Polypeptide-Solvent Interactions Measured by Single Molecule Force Spectroscopy
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0898-L06-06-NN04-06.1
Polypeptide-Solvent Interactions Measured by Single Molecule Force Spectroscopy Alexei Valiaev1,3, Dong Woo Lim2,3, Ashutosh Chilkoti2,3,Scott Schmidler4, Stefan Zauscher1,3 1
Duke University, Department of Mechanical Engineering and Materials Science Duke University, Department of Biomedical Engineering 3 Center for Biologically Inspired Materials and Materials Systems 4 Institute of Statistics and Decision Sciences 2
ABSTRACT Stimulus-responsive biomolecules have attracted a large research interest because of their potential application in various areas such as drug delivery, actuators and sensing devices at the nanoscale. Using single-molecule force spectroscopy (SMFS) we studied elastin-like polypeptides (ELPs). These stimulus-responsive polypeptides undergo an inverse temperature transition, accompanied by a large conformational change, when the solvent quality is changed by increasing the temperature or by addition of salt. Understanding the relationship between peptide sequence and mechanisms of force generation can provide a route to engineer ELPs with desirable mechano-chemical properties. Here we studied the effect of solvent quality and type of guest residue on the mechanical properties of ELPs on the single-molecule level. We used a novel statistical approach to estimate polymer elasticity parameters from model fits to the data. With this approach we were able to resolve small changes in the Kuhn segment length distributions associated with different molecular architectures. We then show that these mechanical differences likely arise from differences in the hydrophobic hydration of sidegoups, in line with recent predictions from molecular dynamics simulations. INTRODUCTION Over the last decade, AFM force spectroscopy has been increasingly used to study various biological[1] and synthetic macromolecules[2] in aqueous environments. We are using force spectroscopy to study the conformational mechanics of elastin-like polypeptides (ELPs). ELPs are stimulus-responsive polypeptides (SRPs), which undergo an inverse phase transition when exposed to an environmental stimulus such as an increase in temperature or change in ionic strength[3]. The mechanical properties of ELPs are of particular interest because ELPs can be exploited for force generation,[3] and provide the building blocks for engineered protein elastomers. The motivation for our work is to understand the conformational mechanics and “stiffness” of ELPs on the molecular scale, and thus to provide a guide to rational genetic engineering of stimulus-responsive biomolecules with specific mechanical properties. Study of ELPs may also give insight into the ongoing debate over mechanisms of elasticity in native elastin[3, 4]. Many polymers and polypeptides, including ELPs, are intrinsically random and have properties that are independent of the details of the local chemical architecture. The forceextension behavior of such polymers can be described by polymer elasticity models such as the freely jointed chain (FJC), [1] or the worm
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