MSE Seminar Series: Joonil Seog
Friday, September 27, 2013
1:00 p.m.-2:00 p.m.
Room 2110, Chemical and Nuclear Engineering Bldg
Dynamic Self-Assembly of Biomacromolecules at the Single Molecule and Nanoscale Level
Department of Materials Science and Engineering
University of Maryland
One-dimensional nanostructures are ideal building blocks for functional nanoscale assembly. Peptide based nanofibers have a high potential in building smart hierarchical structures due to their tunable structures at the single residue level and their ability to reconfigure themselves in response to environmental stimuli. As an external stimulus, we applied mechanical force using atomic force microscopy (AFM). Under nanomechanical force silk-elastin-like peptide polymer (SELP) self-assembles into amyloid nanofibers through dynamic conformational changes on a mica substrate. Time lapse lateral force microscopy revealed that mechanical stretching of a single or multiple SELP molecules is a key molecular event for amyloid nucleation. The mechanically induced nucleation allows for positional and directional control of amyloid assembly in vitro, which we demonstrate by creating single nanofibers at predetermined sites. At the single molecule level, DNA condensation by cationic peptides was investigated using optical tweezers. Force-extension curves showed characteristic force plateaus and hysteresis between stretching and relaxation cycles. Upon environmental changes such as concentrations, pH and divalent cations, force profiles changed significantly indicating that mechanical properties of DNA:cationic peptide complex are dynamically regulated. Implications from our single molecule studies for designing efficient carriers for gene therapy will be discussed.