Investigation of the formation of binary or ternary comlexes of quadruplex-forming DNA sequences of the insulin-linked polymorphic region (ILPR) with organic ligands and insulin

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Studies of the interactions between nucleic acids, proteins and small ligands contribute significantly to the fundamental understanding of biochemical processess and hence - in the long term - to the development of strategies for the therapy of acute or chronic diseases. In particular, the structures and functions of quadruplex DNA attract increasing attention. Quadruplex structures are formed in guanine-rich DNA sequences through the assembly and stacking of guanine quartets, and they are proposed to be relevant intermediates in physiological processes and promising targets for selective drugs. In this context the insulin-linked polymorphic region (ILPR) represents a remarkable G-rich sequence that is located in the promoter region of the human insulin gene und whose physiological function is explained in part by its proponsity to form quadruplex structures. It is established that the association of ligands may affect the structures and biological activity of quadruplex-containing DNA sequences; however, this aspect has been neglected so far in studies of ILPR-DNA. Therefore this research project aims at the first systematic investigation of the interactions of known and newly developed ligands with quadruplex-forming ILPR sequences. With this approach selective ILPR-DNA ligands shall be identified and those factors will be assessed that govern the ligand-induced stabilization of quadruplex structures in ILPR-DNA and the resulting structural changes. Another goal of the project is the examination of the association of insulin with ILPR-DNA, because all literature data point to a biological function of this interaction. In particular, it will be examined whether a ligand increases the strength of the insulin-DNA interaction by the formation of a ternary complex or whether it inhibits the complex formation, as both events may have an effect on the biological activity. In addition, derivatives shall be identified amongst the investigated ligands that may be used as fluorescent probes for efficient detection of quadruplex structures in ILPR-DNA by emission light-up effects.