AVS 53rd International Symposium
    Biomaterial Interfaces Friday Sessions
       Session BI-FrM

Paper BI-FrM12
Single-Molecule Force Spectroscopy of Stimulus-Responsive Polypeptides

Friday, November 17, 2006, 11:40 am, Room 2014

Session: Biomolecular Surface Characterization II
Presenter: S. Zauscher, Duke University
Authors: S. Zauscher, Duke University
A. Valiaev, Duke University
A. Chilkoti, Duke University
T. Oas, Duke University
Correspondent: Click to Email
Stimulus-responsive elastin-like polypeptides (ELPs) experience a large entropic collapse when exposed to an environmental stimulus, such as an increase in temperature. While interfacial applications of ELPs have been prototypically demonstrated, a systematic investigation of the phase transition behavior at the solid-liquid interface and on the single-molecule level is lacking. We will present results from single molecule force-spectroscopy (SMFS) measurements probing the force-extension and conformational behavior of ELPs, below and above their transition temperature. We show that ELPs are well described by a random coil polymer model, suggesting the absence of significant secondary structure. Furthermore, we show that single molecule force spectroscopy is able to differentiate different ELP constructs by distinguishing differences in the hydrophobic hydration of side chains. This suggests that SMFS has potential diagnostic abilities for studying the hydration behavior of proteins. We also noticed that some ELP force-extension curves showed temperature independent deviations that could not be described by polymer elasticity models developed for random polymers. We argue that the observed deviations arise from the force-induced cis-trans isomerization of prolines, which are repeated every fifth residue in the main chain of ELPs. We present evidence for this mechanism by Monte Carlo simulations of the force-extension curves using an elastically coupled two-level system. Furthermore, we show results from control experiments with poly-L-proline that demonstrate the similarity of the conformational transition between poly-L-proline and ELPs. We believe that our work is the first demonstration of force induced cis-trans isomerization in proline containing polypeptides. Our results suggest that SMFS could be used to assay proline cis-trans isomerization in proteins and may thus have significant potential diagnostic utility.