Dynamic Interplay Between Macromolecular Conformation and Interfacial Behavior

The conformation of macromolecules such as nucleic acids, peptides, and proteins can have a dramatic effect on their affinity for an interface, as well as their mobility and reactivity. Most of the understanding of these interfacial phenomena is at the theoretical level along with some experimental observations from ensemble-averaged measurements. Single-molecule resonance energy transfer experiments, with the ability to resolve heterogeneous behavior lost by ensemble-averaged measurements, can provide direct experimental evidence of subtle conformational effects. This work uses total internal reflectance fluorescence microscopy (TIRFM) to measure the end-to-end distance of single-stranded DNA (ssDNA) and track its adsorption, desorption, and diffusion at the water interface with functionalized glass surfaces. Two states were observed in adsorbed ssDNA: an extended, weakly fluctuating conformation, and a more compact, highly fluctuating conformation. The extended conformation underwent fast diffusion and typically preceded desorption, indicating weaker surface attraction in this state. In addition to these results, single-molecule observations of helix-coil transitions in peptides on model hydrophobic surfaces will be presented.