Inhibitory effect of methylated derivatives of guanylic acid for protein synthesis with reference to the functional structure of the 5'-'cap' in viral messenger RNA

Assessment of the effect of methyl-triclosan and its mixture with triclosan on developing zebrafish (Danio rerio) embryos using mass spectrometry-based metabolomics

Methyl-triclosan (MTCS), as a biodegradation product from antibacterial triclosan (TCS), has been detected in water catchments, and it has also been verified to accumulate in biota due to its hydrophobicity. There is a lack, however, of toxicity studies on MTCS and its effects on organisms in conjunction with TCS. In this study, exposure experiments were conducted to assess the toxicity to embryonic zebrafish of selected concentrations of MTCS (from 1 ng/L to 400 μg/L) and MTCS/TCS mixtures (from 1 μg/L TCS and 100 ng/L MTCS to 300 μg/L TCS and 30 μg/L MTCS). Specimens were extracted using acetonitrile: isopropanol: water (3:3:2; v/v/v) and then analyzed using Gas chromatography-mass spectrometry (GC-MS) to identify the metabolites based on the Fiehn library database. The results showed that MTCS exposure led to the alterations of the metabolomes of the zebrafish embryos, including level changes of l-valine, d-mannose, d-glucose, and other metabolites. Multivariate analysis (PCA, PLS-DA, sPLS-DA) and univariate analysis (one-way ANOVA) indicated differences between the control and exposure groups of the metabolites, indicating that biological pathways, such as amino acid synthesis, pentose phosphate pathway (PPP), starch and sucrose metabolism were influenced. Moreover, when the embryos were exposed to a mix of TCS and MTCS, TCS dominated the mixture's effect on biological pathways because the concentration ratio within the mixture, which mimics environmental ratio of 10 TCS : 1 MTCS, leads to high bioavailability of TCS.

Quantitative assessment of mRNA cap analogues as inhibitors of in vitro translation

Fifty-eight analogues of the 5'-terminal 7-methylguanosine-containing cap of eukaryotic messenger RNA were synthesized and tested for their ability to inhibit in vitro protein synthesis. A new algorithm was developed for extracting KI, the dissociation constant for the cap analogue.eIF4E complex, from protein synthesis data. The results indicated that addition of a methyl group to the N2 of guanine produced more inhibitory compounds, but addition of a second methyl group to N2 decreased the level of inhibition dramatically. Aryl substitution at N7 improved the efficacy of guanine nucleoside monophosphate analogues. Substitution of the aromatic ring at the para position with methyl or NO2 groups abolished this effect, but substitution with Cl or F enhanced it. By contrast, aryl substitution at N7 in nucleoside di- or triphosphate analogues produced only minor effects, both positive and negative. By far the strongest determinants of inhibitory activity for cap analogues were phosphate residues. The beneficial effect of more phosphate residues was related more to anionic charge than to the number of phosphate groups per se. The second nucleotide residue in analogues of the form m7GpppN affected inhibitory activity in the order G > C > U > A, but there was no effect of 2'-O-modification. Opening the first ribose ring of m7GpppG analogues dramatically decreased activity, but alterations at the 2'-position of this ribose had no effect. Non-nucleotide-based cap analogues containing benzimidazole derivatives were inhibitory, though less so than those containing 7-methylguanine.

Inhibition of eukaryotic translation by nucleoside 5'-monophosphate analogues of mRNA 5'-cap: changes in N7 substituent affect analogue activity

Nucleotide cap analogues of 7-methylguanosine 5'-monophosphate (m7GMP) were synthesized in which the 7-methyl moiety was replaced with 7-ethyl (e7), 7-propyl (p7), 7-isopropyl (ip7), 7-butyl (b7), 7-isobutyl (ib7), 7-cyclopentyl (cp7), 7-(carboxymethyl) (cm7), 7-benzyl (bn7), 7-(2-phenylethyl) [7-(2-PhEt)], and 7-(1-phenylethyl) [7-(1-PhEt)]. These derivatives were assayed as competitive inhibitors of capped mRNA translation in reticulocyte lysate. We observed that N7 alkyl and alicyclic substituents larger than ethyl significantly decreased the inhibitory activity of these cap analogues presumably by decreasing their affinity for cap binding proteins, which participate in the initiation of translation. This result defined a maximum size for this class of N7 substituents in the nucleotide binding domain of cap binding proteins. Like m7GMP, the N7-substituted GMP derivatives synthesized in this study were found to be predominantly in the anti conformation as determined by proton NMR analyses. However, bn7GMP and 7-(2-PhEt)GMP, which have aromatic N7 substituents, were more effective than m7GMP as competitive inhibitors of translation. The increased affinity of bn7GMP for cap binding proteins was further examined by synthesis of beta-globin mRNA containing 5'-bn7G, 5'-m7G, or 5'-e7G cap structures. These modified mRNAs were tested as translation templates. Messenger RNA capped with bn7G was observed to increase the translation activity of the template 1.8-fold relative to that of its m7G-capped mRNA counterpart. By contrast, e7G-capped mRNA was 25% less active than m7G-capped mRNA.2+V photo-cross-linking of m7G-capped mRNA to cap binding proteins

Beta-globin mRNAs capped with m7G, m2.7(2)G or m2.2.7(3)G differ in intrinsic translation efficiency

We examined the intramolecular effect of altered cap structures on translation efficiency of artificial beta-globin mRNAs. For these studies, synthetic dinucleotides of the form X(5')ppp(5')G [X = 7-methyl guanosine (m7G), 2,7-dimethyl guanosine (m2(2,7)G) or 2,2,7-trimethyl guanosine (m3(2,2,7)G)], were transcriptionally incorporated into mRNAs, containing rabbit beta-globin coding sequences, using T7 RNA polymerase and a beta-globin cDNA template. These synthetic mRNAs were assayed in reticulocyte lysate for activity relative to m7G-capped mRNA. m2(2,7)G-Capped mRNA was found to be 1.5-fold more active than m7G-capped mRNA. Messenger RNA capped with m3(2,2,7)G was less active with activity of 0.24 relative to its m7G-capped counterpart (activity = 1.0). These data suggest that m7G-capped mRNAs become more active as translation templates after addition of a single N2 methyl moiety, which is especially pertinent to gene expression in togaviridae. The latter are observed to synthesize m2(2,7)G and m3(2,2,7)G-capped mRNAs in addition to m7G-capped templates during the course of infection in animal cells.

Relationship between structure of the 5' noncoding region of viral mRNA and efficiency in the initiation step of protein synthesis in a eukaryotic system

To determine whether the rate of protein synthesis is controlled by the structure of mRNA near its 5' terminus, protein-synthesizing ability, especially in its initial stage, was compared among RNAs of plant viruses. Those viruses used here contain several definite pieces of single-stranded RNA. Each of these RNAs acts as a messenger. Cucumber mosaic virus (CMV) RNA 5 synthesizes a small amount of a protein, Mr 7000, in an in vitro protein-synthesizing system from wheat germ or reticulocyte. Brome mosaic virus (BMV) RNA 4 synthesizes a large amount of a coat protein under the same conditions. Both RNAs have the same 5'-cap structure and a short noncoding region (10 nucleotides in CMV RNA 5 and 9 in BMV RNA 4) between the 5' terminus and the initiation codon AUG. A sequence complementary to the 3' terminal of 18S ribosomal RNA is contained in BMV RNA 4 but is not apparent in CMV RNA 5. Formation of the initiation complex for protein synthesis by the 5'-terminal-labeled mRNA of cytoplasmic polyhedrosis virus was inhibited by the addition of unlabeled BMV RNA 4 whereas it was only slightly inhibited by unlabeled CMV RNA 5. BMV RNA 4, which has a sequence complementary to rRNA, can form the initiation complex more easily than CMV RNA5. It is concluded that an apparent complementary sequence in the 3' terminal of 18S rRNA in the 5' noncoding region of eukaryotic mRNA and the 5'-cap structure enhance the rate of initiation complex formation in protein synthesis.