Beads-on-String Structure of the Electrostatic Complex of DNA with a High-Generation PAMAM Dendrimer

The electrostatic complexes of polyanionic DNA with cationic dendrimer have been considered as a potential non-viral vector for gene delivery and a model system for understanding DNA-histone interaction. Although it is believed that the gene transfection efficiency may be influenced by the structure of the complex, the supramolecular structure of DNA-dendirmer complexes and its dependence on various system parameters such as dendrimer generation number, charge density, charge ratio and ionic strength are not well resolved. In this study, we investigate the structure of the complex of DNA with polyamidoamine (PAMAM) dendrimer of generation nine (G9) by means of synchrotron small angle X-ray scattering (SAXS). It is found that DNA is always able to wrap around the dendrimer to yield the beads-on-string structure irrespective of the charge density of the dendrimer. The effect of charge density on the persistence length of the chromatin-like fiber thus formed and the pitch length of the DNA superheix wrapping around the dendrimer are elucidated from the calculation of the SAXS profiles based on beads-on-string structure models. The first section in your paper