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ABSTRACT: We have previously reported the in vitro selection of a ribozyme that catalyzes an aldol reaction between a levulinic amide aldol donor and a benzaldehyde substrate. The selection scheme involved the priming of the RNA library with a levulinic amide aldol donor group that was introduced via transcription priming in the presence of a modified guanosine mononucleotide derivative. Here we provide a detailed description of the synthesis of the ribozyme substrates and the substrate oligonucleotides used for its isolation and characterization. The aldol donor group was attached to the phosphate moiety of guanosine monophosphate via a photocleavable linker molecule. This initiator nucleotide was efficiently incorporated into RNA molecules of differing sizes and composition by transcription priming with T7 RNA polymerase. With this method modified RNA oligonucleotides as small as a 6-mer sequence can be generated. A temperature profile of the intermolecular reaction indicates that the modified RNA hexamer binds the ribozyme largely by Watson-Crick pairing and only to a minor extent via the non-RNA moiety, whereas the ribozyme appears to have evolved a specific binding site for the aldehyde substrate.
The Journal of Organic Chemistry 08/2008; 73(13):5069-77. · 4.45 Impact Factor
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ABSTRACT: In vitro selection can be used to generate functional nucleic acids such as aptamers and ribozymes that can recognize a variety of molecules with high affinity and specificity. Most often these recognition events are associated with structural alterations that can be converted into detectable signals. Several signaling aptamers and ribozymes constructed by both design and selection have been successfully utilized as sensitive detection reagents. Here we summarize the development of different types of signaling nucleic acids, and approaches that have been implemented in the screening format.
Combinatorial Chemistry & High Throughput Screening 10/2007; 10(8):698-705. · 1.78 Impact Factor
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ABSTRACT: G proteins are an important class of regulatory switches in all living systems. They are activated by guanine nucleotide exchange factors (GEFs), which facilitate the exchange of GDP for GTP. This activity makes GEFs attractive targets for modulating disease-relevant G-protein-controlled signalling networks. GEF inhibitors are therefore of interest as tools for elucidating the function of these proteins and for therapeutic intervention; however, only one small molecule GEF inhibitor, brefeldin A (BFA), is currently available. Here we used an aptamer displacement screen to identify SecinH3, a small molecule antagonist of cytohesins. The cytohesins are a class of BFA-resistant small GEFs for ADP-ribosylation factors (ARFs), which regulate cytoskeletal organization, integrin activation or integrin signalling. The application of SecinH3 in human liver cells showed that insulin-receptor-complex-associated cytohesins are required for insulin signalling. SecinH3-treated mice show increased expression of gluconeogenic genes, reduced expression of glycolytic, fatty acid and ketone body metabolism genes in the liver, reduced liver glycogen stores, and a compensatory increase in plasma insulin. Thus, cytohesin inhibition results in hepatic insulin resistance. Because insulin resistance is among the earliest pathological changes in type 2 diabetes, our results show the potential of chemical biology for dissecting the molecular pathogenesis of this disease.
Nature 01/2007; 444(7121):941-4. · 36.28 Impact Factor
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ABSTRACT: Directed in vitro evolution can create RNA catalysts for a variety of organic reactions, supporting the "RNA world" hypothesis, which proposes that metabolic transformations in early life were catalyzed by RNA molecules rather than proteins. Among the most fundamental carbon-carbon bond-forming reactions in nature is the aldol reaction, mainly catalyzed by aldolases that utilize either an enamine mechanism (class I) or a Zn(2+) cofactor (class II). We report on isolation of a Zn(2+)-dependent ribozyme that catalyzes an aldol reaction at its own modified 5' end with a 4300-fold rate enhancement over the uncatalyzed background reaction. The ribozyme can also act as an intermolecular catalyst that transfers a biotinylated benzaldehyde derivative to the aldol donor substrate, coupled to an external hexameric RNA oligonucleotide, supporting the existence of RNA-originated biosynthetic pathways for metabolic sugar precursors and other biomolecules.
Chemistry & Biology 09/2005; 12(8):941-50. · 5.83 Impact Factor
