1g3a
From Proteopedia
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STRUCTURE OF RNA DUPLEXES (CIGCGICG)2
Overview
Isoguanosine (iG) and isocytidine (iC) differ from guanosine (G) and, cytidine (C), respectively, in that the amino and carbonyl groups are, transposed. The thermodynamic properties of a set of iG, iC containing RNA, duplexes have been measured by UV optical melting. It is found that iG-iC, replacements usually stabilize duplexes, and the stabilization per iG-iC, pair is sequence-dependent. The sequence dependence can be fit to a, nearest-neighbor model in which the stabilities of iG--iC pairs depend on, the adjacent iG--iC or G--C pairs. For 5'-CG-3'/3'-GC-5' and, 5'-GG-3'/3'-CC-5' nearest neighbors, the free energy differences upon, iG-iC replacement are smaller than 0.2 kcal/mol at 37 degrees C, regardless of the number of replacements. For 5'-GC-3'/3'-CG-5', however, each iG--iC replacement adds 0.6 kcal/mol stabilizing free energy at 37, degrees C. Stacking propensities of iG and iC as unpaired nucleotides at, the end of a duplex are similar to those of G and C. An NMR structure is, reported for r(CiGCGiCG)(2) and found to belong to the A-form family. The, structure has substantial deviations from standard A-form but is similar, to published NMR and/or crystal structures for r(CGCGCG)(2) and, 2'-O-methyl (CGCGCG)(2). These results provide benchmarks for theoretical, calculations aimed at understanding the fundamental physical basis for the, thermodynamic stabilities of nucleic acid duplexes.
About this Structure
1G3A is a Protein complex structure of sequences from [1]. Full crystallographic information is available from OCA.
Reference
Stability and structure of RNA duplexes containing isoguanosine and isocytidine., Chen X, Kierzek R, Turner DH, J Am Chem Soc. 2001 Feb 21;123(7):1267-74. PMID:11456697
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