Reconstructing the free-energy landscape of a polyprotein by single-molecule experimentsA. 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
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.
82.37.Rs - Single molecule manipulation of proteins and other biological molecules.
87.15.La - Mechanical properties.
05.70.Ln - Nonequilibrium and irreversible thermodynamics.
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