1H, 13C and 15N resonance assignment of phage T4 endoribonuclease RegB

RegB is involved in the control of the phage T4 life cycle. It inactivates the phage early mRNAs when their translation is no more required. We determined its structure and identified residues involved in substrate binding. For this, all backbone and 90% of side-chain resonance frequencies were assigned.     

High Dietary Magnesium Intake Is Associated with Low Insulin Resistance in the Newfoundland Population

Background

Magnesium plays a role in glucose and insulin homeostasis and evidence suggests that magnesium intake is associated with insulin resistance (IR). However, data is inconsistent and most studies have not adequately controlled for critical confounding factors.

Objective

The study investigated the association between magnesium intake and IR in normal-weight (NW), overweight (OW) and obese (OB) along with pre- and post- menopausal women.

Design

A total of 2295 subjects (590 men and 1705 women) were recruited from the CODING study. Dietary magnesium intake was computed from the Willett Food Frequency Questionnaire (FFQ). Adiposity (NW, OW and OB) was classified by body fat percentage (%BF) measured by Dual-energy X-ray absorptiometry according to the Bray criteria. Multiple regression analyses were used to test adiposity-specific associations of dietary magnesium intake on insulin resistance adjusting for caloric intake, physical activity, medication use and menopausal status.

Results

Subjects with the highest intakes of dietary magnesium had the lowest levels of circulating insulin, HOMA-IR, and HOMA-ß and subjects with the lowest intake of dietary magnesium had the highest levels of these measures, suggesting a dose effect. Multiple regression analysis revealed a strong inverse association between dietary magnesium with IR. In addition, adiposity and menopausal status were found to be critical factors revealing that the association between dietary magnesium and IR was stronger in OW and OB along with Pre-menopausal women.

Conclusion

The results of this study indicate that higher dietary magnesium intake is strongly associated with the attenuation of insulin resistance and is more beneficial for overweight and obese individuals in the general population and pre-menopausal women. Moreover, the inverse correlation between insulin resistance and dietary magnesium intake is stronger when adjusting for %BF than BMI.     

Structural and functional studies of RegB, a new member of a family of sequence-specific ribonucleases involved in mRNA inactivation on the ribosome

The RegB endoribonuclease participates in the bacteriophage T4 life cycle by favoring early messenger RNA breakdown. RegB specifically cleaves GGAG sequences found in intergenic regions, mainly in translation initiation sites. Its activity is very low but can be enhanced up to 100-fold by the ribosomal 30 S subunit or by ribosomal protein S1. RegB has no significant sequence homology to any known protein. Here we used NMR to solve the structure of RegB and map its interactions with two RNA substrates. We also generated a collection of mutants affected in RegB function. Our results show that, despite the absence of any sequence homology, RegB has structural similarities with two Escherichia coli ribonucleases involved in mRNA inactivation on translating ribosomes: YoeB and RelE. Although these ribonucleases have different catalytic sites, we propose that RegB is a new member of the RelE/YoeB structural and functional family of ribonucleases specialized in mRNA inactivation within the ribosome.     

The phage T4 restriction endoribonuclease RegB: a cyclizing enzyme that requires two histidines to be fully active

The regB gene, from the bacteriophage T4, codes for an endoribonuclease that controls the expression of a number of phage early genes. The RegB protein cleaves its mRNA substrates with an almost absolute specificity in the middle of the tertranucleotide GGAG, making it a unique well-defined restriction endoribonuclease. This striking protein has no homology to any known RNase and its catalytic mechanism has never been investigated. Here, we show, using ³¹P nuclear magnetic resonance (NMR), that RegB produces a cyclic 2′,3′-phosphodiester product. In order to determine the residues crucial for its activity, we prepared all the histidine-to- alanine point mutants of RegB. The activity of these mutants was characterized both in vivo and in vitro. In addition, their binding capability was quantified by surface plasmon resonance and their structural integrity was probed by ¹H/¹⁵N NMR correlation spectroscopy. The results obtained show that only the H48A and the H68A substitutions significantly reduce RegB activity without changing its ability to bind the substrate or affecting its overall structure. Altogether, our results define RegB as a new cyclizing RNase and present His48 and His68 as potent catalytic residues. The effect of the in vivo selected R52L mutation is also described and discussed.     

The relative priority of prekallikrein and factors XI/XIa assembly on cultured endothelial cells

Investigations determined the relative preference of prekallikrein (PK) or factor XI/XIa (FXI/FXIa) binding to endothelial cells (HUVECs). In microtiter plates, biotinylated high molecular weight kininogen (biotin-HK) or biotin-FXI binding to HUVEC monolayers or their matrix proteins, but not fibronectin-coated plastic microtiter plate wells, was specifically blocked by antibodies to each of the receptors of HK, uPAR, gC1qR, or cytokeratin 1. Fluorescein isothiocyanate (FITC)-PK specifically bound to HUVEC suspensions without added Zn2+, whereas FITC-FXI or -FXIa binding to HUVEC suspensions required 10 microM added Zn2+ to support specific binding. Plasma concentrations of FXI did not block FITC-PK binding to HUVECs in the absence or presence of 10 microM Zn2+. In the absence of HK, the level of FITC-FXI or -FXIa binding was half that seen in its presence. At physiologic concentrations, PK (450 nM) abolished FITC-FXI or -FXIa binding to HUVEC suspensions in the absence or presence of HK in the presence of 10 microM Zn2+. Released Zn2+ from 2-8 x 10(8) collagen-activated platelets/ml supported biotin-FXI binding to HUVEC monolayers, but platelet activation was not necessary to support biotin-PK binding to HUVECs. At physiologic concentrations, PK also abolished FXI binding to HUVECs in the presence of activated platelets, but FXI did not influence PK binding. PK in the presence or absence of HK preferentially bound to HUVECs over FXI or FXIa. Elevated Zn2+ concentrations are required for FXI but not PK binding, but the presence of physiologic concentrations of PK and HK also prevented FXI binding. PK preferential binding to endothelial cells contributes to their anticoagulant nature.     

Thyrsiferol Inhibits Mitochondrial Respiration and HIF-1 Activation

The cytotoxic marine red algal metabolite thyrsiferol (1) was found to inhibit hypoxia-induced hypoxia-inducible factor-1 (HIF-1) activation in T47D human breast tumor cells (66% inhibition at 3 μM). Compound 1 also suppressed hypoxic induction of HIF-1 target genes (VEGF, GLUT-1) at the mRNA level, and displayed tumor cell line-selective time-dependent inhibition of cell viability/proliferation. Mechanistic studies revealed that 1 selectively suppressed mitochondrial respiration at Complex I (IC(50) 3 μM). Thyrsiferol represents a prototypical, structurally unique electron transport chain inhibitor. The apparent rotenone-like activity may contribute to the observed cytotoxicity of 1 and play an important role in Laurencia chemical defense.     

The marine sponge metabolite mycothiazole: A novel prototype mitochondrial complex I inhibitor

A natural product chemistry-based approach was applied to discover small-molecule inhibitors of hypoxia-inducible factor-1 (HIF-1). A Petrosaspongia mycofijiensis marine sponge extract yielded mycothiazole (1), a solid tumor selective compound with no known mechanism for its cell line-dependent cytotoxic activity. Compound 1 inhibited hypoxic HIF-1 signaling in tumor cells (IC₅₀ 1 nM) that correlated with the suppression of hypoxia-stimulated tumor angiogenesis in vitro. However, 1 exhibited pronounced neurotoxicity in vitro. Mechanistic studies revealed that 1 selectively suppresses mitochondrial respiration at complex I (NADH-ubiquinone oxidoreductase). Unlike rotenone, MPP⁺, annonaceous acetogenins, piericidin A, and other complex I inhibitors, mycothiazole is a mixed polyketide/peptide-derived compound with a central thiazole moiety. The exquisite potency and structural novelty of 1 suggest that it may serve as a valuable molecular probe for mitochondrial biology and HIF-mediated hypoxic signaling.