant growth and development and results in economic losses. We previously found that a chloroplast aldolase gene in tomato, SlFBA4, plays an important role in the Calvin-Benson cycle (CBC), and its expression level and activity can be significantly altered when subjected to low-temperature stress. To further study the function of SlFBA4 in the photosynthesis and chilling tolerance of tomato, we obtained transgenic tomato plants by the over-expression and RNA interference (RNAi) of SlFBA4. The over-expression of SlFBA4 led to higher fructose-1,6-bisphosphate aldolase activity, net photosynthetic rate (Pn) and activity of other enzymes in the CBC than wild type. Opposite results were observed in the RNAi lines. Moreover, an increase in thousand-seed weight, plant height, stem diameter and germination rate in optimal and sub-optimal temperatures was observed in the over-expression lines, while opposite effects were observed in the RNAi lines. Furthermore, over-expression of SlFBA4 increased Pn and enzyme activity and decreased malonaldehyde (MDA) content under chilling conditions. On the other hand, Pn and MDA content were more severely influenced by chilling stress in the RNAi lines. These results indicate that SlFBA4 plays an important role in tomato growth and tolerance to chilling stress.

Comparative proteomic analysis of Fusarium oxysporum f. sp. cubense strains (Foc R1 and Foc TR4) provides better insights into mechanisms of their virulence, habitat adaptation and pathogenesis

Fusarium oxysporum f. sp. cubense (Foc), a devastative soil-borne fungal pathogen causing vascular wilt (i.e. Panama disease) which leads to severe crop losses in most of the banana-growing regions of the world. As there is no single source of effective management practices available so far, understand the pathogenicity of the organism may help in designing effective control measures through molecular approaches. The study aims to compare the proteome of the two pathogenic Foc virulent strains, Race 1 (Foc R1) and tropical race 4 (Foc TR4) that are capable of infecting the Cavendish group of bananas using 2-dimensional (2-D) gel electrophoresis, MALDI-TOF/MS and MS/MS analysis. The results of the study revealed that the proteins, peroxiredoxins, NAD-aldehyde dehydrogenase (NAD-ALDH), MAPK protein, pH-response regulator protein palA/rim-20 and isotrichodermin C15 hydroxylase have shared homology with the fungal proteins, which regulate the osmotic stress response, signal transduction, root colonization and toxin biosynthesis. These are the important functions for the pathogen survival in an unfavourable environment, and successful establishment and infection of the banana host. The present study also identified several putative pathogenicity related proteins in both Foc R1 and Foc TR4. Specifically, certain Foc TR4 specific putative pathogenicity related proteins, phytotoxins biosynthesis gene, fructose 1,6-bisphosphate aldolase class II, Synembryn-like proteins found to contribute strong virulence. Overexpression or knockout of the elective genes could help in devising better control measures for the devastative pathogens in the future. To the best of our knowledge, this is the first report on the proteomics of Foc R1 and Foc TR4 strains of Indian origin that infect Cavendish bananas.

Crystal structure of chloroplast fructose-1,6-bisphosphate aldolase from the green alga Chlamydomonas reinhardtii

The Calvin-Benson cycle fixes carbon dioxide into organic triosephosphates through the collective action of eleven conserved enzymes. Regeneration of ribulose-1,5-bisphosphate, the substrate of Rubisco-mediated carboxylation, requires two lyase reactions catalyzed by fructose-1,6-bisphosphate aldolase (FBA). While cytoplasmic FBA has been extensively studied in non-photosynthetic organisms, functional and structural details are limited for chloroplast FBA encoded by oxygenic phototrophs . Here we determined the crystal structure of plastidial FBA from the unicellular green alga Chlamydomonas reinhardtii (Cr). We confirm that CrFBA folds as a TIM barrel, describe its catalytic pocket and homo-tetrameric state. Multiple sequence profiling classified the photosynthetic paralogs of FBA in a distinct group from non-photosynthetic paralogs. We mapped the sites of thiol- and phospho-based post-translational modifications known from photosynthetic organisms and predict their effects on enzyme catalysis.

Glycolytic flux-signaling controls mouse embryo mesoderm development

How cellular metabolic state impacts cellular programs is a fundamental, unresolved question. Here we investigated how glycolytic flux impacts embryonic development, using presomitic mesoderm (PSM) patterning as the experimental model. First, we identified fructose 1,6-bisphosphate (FBP) as an in vivo sentinel metabolite that mirrors glycolytic flux within PSM cells of post-implantation mouse embryos. We found that medium-supplementation with FBP, but not with other glycolytic metabolites, such as fructose 6-phosphate and 3-phosphoglycerate, impaired mesoderm segmentation. To genetically manipulate glycolytic flux and FBP levels, we generated a mouse model enabling the conditional overexpression of dominant active, cytoplasmic Pfkfb3 (cytoPfkfb3). Overexpression of cytoPfkfb3 indeed led to increased glycolytic flux/FBP levels and caused an impairment of mesoderm segmentation, paralleled by the downregulation of Wnt-signaling, reminiscent of the effects seen upon FBP-supplementation. To probe for mechanisms underlying glycolytic flux-signaling, we performed subcellular proteome analysis and revealed that cytoPfkfb3 overexpression altered subcellular localization of certain proteins, including glycolytic enzymes, in PSM cells. Specifically, we revealed that FBP supplementation caused depletion of Pfkl and Aldoa from the nuclear-soluble fraction. Combined, we propose that FBP functions as a flux-signaling metabolite connecting glycolysis and PSM patterning, potentially through modulating subcellular protein localization.

Characterization of Fructose-1,6-Bisphosphate Aldolase 1 of Echinococcus multilocularis

Glycolysis is one of the important ways by which Echinococcus multilocularis acquires energy. Fructose-1, 6-bisphosphate aldolase (FBA) plays an important role in this process, but it is not fully characterized in E. multilocularis yet. The results of genome-wide analysis showed that the Echinococcus species contained four fba genes (FBA1-4), all of which had the domain of FBA I and multiple conserved active sites. EmFBA1 was mainly located in the germinal layer and the posterior of the protoscolex. The enzyme activity of EmFBA1 was 67.42 U/mg with Km and Vmax of 1.75 mM and 0.5 mmol/min, respectively. EmFBA1 was only susceptible to Fe3+ but not to the other four ions (Na+, Ca2+, K+, Mg2+), and its enzyme activity was remarkably lost in the presence of 0.5 mM Fe3+. The current study reveals the biochemical characters of EmFBA1 and is informative for further investigation of its role in the glycolysis in E. multilocularis.

Coxiella burnetii inhibits host immunity by a protein phosphatase adapted from glycolysis

Coxiella burnetii is a bacterial pathogen that replicates within host cells by establishing a membrane-bound niche called the Coxiella-containing vacuole. Biogenesis of this compartment requires effectors of its Dot/Icm type IV secretion system. A large cohort of such effectors has been identified, but the function of most of them remain elusive. Here, by a cell-based functional screening, we identified the effector Cbu0513 (designated as CinF) as an inhibitor of NF-κB signaling. CinF is highly similar to a fructose-1,6-bisphosphate (FBP) aldolase/phosphatase present in diverse bacteria. Further study reveals that unlike its ortholog from Sulfolobus tokodaii, CinF does not exhibit FBP phosphatase activity. Instead, it functions as a protein phosphatase that specifically dephosphorylates and stabilizes IκBα. The IκBα phosphatase activity is essential for the role of CinF in C. burnetii virulence. Our results establish that C. burnetii utilizes a protein adapted from sugar metabolism to subvert host immunity.

Glucose-1,6-bisphosphate, a key metabolic regulator, is synthesized by a distinct family of α-phosphohexomutases widely distributed in prokaryotes

The reactions of α-D-phosphohexomutases (αPHM) are ubiquitous, key to primary metabolism and essential for several processes in all domains of life. The functionality of these enzymes relies on an initial auto-phosphorylation step which requires the presence of α-D-glucose-1,6-bisphosphate (Glc-1,6-BP). While well investigated in vertebrates, the origin of this activator compound in bacteria is unknown. Here we show that the Slr1334 protein from the unicellular cyanobacterium Synechocysitis sp. PCC 6803 is a Glc-1,6-BP-synthase. Biochemical analysis revealed that Slr1334 efficiently converts fructose-1,6-bisphosphate and α-D-glucose-1-phosphate/α-D-glucose-6-phosphate into Glc-1,6-BP and also catalyzes the reverse reaction. Phylogenetic analysis revealed that the slr1334 product belongs to a primordial subfamily of αPHMs that is present especially in deeply branching bacteria and also includes human commensals and pathogens. Interestingly, the homologue of Slr1334 in the human gut bacterium Bacteroides salyersiae catalyzes the same reaction, suggesting a conserved and essential role for the members of this αPHM subfamily.

Multispecies populations of methanotrophic Methyloprofundus and cultivation of a likely dominant species from the Iheya North deep-sea hydrothermal field

The Methyloprofundus clade is represented by uncultivated methanotrophic bacterial endosymbionts of deep-sea bathymodiolin mussels, but only a single free-living species has been cultivated to date. This study reveals the existence of free-living Methyloprofundus variants in the Iheya North deep-sea hydrothermal field in the mid-Okinawa Trough. A clade-targeted amplicon analysis of the particulate methane monooxygenase gene ( pmoA ) detected 647 amplicon sequence variants (ASVs) of the Methyloprofundus clade in microbial communities newly formed in in situ colonization systems. Such systems were deployed at colonies of bathymodiolin mussels and a galatheoid crab. These ASVs were classified into 161 species-like groups. The proportion of the species-like groups representing endosymbionts of mussels was unexpectedly low. A methanotrophic bacterium designated as INp10, a likely dominant species in the Methyloprofundus population in this field, was enriched in biofilm formed in a methane-fed cultivation system operated at 10°C. Genomic characterization with the gene transcription dataset of INp10 from biofilm suggested traits advantageous to niche competition in environments, such as mobility, chemotaxis, biofilm formation, offensive and defensive systems, and hypoxia tolerance. The notable metabolic traits INp10 shares with some Methyloprofundus members are the use of lanthanide-dependent XoxF as the sole methanol dehydrogenase due to the absence of the canonical MxaFI, the glycolytic pathway using fructose-6-phosphate aldolase instead of fructose-1,6-bisphosphate aldolase, and the potential to perform partial denitrification from nitrate under oxygen-limited conditions. These findings help better understand ecological strategies of this possibly widespread marine-specific methanotrophic clade. Importance The Iheya North deep-sea hydrothermal field in the mid-Okinawa Trough is characterized by abundant methane derived from organic-rich sediments and diverse chemosynthetic animal species, including those harboring methanotrophic bacterial symbionts such as bathymodiolin mussels Bathymodiolus japonicus and “ Bathymodiolus ” platifrons and a galatheoid crab Shinkaia crosnieri . Symbiotic methanotrophs have attracted significant attention, yet free-living methanotrophs in this environment have not been studied in detail. We focused on the free-living Methyloprofundus spp. that thrive in this hydrothermal field and identified an unexpectedly large number of species-like groups in this clade. Moreover, we enriched and characterized a methanotroph whose genome sequence indicated it corresponds to a new species in the genus Methyloprofundus . This species might be a dominant member of the indigenous Methyloprofundus population. New information on free-living Methyloprofundus spp. suggests that the hydrothermal field is a promising locale to investigate the adaptive capacity and associated genetic diversity of Methyloprofundus .