1d45
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(New page: 200px<br /><applet load="1d45" size="450" color="white" frame="true" align="right" spinBox="true" caption="1d45, resolution 1.900Å" /> '''DNA DODECAMER C-G-C...)
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Revision as of 00:19, 25 November 2007
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DNA DODECAMER C-G-C-G-A-A-T-T-C-G-C-G/HOECHST 33258 COMPLEX:-25 DEGREES C, PIPERAZINE DOWN
Overview
The crystal structure of the complex of Hoechst 33258 and the DNA, dodecamer C-G-C-G-A-A-T-T-C-G-C-G has been solved from X-ray data, collected at three different low temperatures (0, -25, and -100 degrees, C). Such temperatures have permitted collection of higher resolution data, (2.0, 1.9, and 2.0 A, respectively) than with previous X-ray studies of, the same complex. In all three cases, the drug is located in the narrow, central A-A-T-T region of the minor groove. Data analyses at -25 and -100, degrees C (each with a 1:1 drug/DNA ratio in the crystallizing solution), suggest a unique orientation for the drug. In contrast, two orientations, of the drug were found equally possible at 0 degrees C with a 2:1 drug/DNA, ratio in solution. Dihedral angles between the rings of Hoechst 33258, appear to change in a temperature-dependent manner. The drug/DNA complex, is stabilized by single or bifurcated hydrogen bonds between the two N-H, hydrogen-bond donors in the benzimidazole rings of Hoechst and adenine N3, and thymine O2 acceptors in the minor groove. A general preference for AT, regions is conferred by electrostatic potential and by narrowing of the, walls of the groove. Local point-by-point AT specificity follows from, close van der Waals contacts between ring hydrogen atoms in Hoechst 33258, and the C2 hydrogens of adenines. Replacement of one benzimidazole ring by, purine in a longer chain analogue of Hoechst 33258 could make that, particular site GC tolerant in the manner observed at imidazole, substitution for pyrrole in lexitropsins.
About this Structure
1D45 is a Protein complex structure of sequences from [1] with HT and MG as ligands. Full crystallographic information is available from OCA.
Reference
Low-temperature crystallographic analyses of the binding of Hoechst 33258 to the double-helical DNA dodecamer C-G-C-G-A-A-T-T-C-G-C-G., Quintana JR, Lipanov AA, Dickerson RE, Biochemistry. 1991 Oct 22;30(42):10294-306. PMID:1718416
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