2axb

Crystal Structure Analysis Of A 2-O-[2-(methoxy)ethyl]-2-thiothymidine Modified Oligodeoxynucleotide Duplex

spinqualitylabelsall models 2axb, resolution 1.61Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Structural highlights 2axb is a 2 chain structure. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance. NonStd Res: S2M Resources: FirstGlance, OCA, RCSB, PDBsum Publication Abstract from PubMed Substitution of oxygen atoms by sulfur at various locations in the nucleic acid framework has led to analogs such as the DNA phosphorothioates and 4'-thio RNA. The phosphorothioates are excellent mimics of DNA, exhibit increased resistance to nuclease degradation compared with the natural counterpart, and have been widely used as first-generation antisense nucleic acid analogs for applications in vitro and in vivo. The 4'-thio RNA analog exhibits significantly enhanced RNA affinity compared with RNA, and shows potential for incorporation into siRNAs. 2-Thiouridine (s2U) and 5-methyl-2-thiouridine (m5s2U) are natural nucleotide analogs. s2U in tRNA confers greater specificity of codon-anticodon interactions by discriminating more strongly between A and G compared with U. 2-Thio modification preorganizes the ribose and 2'-deoxyribose sugars for a C3'-endo conformation, and stabilizes heteroduplexes composed of modified DNA and complementary RNA. Combination of the 2-thio and sugar 2'-O-modifications has been demonstrated to boost both thermodynamic stability and nuclease resistance. Using the 2'-O-[2-(methoxy)ethyl]-2-thiothymidine (m5s2Umoe) analog, we have investigated the consequences of the replacement of the 2-oxygen by sulfur for base-pair geometry and duplex conformation. The crystal structure of the A-form DNA duplex with sequence GCGTAT*ACGC (T* = m5s2Umoe) was determined at high resolution and compared with the structure of the corresponding duplex with T* = m5Umoe. Notable changes as a result of the incorporation of sulfur concern the base-pair parameter 'opening', an improvement of stacking in the vicinity of modified nucleotides as measured by base overlap, and a van der Waals interaction between sulfur atoms from adjacent m5s2Umoe residues in the minor groove. The structural data indicate only minor adjustments in the water structure as a result of the presence of sulfur. The observed small structural perturbations combined with the favorable consequences for pairing stability and nuclease resistance (when combined with 2'-O-modification) render 2-thiouracil-modified RNA a promising candidate for applications in RNAi. Stabilizing contributions of sulfur-modified nucleotides: crystal structure of a DNA duplex with 2'-O-[2-(methoxy)ethyl]-2-thiothymidines.,Diop-Frimpong B, Prakash TP, Rajeev KG, Manoharan M, Egli M Nucleic Acids Res. 2005 Sep 16;33(16):5297-307. Print 2005. PMID:16170156 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

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