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Introduction

The intercalation of DNA and drug compounds has been studied thoroughly; in this case the nucleotide d(CGTACG) was complexed with an anthraquinone derivative. This derivative, 1,5-bis[3-(diethylamino)propionamido]anthracene-9,10-dione, provided researchers with the information needed to solve using X-Ray crystallography. Along with the structure, the important forces involved in binding were analyzed and described as heavily reliant on cations. Furthermore, the binding site seems to be specific to anthracene and similar molecules. Therefore, the potential for drug compounds to be carried by this nucleotide complex requires further research.

Overall Structure

The 1xcs (model at right) complex is a small, simple globular DNA-drug complex, and as such lacks any traditional protein structures such as secondary beta sheets or alpha helices. The complex consists of two complimentary strands of DNA. A simplified model of 1xcs is shown with the nitrogenous bases removed for clarity. The deoxyribose backbones can be followed from 5' to 3' following along each strand from blue to red. Note that the strands are antiparallel where they are (hydrogen) bonded. visualizes this bonding in the middle region of the complex, again following each strand from blue to red from 5' to 3' ends.

The 1xcs complex also binds to metal ions in more than one location, which have been shown to be important to the drug's binding ability. Different metal ions may be present, including Na(+) and Co(2+). These metal ions sites are colored pink in scene. One other metal binding site was noted, which had the ability to bind . This barium binding site is believed to strengthen the ability of the O6 site to bind cobalt. This ability to strongly bind metal ions was also important for x-ray crystallographic purposes, as it enabled researchers to form crystals of the complex by relying on interactions between neighboring molecules' binding sites.

Binding Interactions

Additional Features

In , one can see that the anthraquinone derivative is located between the two carbon backbones and the base pairs of DNA. This interrupts the function of taq polymerase and telomerase. Taq polymerase is in part responsible for the replication of DNA and consequently, cell replication. Telomeres are repeating sections of non-coding DNA that protect the ends of coding sections of DNA from degradation. Each time a cell divides, telomeres shorten. Over time, telomeres shorten, to the point of disappearance, causing DNA degradation and cell death. Telomerase builds up these protective sections of DNA. Cancer is characterized as an uncontrolled rate of cell growth. By inhibiting the replication DNA and the construction of protective telomeres, this drug serves to slow and stop cancerous cell growth.

Quiz Question 1

Why is it important for the protein to bind ? A unique site is the __ ion found associated with the , which gives additional strength to the guanine–Co2+–guanine interaction. A Mg2+ B Co2+ C Ba2+ D Mg2+

See Also

• 1bp8
• 1d3x
• 1p3x

Credits

Introduction - Daniel Marco

Overall Structure - Nathaneal Park

Drug Binding Site - Annie Burton

Additional Features - Michael Beauregard

Quiz Question 1 - Jianlong Li

References

1. ↑ Valls N, Steiner RA, Wright G, Murshudov GN, Subirana JA. Variable role of ions in two drug intercalation complexes of DNA. J Biol Inorg Chem. 2005 Aug;10(5):476-82. Epub 2005 Sep 23. PMID:15926069 doi:10.1007/s00775-005-0655-3