RESUMO
5-Bromouracil ((Br)U) was incorporated into three types of synthetic RNA and the products of the photoirradiated (Br)U-containing RNAs were investigated using HPLC and MS analysis. The photoirradiation of r(GCA(Br)UGC)(2) and r(CGAA(Br)UUGC)/r(GCAAUUCG) in A-form RNA produced the corresponding 2'-keto adenosine ((keto)A) product at the 5'-neighboring nucleotide, such as r(GC(keto)AUGC) and r(CGA(keto)AUUGC), respectively. The photoirradiation of r(CGCG(Br)UGCG)/r(C(m)GCAC(m)GCG) in Z-form RNA produced the 2'-keto guanosine ((keto)G) product r(CGC(keto)GUGCG), whereas almost no products were observed from the photoirradiation of r(CGCG(Br)UGCG)/r(C(m)GCAC(m)GCG) in A-form RNA. The present results indicate clearly that hydrogen (H) abstraction by the photochemically generated uracil-5-yl radical selectively occurs at the C2' position to provide a 2'-keto RNA product.
Assuntos
Bromouracila/química , RNA/química , Cromatografia Líquida de Alta Pressão , Luz , RNA/síntese química , RNA/metabolismo , Espectrometria de Massas por Ionização por ElectrosprayRESUMO
Ligands that stabilize the formation of telomeric DNA G-quadruplexes have potential as cancer treatments, because the G-quadruplex structure cannot be extended by telomerase, an enzyme over-expressed in many cancer cells. Understanding the kinetic, thermodynamic and mechanical properties of small-molecule binding to these structures is therefore important, but classical ensemble assays are unable to measure these simultaneously. Here, we have used a laser tweezers method to investigate such interactions. With a force jump approach, we observe that pyridostatin promotes the folding of telomeric G-quadruplexes. The increased mechanical stability of pyridostatin-bound G-quadruplex permits the determination of a dissociation constant K(d) of 490 ± 80 nM. The free-energy change of binding obtained from a Hess-like process provides an identical K(d) for pyridostatin and a K(d) of 42 ± 3 µM for a weaker ligand RR110. We anticipate that this single-molecule platform can provide detailed insights into the mechanical, kinetic and thermodynamic properties of liganded bio-macromolecules, which have biological relevance.
Assuntos
Aminoquinolinas/química , Quadruplex G , Ligantes , Ácidos Picolínicos/química , Aminoquinolinas/síntese química , DNA/metabolismo , Humanos , Cinética , Oxazóis/química , Ácidos Picolínicos/síntese química , Telomerase/antagonistas & inibidores , Telomerase/metabolismo , Telômero/química , TermodinâmicaRESUMO
Human telomere DNA is of intense interest because of its role in the biology of both cancer and aging. The single-stranded telomere terminus can adopt the structure of a G-quadruplex, which is of particular important for anticancer drug discovery many researchers have reported various G-quadruplex structures in the human telomere. Although the human telomere consists of a number of tandem repeats, higher-order G-quadruplex structures are less discussed due to the complexity of the structures. Here we examined the orientation of the ends of the G-quadruplex structures with consideration given to higher-order structures. We prepared end-extended and (Br)G-substituted oligonucleotides. Native PAGE analysis, CD measurements and NMR spectroscopy showed that the ends of stable G-quadruplex structures point in opposite directions. Our results indicate that the human telomere DNA is likely to form rod-like higher-order structures. This may provide important information for understanding telomere structure and the development of telomere G-quadruplex-binding molecules as telomerase inhibitors.
Assuntos
Quadruplex G , Oligonucleotídeos/química , Telômero/química , Sequência de Bases , Dicroísmo Circular , Eletroforese em Gel de Ágar , Humanos , Espectroscopia de Ressonância MagnéticaRESUMO
The human telomere terminus can adopt the structure of a G-quadruplex. This structure has become an attractive target for anticancer drugs, because it effectively inhibits telomerase activity. In this study, we investigated the orientation of both 5' and 3' ends of the stable G-quadruplex structure. To verify the orientation, we designed end-extended G-quadruplex forming oligonucleotides. We carried out gel electrophoresis and the NMR analysis and found that the ends of the stable G-quadruplex structure are located on opposite faces of each of the quadruplexes.
Assuntos
Quadruplex G , Oligonucleotídeos/química , Eletroforese em Gel de Poliacrilamida , Guanina/análogos & derivados , Guanina/química , Ressonância Magnética Nuclear BiomolecularRESUMO
The G-rich sequence in the human telomeric DNA can form the G-quadruplex structure. The G-quadruplex structure has become an attractive target for the anticancer drugs, because it effectively inhibits telomerase activity. Recently, the human telomere G-quadruplex in K(+) solution has been determined as a hybrid structure. This structure is called hybrid-1. More recently, the hybrid-2 G-quadruplex has been determined by NMR. Hybrid-2 G-quadruplex differs from hybrid-1 in its loop arrangement and strand orientation. Here, we propose the folding pathways of hybrid-1 and hybrid-2 G-quadruplex structures. In hybrid-1, we proposed two pathways. In one pathway, the random coil forms triplex-1; in another pathway, the random coil forms chair-1. Similarly, we proposed two pathways in hybrid-2. In one pathway, the random coil forms triplex-2; in another pathway, the random coil forms chair-2. The folding pathways of human telomeric hybrid-1 G-quadruplex and hybrid-2 G-quadruplex structures were proposed using MO calculation and molecular modelling.