This old version of Proteopedia is provided for student assignments while the new version is undergoing repairs. Content and edits done in this old version of Proteopedia after March 1, 2026 will eventually be lost when it is retired in about June of 2026.
Apply for new accounts at the new Proteopedia. Your logins will work in both the old and new versions.
1d81
From Proteopedia
|
THE CONFORMATIONAL VARIABILITY OF AN ADENOSINE. INOSINE BASE-PAIR IN A SYNTHETIC DNA DODECAMER
Overview
A crystal structure analysis of the synthetic deoxydodecamer d(CGCAAATTIGCG) which contains two adenosine.inosine (A.I) mispairs has revealed that, in this sequence, the A.I base-pairs adopt a A(anti).I(syn) configuration. The refinement converged at R = 0.158 for 2004 reflections with F greater than or equal to 2 sigma(F) in the range 7.0-2.5A for a model consisting of the DNA duplex and 71 water molecules. A notable feature of the structure is the presence of an almost complete spine of hydration spanning the minor groove of the whole of the (AAATTI)2 core region of the duplex. pH-dependent ultraviolet melting studies have suggested that the base-pair observed in the crystal structure is, in fact, a protonated AH+ (anti).I(syn) species and that the A.I base-pairs in the sequence studied display the same conformational variability as A.G mispairs in the sequence d(CGCAAATTGGCG). The AH+(anti).I(syn) base-pair predominates below pH 6.5 and an A(anti).I(anti) mispair is the major species present between pH 6.5 and 8.0. The protonated base-pairs are held together by two hydrogen bonds one between N6(A) and O6(I) and the other between N1(A) and N7(I). This second hydrogen bond is a direct result of the protonation of the N1 of adenosine. The ultraviolet melting studies indicate that the A(anti).I(anti) base-pair is more stable than the A(anti).G(anti) base-pair but that the AH+(anti).I(syn) base pair is less stable than its AH+(anti).G(syn) analogue. Possible reasons for this observation are discussed.
About this Structure
1D81 is a Protein complex structure of sequences from [1]. Full crystallographic information is available from OCA.
Reference
The conformational variability of an adenosine.inosine base-pair in a synthetic DNA dodecamer., Leonard GA, Booth ED, Hunter WN, Brown T, Nucleic Acids Res. 1992 Sep 25;20(18):4753-9. PMID:1408788
Page seeded by OCA on Thu Feb 21 12:13:59 2008
