Determination of Physical Properties of a Single Peptide by AFM Experiments

Dec. 23, 2009

By stretching a polymer in solution using single molecule techniques it is possible to infer about its physical properties. In particular, AFM stretching experiments allow for a full characterization of the elasto-mechanical properties of the sample under study, taking into account both statical and dynamical regimes [1]. In the presented work, single molecule AFM force spectroscopy experiments have been used to determine mechanical properties of a polymer obtained starting from the Exon 28 (Ex28) of the human elastin gene.

Elastin is a protein with important mechanical properties and, in particular, it shows quasi ideal elastic behavior associated to the presence of many hydrophobic unstructured domains (such as Ex28) into the protein structure. A typical result of an AFM length clamp stretching experiment is a force versus distance curve directly showing the response of the polymer to the external constant velocity stretching, from the tip-sample contact point up to the rupture of the bond between the probe and the sample (resulting in a steep peak). This experiment, performed in liquid environment, can give information on the mechanical properties of the molecule. The main contribution in the force exerted by the polymer on the AFM tip is due to the presence of a thermal bath driving the system towards a maximum entropy configuration. This entropic-only chain behaviour [2] can be described, switching to a mathematical description, in terms of the worm-like chain (WLC) model [3]. The Ex28 coded polymer has been used as a starting point to obtain bio-materials with specialized elasto-mechanical functions. In particular, a mutated polypeptide based on the EX28 sequence has been synthesisized (named EX28K) with the aim of obtaining a new polymer with the same mechanical and physical properties of the native molecule but with increased aggregation properties, induced by a cross-linking reaction. AFM stretching experiments have been used to verify the mechanical properties of the engineered proteins at a single molecule level. The obtained results allowed us not only to answer this question, but also to give some insight into the first aggregation steps of the polymer towards the formation of reticulated structures.

This poster was presented at NanoBioViews 2009; 14-15 October 2009: http://www.nanobioviews.net

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Massimo Vassalli
Institute of Biophysics
CNR
Via de Marini 6
16149 Genova, Italy
massimo.vassalli@cnr.it

Authors:
M. Vassalli
F. Sbrana
B. Tiribilli
B. Bochicchio
A. M. Tamburro

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Determination of Physical Properties of a Single Peptide by AFM Experiments

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