Enhanced reactivity of amino-modified oligonucleotides by insertion of aromatic residue

Analysis of GTP addition in the reverse (3'-5') direction by human tRNAHis guanylyltransferase

Human tRNA^His guanylyltransferase (HsThg1) catalyzes the 3'-5' addition of guanosine triphosphate (GTP) to the 5'-end (-1 position) of tRNA^His, producing mature tRNA^His In human cells, cytoplasmic and mitochondrial tRNA^His have adenine (A) or cytidine (C), respectively, opposite to G_-1 Little attention has been paid to the structural requirements of incoming GTP in 3'-5' nucleotidyl addition by HsThg1. In this study, we evaluated the incorporation efficiencies of various GTP analogs by HsThg1 and compared the reaction mechanism with that of Candida albicans Thg1 (CaThg1). HsThg1 incorporated GTP opposite A or C in the template most efficiently. In contrast to CaThg1, HsThg1 could incorporate UTP opposite A, and guanosine diphosphate (GDP) opposite C. These results suggest that HsThg1 could transfer not only GTP, but also other NTPs, by forming Watson-Crick (WC) hydrogen bonds between the incoming NTP and the template base. On the basis of the molecular mechanism, HsThg1 succeeded in labeling the 5'-end of tRNA^His with biotinylated GTP. Structural analysis of HsThg1 was also performed in the presence of the mitochondrial tRNA^His Structural comparison of HsThg1 with other Thg1 family enzymes suggested that the structural diversity of the carboxy-terminal domain of the Thg1 enzymes might be involved in the formation of WC base-pairing between the incoming GTP and template base. These findings provide new insights into an unidentified biological function of HsThg1 and also into the applicability of HsThg1 to the 5'-terminal modification of RNAs.

The products from fermentation of wheat bran fiber by Auricularia polytricha strain and the effects of the products on rheological properties of dough sheet

Being classified within the Basidiomycota, Auricularia polytricha has been proved to degrade lignocellulose, a major component of wheat bran fiber. During the fermentation of lignocellulose by A. polytricha strain, a large number of intermediate products are produced, which affect the further degradation of lignocellulose. Therefore, it is essential to analyze the fermentation intermediates for study on the degradation mechanism of wheat bran fiber. In this study, the effectiveness of fermentation of wheat bran fiber by A. polytricha strain was confirmed via scanning electron microscopy. Additionally, the results of gas chromatography-mass spectrometry indicated that the A. polytricha strain could degrade wheat bran fiber and produce several aromatic compounds, and that the number of products obtained after 7 days of fermentation was significantly lower than that after 3 days of fermentation. It has also been demonstrated that diisooctyl phthalate and 9-octadecenamide belong to metabolites produced during the fermentation of wheat bran fiber, by culturing A. polytricha with wheat bran fiber and glucose as carbon source, respectively. Moreover, by conducting an ultraviolet wavelength scanning of the culture liquid containing vanillin fermented by A. polytricha, it has been indicated that the strain could degrade vanillin and further demonstrated that the strain has the ability to degrade wheat bran fiber. Furthermore, adding the products of wheat bran fiber fermented for 3 days by A. polytricha could improve the elasticity of the dough sheet.

Development of a 3'-amino linker with high conjugation activity and its application to conveniently cross-link blunt ends of a duplex

The 2-aminoethyl carbamate linker (ssH linker) exhibits high activity in modifying the 5'-termini of oligonucleotides; however, the ssH linker is not appropriate for 3'-terminal modification because it undergoes intramolecular trans-acylation under heat-aqueous ammonia conditions. We developed an N-(2-aminoethyl)carbamate linker (revH linker), in which the carbamate is oriented in the reverse direction relative to that in 2-aminoethyl carbamate. The revH linker was tolerant to heat-alkaline conditions and retained its high reactivity in conjugation with exogenous molecules. The 3'-revH linker was efficiently linked with the 5'-ssH linker at the termini of complementary double strands with a bifunctional molecule, producing a synthetic loop structure. An anti-microRNA oligonucleotide (AMO) was prepared from the chemical ligation of three-stranded 2'-O-methyl RNAs, and the AMO with two alkyl loops exhibited high inhibition activity toward miRNA function. The revH linker is not only useful for 3'-terminal modification of oligonucleotides but also expands the utility range in combination with the 5'-ssH linker.

Synthesis and application of highly reactive amino linkers for functional oligonucleotides

Oligonucleotides are functionalized by conjugation with a variety of molecules, and aliphatic amino linkers have been frequently used as a tether for their modifications. This unit describes the syntheses and applications of novel amino linkers having a carbamate structure. Two major chemical properties of the primary amine are induced by the neighboring effect of the carbamate group, which are found to be optimum in an aminoethyl carbamate structure. First, the hydrophobic monomethoxytrityl group can be rapidly removed from the aminoethyl carbamate under very mild acidic conditions, while the deprotection is not completed in standard aliphatic amines even under high acid concentration. This significant feature enables the convenient purification of amino-modified oligonucleotides by using the hydrophobic interaction of the monomethoxytrityl group with a reverse-phase resin. Second, the introduction of the carbamate linkage reduces the pK(a) value of the neighboring primary amine, resulting in an increase in the conjugation yields with various functional molecules, such as those having active esters. The novel amino linkers that have an aminoethyl carbamate linkage indicate potent activity and are applicable for the preparation of various functional oligonucleotides.

Nanomaterial-assisted signal enhancement of hybridization for DNA biosensors: a review

Detection of DNA sequences has received broad attention due to its potential applications in a variety of fields. As sensitivity of DNA biosensors is determined by signal variation of hybridization events, the signal enhancement is of great significance for improving the sensitivity in DNA detection, which still remains a great challenge. Nanomaterials, which possess some unique chemical and physical properties caused by nanoscale effects, provide a new opportunity for developing novel nanomaterial-based signal-enhancers for DNA biosensors. In this review, recent progress concerning this field, including some newly-developed signal enhancement approaches using quantum-dots, carbon nanotubes and their composites reported by our group and other researchers are comprehensively summarized. Reports on signal enhancement of DNA biosensors by non-nanomaterials, such as enzymes and polymer reagents, are also reviewed for comparison. Furthermore, the prospects for developing DNA biosensors using nanomaterials as signal-enhancers in future are also indicated.

Efficient synthesis of oligonucleotide conjugates on solid-support using an (aminoethoxycarbonyl)aminohexyl group for 5'-terminal modification

Solid-support conjugation at the 5'-terminal primary amine of oligonucleotides is a convenient and powerful method for introducing various functional groups. However, conventional aliphatic amines do not necessarily provide conjugates with sufficient yields. To improve the modification efficacy, we used the amino-linker (aminoethoxycarbonyl)aminohexyl group (ssH-linker), for solid-support conjugation. In the ssH-linker terminal modification, reactive free amino group could be easily presented onto a solid-support due to rapid removal of the amino-protecting group, and activated amino acids or cholesterol molecules could be covalently connected more efficiently than to typical 6-aminohexyl-linkers. Based on these results, the ssH-linker can be a useful terminal modification for the solid-support conjugation of functional molecules.

Novel amino linkers enabling efficient labeling and convenient purification of amino-modified oligonucleotides

We developed new amino linker reagents for an oligonucleotide (ONT) terminus. These reagents consist of an aminoethyl carbamate main linkage and a side-chain residue, which was a naphthylmethoxymethyl, methoxymethyl, or methyl group or a hydrogen atom. The primary amine was protected with a monomethoxytrityl (MMT) group. The chemical properties of ONTs containing these amino-modifications were investigated. The MMT group of these amino-modifications could be quite rapidly removed from the amine under very mild acidic conditions, which are not strong enough for the deprotection of a conventional aliphatic amine. This significant feature enabled the amino-modified ONTs to be conveniently purified with a reverse phase column. Furthermore, the amino-modifications efficiently reacted to active esters, as compared with other amino-modifications. We also found that the pK(a) values of the amino-modifications were lower than that of the aliphatic amine. All of the experimental results showed that these chemical properties are closely related to their structures. We report here the chemical properties and the availability of the new amino linker reagents.