Issue
EPL
Volume 82, Number 5, June 2008
Article Number 58006
Number of page(s) 5
Section Interdisciplinary Physics and Related Areas of Science and Technology
DOI http://dx.doi.org/10.1209/0295-5075/82/58006
Published online 29 May 2008
EPL, 82 (2008) 58006
DOI: 10.1209/0295-5075/82/58006

Reconstructing the free-energy landscape of a polyprotein by single-molecule experiments

A. Imparato1, 2, F. Sbrana3 and M. Vassalli3, 4

1  Dipartimento di Fisica and CNISM, Politecnico di Torino - c. Duca degli Abruzzi 24, Torino, Italy, EU
2  INFN, Sezione di Torino - Torino, Italy, EU
3  CSDC-Dipartimento di Fisica, Università di Firenze - via Sansone, 1, Sesto Fiorentino, Italy, EU
4  Istituto Sistemi Complessi, CNR - via Madonna del Piano 10, Sesto Fiorentino, Italy, EU


received 21 December 2007; accepted in final form 17 April 2008; published June 2008
published online 29 May 2008

Abstract
The mechanical unfolding of an engineered protein composed of eight domains of Ig27 is investigated by using atomic force microscopy. Exploiting a fluctuation relation, the equilibrium free energy as a function of the molecule elongation is estimated from pulling experiments. Such a free energy exhibits a regular shape that sets a typical unfolding length at zero force of the order of 20 nm. This length scale turns out to be much larger than the kinetic-unfolding length that is also estimated by analyzing the typical rupture force of the molecule under dynamic loading.

PACS
82.37.Rs - Single molecule manipulation of proteins and other biological molecules.
87.15.La - Mechanical properties.
05.70.Ln - Nonequilibrium and irreversible thermodynamics.

© EPLA 2008