Single Molecule Study of Cis-Platin DNA Interaction

Abstract

Background: Cis-platin belongs to the family of inorganic metal drugs which has a success rate of ∼ 90 % against testicular and ovarian cancer. Substantial research has been done on cisplatin-DNA interaction using various techniques including atomic force microscopy AFM, however, the exact mechanical change (e.g. bend angle and ridigidty) in DNA due to its interaction with a single molecule of cis-platin is controversial. Elucidation of these parameters will enhance our understanding of how proteins interact with cis-platin and will, thus, enhance our understanding of the successes and limitations of cis-platin.Objectives & Methods: Using statistical analysis of AFM imaging and simulations based on the worm-like-chain model we investigated the interaction of cis-platin with DNA at the single molecule level to determined the cis-platin induced DNA bend angle and change in DNA mechanical properties. We used three constructs of DNA (300 bp) with a single GG, a single AG or two, in-phase GG sites in the center. We measured the contour length (L), end to end distance(R) of DNA and DNA-cisplatin complexes, and determined the persistence length (P), bend angle β, and local flexibility around the cis-platin site.Results: R/L Distribution of the DNA-cisplatin complex showed a small but significant change when compared with the normal DNA distribution; the cisplatin-induced bend angle β was measured to be ∼38°. R/L distribution of the simulated DNA molecules matched the experimental data.Conclusions: The R/L distribution of the DNA-cisplatin complex vs normal, of AFM images and simulated DNA molecules shows that the DNA is damaged locally at the platination site while retaining its global mechanical properties. Our bend angle agrees with the X-ray and the gel-electrophoresis data further confirming the specificity of our technique in capturing the DNA-cisplatin interaction.