NMR study on the binding of d(GGAAATTTCC)2 with a positively charged pentacosapeptide

To obtain a better understanding of the electrostatic nature of protein-nucleic acid interactions, we have investigated the interaction of a double-stranded decamer d(GGAAATTTCC)2 with a synthetic arginine and lysine-rich pentacosapeptide (Pep25), using NMR and optical spectroscopy. The chemical shift data of the decamer under various experimental conditions show that the binding of Pep25 changes the conformation of the decamer in a different way, as compared to the conformational changes induced by a variation in temperature or ionic strength. The chemical shift results are interpreted in terms of ring current effects that emerge into a model for the conformational change, in which the double-stranded helix of the decamer undergoes a decrease of twist and rise to accommodate Pep25. The binding results indicate that the positively charged arginine and lysine side chains of Pep25 not only have a stabilising electrostatic interaction with the negatively charged backbone phosphates of d(GGAAATTTCC)2, but also that a stabilisation of the base pairs of d(GGAAATTTCC)2 by Pep25 takes place.