The mycobacterial guaB1 gene encodes a guanosine 5'-monophosphate reductase with a cystathione-β-synthase domain

Purine metabolism plays a pivotal role in bacterial life cycle, however, regulation of the de novo and purine salvage pathways have not been extensively detailed in mycobacteria. By gene knockout, biochemical and structural analyses, we identified Mycobacterium smegmatis (Msm) and Mycobacterium tuberculosis (Mtb) guaB1 gene product as a novel type of guanosine 5'-monophosphate reductase (GMPR), which recycles guanosine monophosphate to inosine monophosphate within the purine salvage pathway and contains cystathione β-synthase (CBS) domains with atypical orientation in the octamer. CBS domains share a much larger interacting area with a conserved catalytic domain in comparison with the only known CBS containing protozoan GMPR and closely related inosine monophosphate dehydrogenase structures. Our results revealed essential effect of pH on allosteric regulation of Msm GMPR activity and oligomerization with adenine and guanosine nucleotides binding to CBS domains.Bioinformatic analysis indicated the presence of GMPRs containing CBS domains across the entire Actinobacteria phylum.

Effect of hypoxia on purine metabolism of human skeletal muscle cells

Mammals experience some degree of hypoxia during their lifetime. In response to hypoxic challenge, mammalian cells orchestrate specific responses at transcriptional and posttranslational level which lead to changes in the purine metabolites in order to cope with threatening conditions. The aim of this study was to evaluate the response of the enzymes involved in the purine metabolism of human muscle cells to hypoxic conditions. Muscle cells in culture were exposed to hypoxia and the enzymatic activity of inosine monophosphate dehydrogenase (IMPDH), xanthine oxidase (XO), purine nucleoside phosphorylase (PNP) and hypoxanthine guanine phosphoribosyl transferase (HGPRT) as well as their transcript expression were quantified under normoxic and hypoxic conditions. Purine metabolite (hypoxanthine (HX), xanthine (X), uric acid (UA), inosine monophosphate (IMP), inosine, nicotinamide adenine dinucleotide (NAD+), adenosine, adenosine monophosphate (AMP), adenosine diphosphate (ADP), adenosine triphosphate (ATP), guanosine diphosphate (GDP) and guanosine triphosphate (GTP)) concentrations were also quantified. Significant reduction of IMPDH activity and HX and IMP concentrations (p < 0.05) were observed after hypoxia, suggesting a decrease of de novo synthesis of purines. After hypoxia a global reduction of transcripts was observed, suggesting a reduction of the metabolic machinery of purine metabolism to new steady states that balance ATP demand and ATP supply pathways.

Gm14230 controls Tbc1d24 cytoophidia and neuronal cellular juvenescence

It is not fully understood how enzymes are regulated in the tiny reaction field of a cell. Several enzymatic proteins form cytoophidia, a cellular macrostructure to titrate enzymatic activities. Here, we show that the epileptic encephalopathy-associated protein Tbc1d24 forms cytoophidia in neuronal cells both in vitro and in vivo. The Tbc1d24 cytoophidia are distinct from previously reported cytoophidia consisting of inosine monophosphate dehydrogenase (Impdh) or cytidine-5’-triphosphate synthase (Ctps). Tbc1d24 cytoophidia is induced by loss of cellular juvenescence caused by depletion of Gm14230, a juvenility-associated lncRNA (JALNC) and zeocin treatment. Cytoophidia formation is associated with impaired enzymatic activity of Tbc1d24. Thus, our findings reveal the property of Tbc1d24 to form cytoophidia to maintain neuronal cellular juvenescence.

Evaluation of Dietary Soluble Extract Hydrolysates with or without Supplementation of Inosine Monophosphate Based on Growth, Hematology, Non-Specific Immune Responses and Disease Resistance in Juvenile Nile Tilapia Oreochromis niloticus

We performed an 8-week feeding trial to evaluate dietary soluble extract hydrolysates from fishery by-products, such as shrimp soluble extract (SSE) with or without inosine monophosphate (IMP), tilapia soluble extract (TSE) and squid soluble extract (SQSE), in juvenile Nile tilapia. A diet without feed additives was used as the control diet (CON); and five other experimental diets were formulated with 2% soluble extracts consisting of 100% SSE, 98% SSE + 2% IMP (SSEP2), 96% SSE + 4% IMP (SSEP4), 100% SQSE and 100% TSE. The diets were fed to 4.9 ± 0.07 g (mean ± SD) juvenile Nile tilapia in triplicate groups. The weight gain and specific growth rates of fish fed the SSE, SSEP2 and SSEP4 diets were significantly higher than those of fish fed the CON and SQSE diets. The superoxide dismutase activity levels of fish fed the SSE and SSEP4 diets were significantly higher than those of fish fed the CON, SSEP2, SQSE and TSE diets. Myeloperoxidase activity levels of fish fed the SSE and SSEP4 diets were significantly higher than those of fish fed the CON, SSEP2 and SQSE diets. Lysozyme activity levels of fish fed the SSEP4 and SQSE diets were significantly higher than those of fish fed the SSE and SSEP2 diets. Feed efficiency, protein efficiency ratio, survival rate, whole body proximate composition and hematological parameters were not significantly different among the groups. After ten days of challenge = against Aeromonas hydrophila, the cumulative survival rate of fish fed the SSE diet was significantly higher than those of fish fed the CON, SQSE and TSE diets. In conclusion, dietary shrimp soluble extract could improve the growth performance, non-specific immune responses and disease resistance in juvenile Nile tilapia, and inosine monophosphate did not add further benefits to this ingredient.