Induction of self-structure in polyriboadenylic acid by the benzophenanthridine plant alkaloid chelerythrine: a spectroscopic approach

Abstract

The naturally occurring benzophenanthridine plant alkaloid chelerythrine (CHL) was found to bind strongly to single-stranded polyriboadenylic acid (poly-A) with a high association constant of the order of 10⁷ M⁻¹. The association was monitored by various spectroscopic and viscometric techniques. Binding of the alkaloid induced self-structure formation of a poly-A helix that showed cooperative melting transition in circular dichroism. The mode of binding of CHL to poly-A was intercalation, as revealed by fluorescence quenching, sensitization of fluorescence experiment and viscosity measurement. Transfer of fluorescence energy from RNA bases to CHL has been demonstrated from fluorimetric studies. Thermodynamic data obtained from temperature dependence of the binding constant revealed that association was driven by a negative enthalpy change and opposed by a negative entropy change. Since the interaction of naturally occurring small molecules with RNA is an active area of research, this study renders the scope of exploring chelerythrine as RNA targeted therapeutic agent.