The tetrapyrroles haem, bacteriochlorophyll and cobalamin (B12 ) exhibit a complex interrelationship regarding their synthesis. In this study, we demonstrate that AerR functions as an antirepressor of the tetrapyrrole regulator CrtJ. We show that purified AerR contains B12 that is bound to a conserved histidine (His145) in AerR. The interaction of AerR to CrtJ was further demonstrated in vitro by pull down experiments using AerR as bait and quantified using microscale thermophoresis. DNase I DNA footprint assays show that AerR containing B12 inhibits CrtJ binding to the bchC promoter. We further show that bchC expression is greatly repressed in a B12 auxotroph of Rhodobacter capsulatus and that B12 regulation of gene expression is mediated by AerR's ability to function as an antirepressor of CrtJ. This study thus provides a mechanism for how the essential tetrapyrrole, cobalamin controls the synthesis of bacteriochlorophyll, an essential component of the photosystem.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
The dramatic growth that occurs during Drosophila larval development requires rapid conversion of nutrients into biomass. Many larval tissues respond to these biosynthetic demands by increasing carbohydrate metabolism and lactate dehydrogenase (dLDH) activity. The resulting metabolic program is ideally suited to synthesize macromolecules and mimics the manner by which cancer cells rely on aerobic glycolysis. To explore the potential role of Drosophila dLDH in promoting biosynthesis, we examined how dLdh mutations influence larval development. Our studies unexpectantly found that dLdh mutants grow at a normal rate, indicating that dLDH is dispensable for larval biomass production. However, subsequent metabolomic analyses suggested that dLdh mutants compensate for the inability to produce lactate by generating excess glycerol-3-phosphate (G3P), the production of which also influences larval redox balance. Consistent with this possibility, larvae lacking both dLDH and G3P dehydrogenase (GPDH1) exhibit growth defects, synthetic lethality, and decreased glycolytic flux. Considering that human cells also generate G3P upon Lactate Dehydrogenase A (LDHA) inhibition, our findings hint at a conserved mechanism in which the coordinate regulation of lactate and G3P synthesis imparts metabolic robustness upon growing animal tissues.
Necrotizing enterocolitis (NEC) is a devastating disease of the neonatal gastrointestinal tract. Volatile organic compounds (VOCs), odoriferous compounds released as a byproduct of bacterial metabolism, can be used as a proxy for gut health. We hypothesized that patients with NEC would have different microbial profiles and elicit different VOC signatures as assessed by gas chromatography/mass spectrometry (GC/MS) or an electronic nose compared to controls. Furthermore, we hypothesized that the temperature of sample storage and the length of time in storage would impact the VOC signatures. Forty-five human stool samples were obtained from Neonatal Intensive Care Units. They were stored at -80 °C as part of the Necrotizing Enterocolitis Biorepository. The microbiome composition was determined by 16S-rRNA gene sequencing and VOC profiles were obtained with GC-MS and by analysis with the Cyranose 320 electronic nose. In separate experiments, fresh stool samples were collected from three different strains of mice. Samples were stored for different times and different temperatures, and VOC signals were compared. A p-value less than 0.05 was considered significant. 16S-rRNA sequencing found a difference in the microbiome composition (p = 0.025) between human NEC and control samples. There was also a difference observed between NEC and control samples identified by GC-MS (p = 0.001). However, there were no differences in VOC smellprints between NEC and controls when analyzed with an electronic nose. When mouse specimens were analyzed, principal component values changed significantly over time and with different storage temperatures. NEC is associated with a different gut microbiome and the VOC profile compared to age-matched controls. However, this difference was not appreciated when biobanked stool samples were compared via an electronic nose. Older samples may experience VOC decay, or the electronic nose may not be sensitive enough to detect NEC in stool samples. Further studies on fresh human stool samples are needed, but the findings herein may limit the use of electronic noses as diagnostic tools for NEC.
Structural rigidity is verified as a pre-organizational factor that acts together with the macrocyclic effect such that synthesis helps in paying the cost of bringing together electropositive CH donors ready for H-bonding with chloride.
Abstract Triazolophanes are used as the venue to compete an aliphatic propylene CH hydrogen‐bond donor against an aromatic phenylene one. Longer aliphatic CH ⋅⋅⋅ Cl − hydrogen bonds were calculated from the location of the chloride within the propylene‐based triazolophane. The gas‐phase energetics of chloride binding (Δ G bind , Δ H bind , Δ S bind ) and the configurational entropy (Δ S config ) were computed by taking all low‐energy conformations into account. Comparison between the phenylene‐ and propylene‐based triazolophanes shows the computed gas‐phase free energy of binding decreased from Δ G bind =−194 to −182 kJ mol −1 , respectively, with a modest enthalpy–entropy compensation. These differences were investigated experimentally. An 1 H NMR spectroscopy study on the structure of the propylene triazolophane’s 1:1 chloride complex is consistent with a weaker propylene CH hydrogen bond. To quantify the affinity differences between the two triazolophanes in dichloromethane, it was critical to obtain an accurate binding model. Four equilibria were identified. In addition to 1:1 complexation and 2:1 sandwich formation, ion pairing of the tetrabutylammonium chloride salt (TBA + ⋅ Cl − ) and cation pairing of TBA + with the 1:1 triazolophane–chloride complex were observed and quantified. Each complex was independently verified by ESI‐MS or diffusion NMR spectroscopy. With ion pairing deconvoluted from the chloride–receptor binding, equilibrium constants were determined by using 1 H NMR (500 μ M ) and UV/Vis (50 μ M ) spectroscopy titrations. The stabilities of the 1:1 complexes for the phenylene and propylene triazolophanes did not differ within experimental error, Δ G =(−38±2) and (−39±1) kJ mol −1 , respectively, as verified by an NMR spectroscopy competition experiment. Thus, the aliphatic CH donor only revealed its weaker character when competing with aromatic CH donors within the propylene‐based triazolophane.
