Substrate Properties and the Conformational State of Polyelectrolytes

National Institute Of Biomedical Imaging And Bioengineering, Bethesda

Investigators

Abstract

DNA and proteins belong to the class of polyelectrolytes, polymer molecules that, in solution, carry charge. We study primarily two very different such molecules, DNA and the glycoprotein aggrecan, a major structural component of articular cartilage. Their conformational states are strongly influenced by the ionic environment and multivalent ions affect intra- and intermolecular interactions and hence the conformational state of such molecules. In addition these molecules function in close proximity to organized, charged surfaces such as lipid bilayers and collagen matrices. We use a combination of techniques to study the conformational states and intermolecular interactions of the molecules adsorbed to positively and negatively charged surfaces. Atomic force microscopy (AFM) is used to visualize and analyze the conformations of the molecular assemblies at a single molecule level, while dynamic light scattering (DSL) and quartz crystal microbalance(QCM) are employed to estimate the changes in hydration and the size distribution in solution. During the past few months we studied the interactions of aggrecan with charged surfaces. We found that on positively charged surfaces the GAG chains of the aggrecan molecules were distinguishable, and their average dimensions were practically unaffected by the presence of salt ions. With increasing aggrecan concentration they formed clusters, and at higher concentrations they formed a continuous monolayer of conforming molecules. On negatively charged mica, the extent of aggrecan adsorption varied with salt composition.