Book of Abstracts: Albany 2003
June 17-21 2003
Adaptability and Dynamics in RNA Ligand Interactions: The Malachite Green Binding Aptamer
RNA plays a central role in many biological processes and is therefore an important target for drug development. In recent years an increasing wealth of structural and functional information about RNA ? ligand complexes has been obtained using in vitro selected RNAs (aptamers). However, all those studies focused on structure and changes of the nucleic acid and mostly considered the ligand as a rigid target. In order to develop a detailed picture of ligand structure and dynamics in RNA ? small molecule complexes the Malachite Green binding aptamer was studied. Isotopically labeled ligand in complex with RNA was analyzed by NMR spectroscopy in solution. The surprisingly asymmetric changes in the 13C chemical shift of the ligand methyl groups indicate that the dye undergoes changes in its conformation and charge distribution upon binding (1). The role of the RNA electrostatic field in this interaction was explored using ab initio calculations of the ligand structure and charge distribution. The results indicate that the uneven charge distribution in the RNA binding pocket provides a major contribution to the driving force of the ligand structural changes. The observation that not only the RNA adapts to the ligand in what is called adaptive binding, but the ligand itself also undergoes conformational changes (?induced fit?), is crucial for the rational design of RNA ligands and for understanding the properties of RNA ? ligand complexes.
In order to further explore the role of electrostatics in RNA ? ligand interactions we have synthesized a variety of Malachite Green derivatives with altered electronic structure. Here we present the analysis of binding affinity and kinetics for these derivatives using both experimental and computer simulation approaches.
References and Footnotes
University of California at Davis