1xam
From Proteopedia
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Cobalt hexammine induced tautameric shift in Z-DNA: structure of d(CGCGCA).d(TGCGCG) in two crystal forms.
Overview
We report here the crystal structure of the DNA hexamer duplex, d(CGCGCA)*d(TGCGCG) at 1.71 A resolution. The crystals, in orthorhombic, space group, were grown in the presence of cobalt hexammine, a known, inducer of the left-handed Z form of DNA. The interaction of this ion with, the DNA helix results in a change of the adenine base from the common, amino tautomeric form to the imino tautomer. Consequently the A:T base, pair is disrupted from the normal Watson-Crick base pairing to a 'wobble', like base pairing. This change is accommodated easily within the helix, and the helical parameters are those expected for Z-DNA. When the cobalt, hexammine concentration is decreased slightly in the crystallization, conditions, the duplex crystallizes in a different, hexagonal space group, with two hexamer duplexes in the asymmetric unit. One of these is situated, on a crystallographic 6-fold screw axis, leading to disorder. The, tautomeric shift is not observed in this space group. We show that the, change in inter-helix interactions that lead to the two different space, groups probably arise from the small decrease in ion concentration, and, consequently disordered positions for the ion.
About this Structure
1XAM is a Protein complex structure of sequences from [1] with NCO as ligand. Full crystallographic information is available from OCA.
Reference
Cobalt hexammine induced tautomeric shift in Z-DNA: the structure of d(CGCGCA)*d(TGCGCG) in two crystal forms., Thiyagarajan S, Rajan SS, Gautham N, Nucleic Acids Res. 2004 Nov 8;32(19):5945-53. Print 2004. PMID:15534365
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