NMR-STUDY ON THE BINDING OF D(GGAAATTTCC)(2) WITH A POSITIVELY CHARGED PENTACOSAPEPTIDE

To obtain a better understanding of the electrostatic nature of protei n-nucleic acid interactions, we have investigated the interaction of a double-stranded decamer d(GGAAATTTCC)(2) with a synthetic arginine an d lysine-rich pentacosapeptide (Pep25), using NMR and optical spectros copy. The chemical shift data of the decamer under various experimenta l conditions show that the binding of Pep25 changes the conformation o f the decamer in a different way, as compared to the conformational ch anges induced by a variation in temperature or ionic strength. The che mical shift results are interpreted in terms of ring current effects t hat emerge into a model for the conformational change, in which the do uble-stranded helix of the decamer undergoes a decrease of twist and r ise to accommodate Pep25. The binding results indicate that the positi vely charged arginine and lysine side chains of Pep25 not only have a stabilising electrostatic interaction with the negatively charged back bone phosphates of d(GGAAATTTCC)(2), but also that a stabilisation of the base pairs of d(GGAAATTTCC)(2) by Pep25 takes place. (C) 1998 Else vier Science B.V. All rights reserved.